Antimicrobials — MCQs

Q: A patient from a North-Eastern state was diagnosed to have an infection with P. Falciparum malaria. What is the most appropriate treatment for this patient?

Artemether plus lumefantrine. ***Artemether plus lumefantrine*** - Artemether-lumefantrine is the recommended first-line treatment for **uncomplicated P. falciparum malaria** in regions with known **chloroquine resistance**, such as North-Eastern India. - This combination therapy, an **Artemisinin-based Combination Therapy (ACT)**, is highly effective due to its rapid parasiticidal action and synergy. *Chloroquine* - Chloroquine resistance in **P. falciparum malaria** is widespread, particularly in many parts of India, including the North East. - Using chloroquine alone would likely lead to **treatment failure** and worsening of the patient's condition. *Mefloquine* - Mefloquine is an alternative treatment option, but it has significant drawbacks including **neuropsychiatric side effects** (e.g., anxiety, depression, hallucinations) and a long half-life. - It is often reserved for specific situations or as a second-line agent when ACTs are not available or contraindicated. *Sulfadoxine plus pyrimethamine* - **Sulfadoxine-pyrimethamine (SP)** is an older antimalarial drug combination that is not recommended as first-line treatment for **uncomplicated P. falciparum malaria** due to widespread **parasite resistance**. - While it was formerly used for prophylaxis and intermittent presumptive treatment, its efficacy against P. falciparum has significantly declined. *Quinine plus doxycycline* - **Quinine plus doxycycline** is an effective alternative for treating **P. falciparum malaria**, particularly in **severe cases** or when ACTs are contraindicated or unavailable. - However, it is **not the first-line treatment** for uncomplicated malaria due to longer treatment duration (7 days), more frequent dosing, and potential side effects (cinchonism, GI disturbances). - Requires adherence to a multi-day regimen, making ACTs more practical for uncomplicated cases.

Q: Which of the following chelating agents is indicated in iron overdose?

Desferrioxamine. ***Desferrioxamine*** - **Desferrioxamine** is a **chelate** formed by the bacterium *Streptomyces pilosus* that has a high affinity for **iron**. - It is currently the most commonly used chelating agent for **acute iron overdose** and **chronic iron overload** conditions like hemochromatosis or transfusional hemosiderosis. *BAL* - **BAL (dimercaprol)** is a chelating agent primarily used for poisoning with **arsenic**, **mercury**, and **gold**. - It works by forming stable cyclic compounds with these metals, facilitating their excretion. *Calcium Edetate* - **Calcium edetate (Calcium-EDTA)** is primarily used for **lead poisoning**. - It works by forming a stable, water-soluble complex with lead, which is then excreted by the kidneys. *DTPA* - **Diethylenetriamine pentaacetate (DTPA)** is a chelating agent primarily used for poisoning with **plutonium** and other **radioactive metals**. - It is not indicated for iron overdose. *Penicillamine* - **Penicillamine** is a chelating agent primarily used for **copper** overload (Wilson's disease) and can also be used for **lead** and **mercury** poisoning. - It is not effective for iron chelation in overdose situations.

Q: In which phase of clinical trials is drug dosing typically determined?

Phase 1. ***Phase 1*** - This phase involves a small group of **healthy volunteers** to assess the drug's safety, **pharmacokinetics (PK)**, and establish an initial dosing range. - The primary goal is to determine a **safe dosage level**, establish the **maximum tolerated dose (MTD)**, and identify potential side effects. - This is where drug dosing is **typically determined**. *Phase 0* - This is an exploratory phase involving **microdosing** studies with subtherapeutic doses. - The goal is to gather preliminary PK/PD data, but **not to determine therapeutic dosing**. *Phase 2* - This phase involves a larger group of **patients** with the condition to be treated. - The main goal is to evaluate the drug's **effectiveness** and further assess safety, but not primarily to determine initial dosing. *Phase 3* - This phase involves a large number of patients across multiple sites to confirm the drug's **efficacy** and monitor side effects in a broader population. - Dosing strategies have generally been established in earlier phases, and this phase primarily validates them. *Phase 4* - This phase occurs **after a drug has been approved** and marketed. - It involves ongoing surveillance to monitor long-term effects, collect additional information on safety, and identify new uses, but not initial dose determination.

Q: Which of the following drugs, when given with erythromycin, can cause QT prolongation and Torsades de Pointes?

Astemizole. ***Astemizole*** - **Astemizole** is a second-generation antihistamine that undergoes extensive metabolism by the **CYP3A4 enzyme**. - Concomitant use with **erythromycin**, a potent **CYP3A4 inhibitor**, significantly increases astemizole plasma concentrations, leading to **QT prolongation** and an elevated risk of **Torsades de Pointes**. *Cetirizine* - **Cetirizine** is another second-generation antihistamine that is primarily eliminated via **renal excretion** and does not undergo significant CYP450 metabolism. - Therefore, its co-administration with **erythromycin** does not typically lead to clinically significant drug interactions impacting cardiac repolarization. *Fexofenadine* - **Fexofenadine** is a second-generation antihistamine and active metabolite of terfenadine that is primarily eliminated via **biliary excretion** and has minimal hepatic metabolism. - While it is a substrate of **P-glycoprotein** (which can be inhibited by erythromycin), fexofenadine has a much safer cardiac profile and does not typically cause **QT prolongation** even with CYP3A4 inhibitors. *Loratadine* - **Loratadine** is a second-generation antihistamine that is metabolized by **CYP2D6** and **CYP3A4**, but its active metabolite, desloratadine, has a lower propensity for QT prolongation. - While erythromycin is a CYP3A4 inhibitor, the risk of **QT prolongation** with **loratadine** is generally considered much lower than with astemizole, even with concurrent use. *Promethazine* - **Promethazine** is a first-generation antihistamine and phenothiazine derivative that primarily acts as a **dopamine D2 receptor antagonist**. - While it can cause **QT prolongation** on its own at high doses, its metabolism is complex and not predominantly dependent on **CYP3A4** to the extent that interaction with **erythromycin** poses the same severe risk as with astemizole.

Q: Aprepitant is a drug used in the treatment of some cases of chemotherapy-induced nausea and vomiting. What is the mechanism of action of this drug?

NK1 antagonist. ***NK1 antagonist*** - **Aprepitant** is a selective, high-affinity antagonist of the **neurokinin 1 (NK1) receptor**, which is activated by **substance P**. - By blocking NK1 receptors in the brainstem's **vomiting center**, aprepitant prevents nausea and vomiting, especially in chemotherapy-induced cases. - Aprepitant is particularly effective for **acute and delayed** chemotherapy-induced nausea and vomiting (CINV). *NK3 antagonist* - While **neurokinin 3 (NK3) receptors** are present in the central nervous system, their specific role in chemotherapy-induced nausea and vomiting is less prominent. - Aprepitant does not primarily target NK3 receptors; its antiemetic action is mediated through NK1 blockade. *NK1 agonist* - An **NK1 agonist** would activate the NK1 receptor, potentially *inducing* nausea and vomiting, which is the opposite of the desired therapeutic effect of aprepitant. - Agonists are typically used to stimulate a receptor, not block it as is done with aprepitant. *NK2 antagonist* - **Neurokinin 2 (NK2) receptors** are also part of the tachykinin receptor family, but they are not the primary target for antiemetic drugs like aprepitant. - While NK2 receptors play roles in smooth muscle contraction and inflammation, blocking them is not the mechanism by which aprepitant prevents nausea and vomiting. - Aprepitant's antiemetic efficacy is specifically due to **NK1 receptor antagonism**. *NK2 agonist* - **Neurokinin 2 (NK2) receptors** are also part of the tachykinin receptor family, but they are not the primary target for antiemetic drugs like aprepitant. - Activating NK2 receptors would not provide the antiemetic effect seen with aprepitant, as NK1 receptor antagonism is crucial.

Q: Methotrexate use causes reduced synthesis of which of the following?

TMP. ***TMP (Thymidylate)*** - Methotrexate is a **folate analog** that inhibits **dihydrofolate reductase (DHFR)**, preventing the regeneration of tetrahydrofolate (THF) from dihydrofolate. - **Tetrahydrofolate** is essential for **thymidylate synthase**, which converts dUMP to **TMP (thymidylate)** - this is the **most directly and significantly affected** nucleotide synthesis pathway. - Reduced TMP synthesis leads to impaired DNA synthesis and is the **primary mechanism** of methotrexate's cytotoxic effects. *CMP (Cytidine monophosphate)* - CMP synthesis occurs via the **de novo pyrimidine pathway** starting from carbamoyl phosphate and aspartate, forming UMP, which is then converted to CMP. - This pathway **does not require tetrahydrofolate** cofactors, so methotrexate does not significantly affect CMP synthesis directly. *GMP (Guanosine monophosphate)* - GMP is a purine nucleotide whose synthesis **does require tetrahydrofolate** derivatives (N10-formyl-THF) at two steps in the de novo purine pathway. - However, the effect on GMP is **less direct and less pronounced** than on TMP synthesis, and cells can partially compensate through salvage pathways. *AMP (Adenosine monophosphate)* - AMP is also a purine nucleotide that requires **N10-formyl-THF** cofactors during de novo synthesis (same pathway branch point as GMP). - Like GMP, it is affected but **less directly than TMP**, and salvage pathways provide alternative synthesis routes. *UMP (Uridine monophosphate)* - UMP is synthesized through the **de novo pyrimidine pathway** which does not require folate cofactors. - Methotrexate does not inhibit the enzymes (carbamoyl phosphate synthetase II, aspartate transcarbamoylase, dihydroorotase, etc.) involved in UMP synthesis.

Antimicrobials US Medical PG Practice Questions and MCQs

Question 1: A tourist with a travel history to India presents with complaints of abdominal pain and multiple episodes of watery diarrhea. He reports having food at a local restaurant the previous night. Which of the following antidiarrheal agents is used in this condition?

A. Bismuth subsalicylate
B. Octreotide
C. Loperamide
D. Rifaximin (Correct Answer)
E. Ciprofloxacin

Explanation: ***Rifaximin*** - This patient's symptoms, including **abdominal pain**, **watery diarrhea**, and a recent **travel history to India** coupled with eating at a local restaurant, strongly suggest **traveler's diarrhea**, often caused by bacterial pathogens. - **Rifaximin** is a non-absorbable antibiotic specifically approved for treating non-invasive traveler's diarrhea, as it targets causative bacteria in the gut lumen with minimal systemic absorption. - Rifaximin is preferred due to its **excellent safety profile**, minimal systemic effects, and targeted action against enteric pathogens. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic that can be effective for traveler's diarrhea and has been used historically for this indication. - However, rifaximin is now preferred over ciprofloxacin due to increasing **fluoroquinolone resistance** among enteric pathogens, systemic absorption leading to more side effects, and FDA warnings about serious adverse effects associated with fluoroquinolones. - Ciprofloxacin may be reserved for more severe or invasive diarrhea cases. *Bismuth subsalicylate* - While **bismuth subsalicylate** can be used for symptomatic relief in traveler's diarrhea due to its anti-secretory and anti-inflammatory properties, it is not an antimicrobial agent. - It works by reducing fluid secretion and inflammation but does not directly address the underlying bacterial infection to the same extent as rifaximin. *Octreotide* - **Octreotide** is a somatostatin analog primarily used to treat severe, refractory diarrhea associated with conditions like neuroendocrine tumors or chemotherapy, not typical bacterial traveler's diarrhea. - Its mechanism involves inhibiting gastrointestinal hormone secretion and reducing intestinal motility, which is too potent for this common, self-limiting condition. *Loperamide* - **Loperamide** is an opioid-receptor agonist that acts as an anti-motility agent, reducing the frequency of bowel movements. - It is generally contraindicated as a primary treatment for traveler's diarrhea when an invasive bacterial infection is suspected, as it can prolong the retention of toxins and pathogens in the gut.

Question 2: A patient from a North-Eastern state was diagnosed to have an infection with P. Falciparum malaria. What is the most appropriate treatment for this patient?

A. Chloroquine
B. Mefloquine
C. Sulfadoxine plus pyrimethamine
D. Artemether plus lumefantrine (Correct Answer)
E. Quinine plus doxycycline

Explanation: ***Artemether plus lumefantrine*** - Artemether-lumefantrine is the recommended first-line treatment for **uncomplicated P. falciparum malaria** in regions with known **chloroquine resistance**, such as North-Eastern India. - This combination therapy, an **Artemisinin-based Combination Therapy (ACT)**, is highly effective due to its rapid parasiticidal action and synergy. *Chloroquine* - Chloroquine resistance in **P. falciparum malaria** is widespread, particularly in many parts of India, including the North East. - Using chloroquine alone would likely lead to **treatment failure** and worsening of the patient's condition. *Mefloquine* - Mefloquine is an alternative treatment option, but it has significant drawbacks including **neuropsychiatric side effects** (e.g., anxiety, depression, hallucinations) and a long half-life. - It is often reserved for specific situations or as a second-line agent when ACTs are not available or contraindicated. *Sulfadoxine plus pyrimethamine* - **Sulfadoxine-pyrimethamine (SP)** is an older antimalarial drug combination that is not recommended as first-line treatment for **uncomplicated P. falciparum malaria** due to widespread **parasite resistance**. - While it was formerly used for prophylaxis and intermittent presumptive treatment, its efficacy against P. falciparum has significantly declined. *Quinine plus doxycycline* - **Quinine plus doxycycline** is an effective alternative for treating **P. falciparum malaria**, particularly in **severe cases** or when ACTs are contraindicated or unavailable. - However, it is **not the first-line treatment** for uncomplicated malaria due to longer treatment duration (7 days), more frequent dosing, and potential side effects (cinchonism, GI disturbances). - Requires adherence to a multi-day regimen, making ACTs more practical for uncomplicated cases.

Question 3: Which of the following chelating agents is indicated in iron overdose?

A. Desferrioxamine (Correct Answer)
B. BAL
C. Calcium Edetate
D. DTPA
E. Penicillamine

Explanation: ***Desferrioxamine*** - **Desferrioxamine** is a **chelate** formed by the bacterium *Streptomyces pilosus* that has a high affinity for **iron**. - It is currently the most commonly used chelating agent for **acute iron overdose** and **chronic iron overload** conditions like hemochromatosis or transfusional hemosiderosis. *BAL* - **BAL (dimercaprol)** is a chelating agent primarily used for poisoning with **arsenic**, **mercury**, and **gold**. - It works by forming stable cyclic compounds with these metals, facilitating their excretion. *Calcium Edetate* - **Calcium edetate (Calcium-EDTA)** is primarily used for **lead poisoning**. - It works by forming a stable, water-soluble complex with lead, which is then excreted by the kidneys. *DTPA* - **Diethylenetriamine pentaacetate (DTPA)** is a chelating agent primarily used for poisoning with **plutonium** and other **radioactive metals**. - It is not indicated for iron overdose. *Penicillamine* - **Penicillamine** is a chelating agent primarily used for **copper** overload (Wilson's disease) and can also be used for **lead** and **mercury** poisoning. - It is not effective for iron chelation in overdose situations.

Question 4: An 18-year-old boy from Rajasthan weighing 50 kg is diagnosed with mixed P . vivax and P . falciparum malaria. What is the appropriate treatment regimen on day 2?

A. Artesunate 50 mg (4 tablets) + Primaquine 2.5 mg ( 6 tablets)
B. Artesunate 50 mg (4 tablets) + Primaquine 7.5 mg (6 tablets)
C. Artesunate 50 mg (4 tablets) + Sulfadoxine/ pyrimethamine ( 750/37.5 mg ) (2 tablets) + Primaquine 2.5 mg ( 6 tablets) (Correct Answer)
D. Artesunate 50 mg (4 tablets) + Sulfadoxine/ pyrimethamine ( 750/37.5 mg ) (2 tablets) + Primaquine 7.5 mg ( 6 tablets)
E. Artesunate 50 mg (4 tablets) only

Explanation: ***Artesunate 50 mg (4 tablets) + Sulfadoxine/pyrimethamine (750/37.5 mg) (2 tablets) + Primaquine 2.5 mg (6 tablets)*** - For **mixed P. vivax and P. falciparum malaria**, the standard treatment regimen in India includes **Artesunate, Sulfadoxine/Pyrimethamine (SP)**, and **Primaquine**. - **Artesunate** and **SP** target the erythrocytic stages of P. falciparum, while **Primaquine** is essential for killing P. vivax hypnozoites (to prevent relapse) and P. falciparum gametocytes (to reduce transmission). - On **Day 2**, the patient continues with Artesunate along with SP (if given as single dose on Day 0, this would not be repeated; if following a specific protocol where Day 2 includes all three drugs, this represents the complete regimen). - The dosage of Primaquine of **2.5 mg** (0.25 mg/kg for 50 kg individual) daily for 14 days is appropriate for P. vivax radical cure. *Artesunate 50 mg (4 tablets) + Primaquine 2.5 mg (6 tablets)* - This regimen is incomplete for **mixed infections** as it lacks **Sulfadoxine/Pyrimethamine (SP)**, which is crucial for effective treatment of P. falciparum infections. - While Primaquine is included, the absence of SP would likely lead to treatment failure or recrudescence of **P. falciparum**. *Artesunate 50 mg (4 tablets) + Primaquine 7.5 mg (6 tablets)* - This regimen also omits **Sulfadoxine/Pyrimethamine (SP)**, which is necessary for the treatment of P. falciparum in mixed infections. - The **Primaquine dosage of 7.5 mg** is higher than typically used for P. vivax radical cure in this context (usually 0.25 mg/kg), and the absence of SP makes this regimen inadequate for mixed malaria. *Artesunate 50 mg (4 tablets) + Sulfadoxine/pyrimethamine (750/37.5 mg) (2 tablets) + Primaquine 7.5 mg (6 tablets)* - While this option includes **Artesunate** and **SP** for P. falciparum, the **Primaquine dose of 7.5 mg** is too high for the standard daily dose required for P. vivax radical cure in a 50 kg individual (which is 2.5 mg/day). - An inappropriately high dose of Primaquine for daily use for 14 days increases the risk of side effects, especially in individuals with **G6PD deficiency**, and is not the recommended regimen for mixed malaria in India. *Artesunate 50 mg (4 tablets) only* - While Artesunate is a key component of treatment, using it **alone on Day 2** without SP is inadequate for **P. falciparum** and does not address **P. vivax hypnozoites**. - This incomplete regimen would not provide radical cure for P. vivax and lacks the partner drug (SP) necessary for effective clearance of P. falciparum parasites.

Question 5: In which phase of clinical trials is drug dosing typically determined?

A. Phase 1 (Correct Answer)
B. Phase 2
C. Phase 3
D. Phase 4
E. Phase 0

Explanation: ***Phase 1*** - This phase involves a small group of **healthy volunteers** to assess the drug's safety, **pharmacokinetics (PK)**, and establish an initial dosing range. - The primary goal is to determine a **safe dosage level**, establish the **maximum tolerated dose (MTD)**, and identify potential side effects. - This is where drug dosing is **typically determined**. *Phase 0* - This is an exploratory phase involving **microdosing** studies with subtherapeutic doses. - The goal is to gather preliminary PK/PD data, but **not to determine therapeutic dosing**. *Phase 2* - This phase involves a larger group of **patients** with the condition to be treated. - The main goal is to evaluate the drug's **effectiveness** and further assess safety, but not primarily to determine initial dosing. *Phase 3* - This phase involves a large number of patients across multiple sites to confirm the drug's **efficacy** and monitor side effects in a broader population. - Dosing strategies have generally been established in earlier phases, and this phase primarily validates them. *Phase 4* - This phase occurs **after a drug has been approved** and marketed. - It involves ongoing surveillance to monitor long-term effects, collect additional information on safety, and identify new uses, but not initial dose determination.

Question 6: Which of the following statements about Ciclesonide is incorrect?

A. Oral candidiasis is common with its use. (Correct Answer)
B. It is a prodrug activated by bronchial esterase.
C. It has comparable efficacy to other inhalational corticosteroids.
D. It has fewer side effects than other inhalational corticosteroids.
E. It has low systemic bioavailability due to extensive first-pass metabolism.

Explanation: ***Oral candidiasis is common with its use.*** * Ciclesonide is a **prodrug** that is activated in the lungs, which minimizes systemic exposure and reduces the risk of local side effects like **oral candidiasis**. * Therefore, oral candidiasis is **less common** with ciclesonide compared to other inhaled corticosteroids that deliver the active drug directly to the oral cavity. *It is a prodrug activated by bronchial esterase.* * Ciclesonide is indeed a **prodrug** that is converted into its active metabolite, **des-ciclesonide**, by **esterases** primarily found in the lungs. * This specific activation mechanism helps ensure that the drug's therapeutic effects are localized to the airways while minimizing systemic exposure. *It has comparable efficacy to other inhalational corticosteroids.* * Studies have shown that ciclesonide provides **comparable efficacy** to other established inhaled corticosteroids in controlling asthma symptoms and improving lung function. * Its potent anti-inflammatory effects are effective in reducing airway hyperresponsiveness and inflammation. *It has fewer side effects than other inhalational corticosteroids.* * Because ciclesonide is a prodrug activated in the lungs and has a **high protein binding capacity**, it has a reduced likelihood of systemic side effects. * This contributes to a **favorable safety profile**, with a lower incidence of both local and systemic adverse drug reactions compared to some other inhaled corticosteroids. *It has low systemic bioavailability due to extensive first-pass metabolism.* * Ciclesonide has **very low systemic bioavailability** (<1%) when administered via inhalation. * The active metabolite des-ciclesonide that does reach systemic circulation undergoes **extensive first-pass metabolism** in the liver, further reducing systemic exposure. * This pharmacokinetic property contributes to its excellent safety profile and minimal systemic adverse effects.

Question 7: Which of the following drugs, when given with erythromycin, can cause QT prolongation and Torsades de Pointes?

A. Astemizole (Correct Answer)
B. Cetirizine
C. Loratadine
D. Promethazine
E. Fexofenadine

Explanation: ***Astemizole*** - **Astemizole** is a second-generation antihistamine that undergoes extensive metabolism by the **CYP3A4 enzyme**. - Concomitant use with **erythromycin**, a potent **CYP3A4 inhibitor**, significantly increases astemizole plasma concentrations, leading to **QT prolongation** and an elevated risk of **Torsades de Pointes**. *Cetirizine* - **Cetirizine** is another second-generation antihistamine that is primarily eliminated via **renal excretion** and does not undergo significant CYP450 metabolism. - Therefore, its co-administration with **erythromycin** does not typically lead to clinically significant drug interactions impacting cardiac repolarization. *Fexofenadine* - **Fexofenadine** is a second-generation antihistamine and active metabolite of terfenadine that is primarily eliminated via **biliary excretion** and has minimal hepatic metabolism. - While it is a substrate of **P-glycoprotein** (which can be inhibited by erythromycin), fexofenadine has a much safer cardiac profile and does not typically cause **QT prolongation** even with CYP3A4 inhibitors. *Loratadine* - **Loratadine** is a second-generation antihistamine that is metabolized by **CYP2D6** and **CYP3A4**, but its active metabolite, desloratadine, has a lower propensity for QT prolongation. - While erythromycin is a CYP3A4 inhibitor, the risk of **QT prolongation** with **loratadine** is generally considered much lower than with astemizole, even with concurrent use. *Promethazine* - **Promethazine** is a first-generation antihistamine and phenothiazine derivative that primarily acts as a **dopamine D2 receptor antagonist**. - While it can cause **QT prolongation** on its own at high doses, its metabolism is complex and not predominantly dependent on **CYP3A4** to the extent that interaction with **erythromycin** poses the same severe risk as with astemizole.

Question 8: Which of the following is an inclusion criterion for the shorter bedaquiline regimen in the treatment of tuberculosis?

A. Extrapulmonary TB like Tubercular meningitis
B. Rifampicin resistance with both KatG and inhA mutation
C. Rifampicin-sensitive TB
D. Rifampicin-resistant but fluoroquinolone-sensitive TB (Correct Answer)
E. Extensively drug-resistant TB (XDR-TB)

Explanation: ***Rifampicin-resistant but fluoroquinolone-sensitive TB*** - The **shorter bedaquiline regimen** is specifically recommended for patients with **rifampicin-resistant tuberculosis** who are also sensitive to fluoroquinolones. - This regimen optimizes treatment outcomes by leveraging the effectiveness of both bedaquiline and a potent fluoroquinolone against sensitive strains. *Extrapulmonary TB like Tubercular meningitis* - The shorter bedaquiline regimen is generally not recommended for severe forms of **extrapulmonary TB**, especially those involving the **central nervous system**, due to concerns about drug penetration and efficacy. - These cases often require longer, individualized regimens with stronger central nervous system penetration. *Rifampicin resistance with both KatG and inhA mutation* - The presence of both **KatG** and **inhA mutations** indicates high-level **isoniazid resistance**, which is not the primary criterion for selecting the shorter bedaquiline regimen. - While these mutations are important for guiding isoniazid use, the core inclusion for this regimen is **rifampicin resistance** and **fluoroquinolone sensitivity**. *Rifampicin-sensitive TB* - Patients with **rifampicin-sensitive TB** are usually treated with standard first-line regimens that do not include bedaquiline, as their disease is susceptible to more conventional therapies. - The shorter bedaquiline regimen is reserved for drug-resistant cases, particularly those with rifampicin resistance. *Extensively drug-resistant TB (XDR-TB)* - While **XDR-TB** patients may receive bedaquiline, they typically require **longer, individualized regimens** rather than the shorter standardized regimen. - The shorter bedaquiline regimen is primarily indicated for **rifampicin-resistant TB** that is **fluoroquinolone-sensitive**, whereas XDR-TB involves resistance to both fluoroquinolones and injectable agents, requiring more complex treatment approaches.

Question 9: Aprepitant is a drug used in the treatment of some cases of chemotherapy-induced nausea and vomiting. What is the mechanism of action of this drug?

A. NK1 antagonist (Correct Answer)
B. NK3 antagonist
C. NK1 agonist
D. NK2 agonist
E. NK2 antagonist

Explanation: ***NK1 antagonist*** - **Aprepitant** is a selective, high-affinity antagonist of the **neurokinin 1 (NK1) receptor**, which is activated by **substance P**. - By blocking NK1 receptors in the brainstem's **vomiting center**, aprepitant prevents nausea and vomiting, especially in chemotherapy-induced cases. - Aprepitant is particularly effective for **acute and delayed** chemotherapy-induced nausea and vomiting (CINV). *NK3 antagonist* - While **neurokinin 3 (NK3) receptors** are present in the central nervous system, their specific role in chemotherapy-induced nausea and vomiting is less prominent. - Aprepitant does not primarily target NK3 receptors; its antiemetic action is mediated through NK1 blockade. *NK1 agonist* - An **NK1 agonist** would activate the NK1 receptor, potentially *inducing* nausea and vomiting, which is the opposite of the desired therapeutic effect of aprepitant. - Agonists are typically used to stimulate a receptor, not block it as is done with aprepitant. *NK2 antagonist* - **Neurokinin 2 (NK2) receptors** are also part of the tachykinin receptor family, but they are not the primary target for antiemetic drugs like aprepitant. - While NK2 receptors play roles in smooth muscle contraction and inflammation, blocking them is not the mechanism by which aprepitant prevents nausea and vomiting. - Aprepitant's antiemetic efficacy is specifically due to **NK1 receptor antagonism**. *NK2 agonist* - **Neurokinin 2 (NK2) receptors** are also part of the tachykinin receptor family, but they are not the primary target for antiemetic drugs like aprepitant. - Activating NK2 receptors would not provide the antiemetic effect seen with aprepitant, as NK1 receptor antagonism is crucial.

Question 10: Methotrexate use causes reduced synthesis of which of the following?

A. TMP (Correct Answer)
B. CMP
C. GMP
D. AMP
E. UMP

Explanation: ***TMP (Thymidylate)*** - Methotrexate is a **folate analog** that inhibits **dihydrofolate reductase (DHFR)**, preventing the regeneration of tetrahydrofolate (THF) from dihydrofolate. - **Tetrahydrofolate** is essential for **thymidylate synthase**, which converts dUMP to **TMP (thymidylate)** - this is the **most directly and significantly affected** nucleotide synthesis pathway. - Reduced TMP synthesis leads to impaired DNA synthesis and is the **primary mechanism** of methotrexate's cytotoxic effects. *CMP (Cytidine monophosphate)* - CMP synthesis occurs via the **de novo pyrimidine pathway** starting from carbamoyl phosphate and aspartate, forming UMP, which is then converted to CMP. - This pathway **does not require tetrahydrofolate** cofactors, so methotrexate does not significantly affect CMP synthesis directly. *GMP (Guanosine monophosphate)* - GMP is a purine nucleotide whose synthesis **does require tetrahydrofolate** derivatives (N10-formyl-THF) at two steps in the de novo purine pathway. - However, the effect on GMP is **less direct and less pronounced** than on TMP synthesis, and cells can partially compensate through salvage pathways. *AMP (Adenosine monophosphate)* - AMP is also a purine nucleotide that requires **N10-formyl-THF** cofactors during de novo synthesis (same pathway branch point as GMP). - Like GMP, it is affected but **less directly than TMP**, and salvage pathways provide alternative synthesis routes. *UMP (Uridine monophosphate)* - UMP is synthesized through the **de novo pyrimidine pathway** which does not require folate cofactors. - Methotrexate does not inhibit the enzymes (carbamoyl phosphate synthetase II, aspartate transcarbamoylase, dihydroorotase, etc.) involved in UMP synthesis.

Question 11: Which of the following are toxic metabolites associated with methanol poisoning?

A. Formic acid + Oxalic acid
B. Formic acid + Lactic acid (Correct Answer)
C. Glycolic acid + Oxalic acid
D. Oxalic acid + Lactic acid
E. Hippuric acid + Formic acid

Explanation: ***Formic acid + Lactic acid*** - **Methanol** is metabolized in the body into **formaldehyde** and then to **formic acid**, which is primarily responsible for its toxicity. - While not a direct derivative, **lactic acid** levels often rise significantly in severe methanol poisoning due to **hypoxia** and **metabolic acidosis** caused by formic acid-induced mitochondrial dysfunction. *Formic acid + Oxalic acid* - **Formic acid** is indeed a toxic metabolite of methanol, but **oxalic acid** is not. - **Oxalic acid** is a toxic metabolite of **ethylene glycol** poisoning, not methanol. *Glycolic acid + Oxalic acid* - Neither **glycolic acid** nor **oxalic acid** are toxic metabolites of methanol. - Both **glycolic acid** and **oxalic acid** are associated with **ethylene glycol** poisoning. *Oxalic acid + Lactic acid* - **Oxalic acid** is not a derivative of methanol poisoning. - While **lactic acid** can be elevated in methanol poisoning, its combination with oxalic acid is incorrect for methanol metabolites. *Hippuric acid + Formic acid* - **Formic acid** is correct, but **hippuric acid** is not a metabolite of methanol. - **Hippuric acid** is a metabolite of **toluene** and is used as a urinary marker for toluene exposure.

Question 12: Phenobarbitone exerts its therapeutic effect primarily through which mechanism?

A. Enhancement of GABA-A receptor function (Correct Answer)
B. Voltage-gated sodium channel blockade
C. Voltage-gated calcium channel blockade
D. Potassium channel opening
E. NMDA receptor antagonism

Explanation: ***Enhancement of GABA-A receptor function*** - **Phenobarbitone** (phenobarbital) is a barbiturate that acts primarily by **enhancing GABA-A receptor activity** - It binds to a distinct **barbiturate binding site** on the GABA-A receptor complex - This binding **prolongs the duration of chloride channel opening** in response to GABA - Results in increased **chloride ion influx**, neuronal **hyperpolarization**, and **decreased neuronal excitability** - This mechanism underlies its **anticonvulsant** and **sedative-hypnotic** properties *NMDA receptor antagonism* - While some anticonvulsants work through NMDA receptor antagonism (e.g., ketamine, felbamate), this is **not the primary mechanism** of phenobarbitone *Voltage-gated sodium channel blockade* - Sodium channel blockade is the mechanism of action for drugs like **phenytoin, carbamazepine**, and **lamotrigine** - Phenobarbitone does not significantly block sodium channels at therapeutic concentrations *Voltage-gated calcium channel blockade* - Calcium channel blockers like **ethosuximide** (T-type) and **gabapentin** (α2δ subunit) work through this mechanism - This is not the primary mechanism for phenobarbitone *Potassium channel opening* - Potassium channel openers like **retigabine** increase potassium conductance - Phenobarbitone does not primarily work through this mechanism

Question 13: A patient on multidrug therapy (MBMDT) for leprosy presents with inflammation over preexisting lesions and nerve involvement. What is the best approach for treatment?

A. Continue anti-leprosy treatment (ALT) and start thalidomide
B. Continue anti-leprosy treatment (ALT) and start steroids (Correct Answer)
C. Stop anti-leprosy treatment (ALT) and start thalidomide
D. Stop anti-leprosy treatment (ALT) and start steroids
E. Stop anti-leprosy treatment (ALT) temporarily and reassess

Explanation: ***Continue anti-leprosy treatment (ALT) and start steroids*** - The patient is experiencing a **type 1 leprosy reaction (reversal reaction)**, characterized by inflammation over existing lesions and nerve involvement, which requires immediate immunosuppression with **steroids**. - **Anti-leprosy treatment (ALT)** must be continued as the reaction is an immunological phenomenon independent of the ongoing bacterial eradication and stopping it could lead to relapse. *Continue anti-leprosy treatment (ALT) and start thalidomide* - **Thalidomide** is primarily used for **type 2 leprosy reactions (erythema nodosum leprosum, ENL)**, which present with new, painful, tender nodules, fever, and systemic symptoms, not typically aggravated pre-existing lesions and nerve involvement. - While ALT is correctly continued, thalidomide is not the first-line treatment for a type 1 reaction due to its specific indication for ENL. *Stop anti-leprosy treatment (ALT) and start thalidomide* - **Stopping ALT** is incorrect as it can lead to **relapse** of leprosy and development of **drug resistance**. - **Thalidomide** is not indicated for type 1 leprosy reactions, making this approach inappropriate. *Stop anti-leprosy treatment (ALT) and start steroids* - While **steroids** are the correct treatment for **type 1 leprosy reactions**, **stopping ALT** is a critical error that can have severe consequences for the patient's leprosy management. - The reaction is an immune response to dead or dying bacilli, not a failure of ALT, so treatment should be completed. *Stop anti-leprosy treatment (ALT) temporarily and reassess* - **Temporarily stopping ALT** is incorrect even during a leprosy reaction, as reactions are immune-mediated responses to treatment, not adverse drug effects requiring cessation. - Interrupting treatment can lead to **incomplete bacterial eradication**, **relapse**, and potential **drug resistance**; the standard approach is to continue ALT while managing the reaction with immunosuppression.

Question 14: A patient is taking metronidazole for anaerobic infection. Which of the following should be avoided during this period

A. Colchicine
B. Alcohol (Correct Answer)
C. Rifampicin
D. Ciprofloxacin
E. Warfarin

Explanation: ***Alcohol*** - Metronidazole inhibits **aldehyde dehydrogenase**, an enzyme responsible for metabolizing alcohol, leading to an accumulation of **acetaldehyde**. - This accumulation causes a **disulfiram-like reaction**, characterized by flushing, nausea, vomiting, headache, and palpitations, making alcohol avoidance crucial. *Colchicine* - Colchicine is used for gout and **familial Mediterranean fever**; there's no major contraindicated interaction with metronidazole. - While both can cause gastrointestinal side effects, combining them does not typically lead to a life-threatening interaction or necessitate avoidance. *Rifampicin* - Rifampicin is a potent **CYP450 enzyme inducer** and can decrease the effectiveness of many drugs, including metronidazole, by increasing its metabolism. - While an interaction exists, it typically involves reduced metronidazole efficacy rather than a strict contraindication requiring complete avoidance. *Ciprofloxacin* - Ciprofloxacin is a **quinolone antibiotic** and generally does not have a clinically significant, contraindicated interaction with metronidazole. - Both can individually cause **gastrointestinal side effects**, but their co-administration is not generally discouraged due to synergy in treatment or increased toxicity. *Warfarin* - Metronidazole can enhance the anticoagulant effect of warfarin by inhibiting its metabolism, potentially increasing **INR** and bleeding risk. - However, this interaction is **manageable with monitoring**; warfarin is not absolutely contraindicated and can be used with dose adjustments and frequent INR checks, unlike alcohol which must be completely avoided.

Question 15: A patient on digoxin therapy presents with atrial fibrillation and controlled ventricular rate. Upon evaluation, the patient's serum digoxin levels are elevated compared to previous values. Which of the following concomitant medications is most likely to have contributed to the enhanced digoxin toxicity?

A. Triamterene
B. KCL
C. Atenolol
D. Clarithromycin (Correct Answer)
E. Amiodarone

Explanation: ***Clarithromycin*** - **Clarithromycin** is a **macrolide antibiotic** known to inhibit the cytochrome P450 3A4 (CYP3A4) enzyme system and **P-glycoprotein**. - This inhibition leads to decreased metabolism and **efflux of digoxin**, resulting in **increased serum digoxin levels** and enhanced toxicity. - Among the options, clarithromycin is the **most common cause** of elevated digoxin levels through P-gp inhibition. *Triamterene* - **Triamterene** is a **potassium-sparing diuretic** that can increase serum potassium. - **Hyperkalemia** generally *reduces* the binding of digoxin to Na+/K+-ATPase, thereby potentially *reducing* its toxic effects. - Does not significantly affect digoxin serum levels. *KCL* - **Potassium chloride (KCl)** is used to correct **hypokalemia**. - **Hypokalemia** can *potentiate* digoxin toxicity because low potassium increases digoxin binding to the Na+/K+-ATPase pump. - However, KCl supplementation *corrects* hypokalemia and would actually *reduce* toxicity risk, not increase serum digoxin levels. *Atenolol* - **Atenolol** is a **beta-blocker** primarily used to control heart rate and blood pressure. - While it can slow the heart rate like digoxin (additive pharmacodynamic effect), it does not significantly alter the **pharmacokinetics** or serum levels of digoxin. *Amiodarone* - **Amiodarone** is an **antiarrhythmic** that can inhibit P-glycoprotein and increase digoxin levels. - However, in this scenario, **clarithromycin** is more commonly associated with acute elevations in digoxin levels in clinical practice. - Amiodarone interactions are well-known and typically require dose adjustments at initiation.

Question 16: Which antitubercular drug reduces the efficacy of oral contraceptive pills (OCPs)?

A. Rifampicin (Correct Answer)
B. Isoniazid
C. Ethambutol
D. Pyrazinamide
E. Streptomycin

Explanation: ***Rifampicin*** - **Rifampicin** is a potent inducer of **cytochrome P450 enzymes**, particularly CYP3A4, which metabolize oral contraceptive pills (OCPs). - This increased metabolism leads to lower systemic levels of contraceptive hormones, reducing their efficacy and increasing the risk of **unintended pregnancy**. - Women on Rifampicin should use **additional barrier contraception** or alternative contraceptive methods. *Isoniazid* - **Isoniazid** is primarily metabolized by N-acetyltransferase and cytochrome P450, but it is not a significant enzyme inducer. - It does not typically interfere with the effectiveness of **oral contraceptive pills**. *Ethambutol* - **Ethambutol** is eliminated largely unchanged via renal excretion and is not a significant inducer or inhibitor of cytochrome P450 enzymes. - It does not interact with **oral contraceptive pills**. *Pyrazinamide* - **Pyrazinamide** is metabolized by the liver, but it does not significantly induce or inhibit the cytochrome P450 system involved in OCP metabolism. - It is not known to reduce the effectiveness of **oral contraceptive pills**. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic that is not metabolized by the liver and does not affect cytochrome P450 enzymes. - It has no interaction with **oral contraceptive pills**.

Question 17: What is the mechanism of action of Methotrexate?

A. Inhibition of Dihydrofolate reductase (Correct Answer)
B. Inhibits pyrimidine synthesis
C. Inhibits cell replication by acting on G phase of cell cycle
D. Inhibits Thymidylate synthase
E. Inhibits RNA polymerase

Explanation: ***Inhibition of Dihydrofolate reductase*** - **Methotrexate** is a **folate analog** that competitively inhibits **dihydrofolate reductase (DHFR)**, an enzyme essential for converting **dihydrofolate** to **tetrahydrofolate**. - This inhibition blocks the synthesis of **purines** and **pyrimidines**, thereby preventing DNA and RNA synthesis and ultimately inhibiting cell proliferation. *Inhibits pyrimidine synthesis* - While methotrexate ultimately inhibits pyrimidine synthesis by depleting tetrahydrofolate, its direct mechanism is not the inhibition of the pyrimidine synthesis pathway enzymes themselves. - Its primary action is upstream, by inhibiting DHFR. *Inhibits cell replication by acting on G phase of cell cycle* - Methotrexate primarily inhibits cells in the **S-phase** of the cell cycle, as it interferes with DNA synthesis. - It does not specifically target the G phase; rather, it affects cells that are actively attempting to replicate their DNA. *Inhibits Thymidylate synthase* - **Thymidylate synthase** is inhibited by drugs like **5-fluorouracil**, which directly blocks the conversion of **deoxyuridine monophosphate (dUMP)** to **deoxythymidine monophosphate (dTMP)**. - Methotrexate's effect on thymidylate synthesis is indirect, mediated by the depletion of the cofactor **N5,N10-methylene-tetrahydrofolate** due to DHFR inhibition. *Inhibits RNA polymerase* - **RNA polymerase** inhibition is the mechanism of drugs like **rifampin** (bacterial RNA polymerase) and **α-amanitin** (eukaryotic RNA polymerase). - Methotrexate does not directly inhibit RNA polymerase; its effects on RNA synthesis are secondary to depletion of nucleotide precursors through DHFR inhibition.

Question 18: What is the mechanism of action of Tocilizumab?

A. TNF Alpha inhibition
B. IL-18 inhibition
C. Inhibits binding of IL-6 to its receptor IL-6R (Correct Answer)
D. Inhibits binding of IL-1
E. IL-17 inhibition

Explanation: ***Inhibits binding of IL-6 to its receptor IL-6R*** - **Tocilizumab** is a **monoclonal antibody** that specifically targets the **interleukin-6 (IL-6) receptor**. - By blocking IL-6 from binding to its receptor, Tocilizumab **inhibits IL-6 mediated signaling**, thereby reducing inflammation and immune responses. *TNF Alpha inhibition* - **TNF-alpha inhibitors** (e.g., adalimumab, infliximab) target **tumor necrosis factor-alpha**, a different pro-inflammatory cytokine. - While both TNF-alpha and IL-6 are involved in inflammatory diseases, their signaling pathways and therapeutic targets are distinct. *IL-18 inhibition* - **IL-18** is another pro-inflammatory cytokine, but Tocilizumab does **not directly target** or inhibit its activity. - Drugs that target IL-18 or its pathways are distinct from those targeting IL-6. *IL-17 inhibition* - **IL-17 inhibitors** (e.g., secukinumab, ixekizumab) are biologics that target **interleukin-17**, particularly useful in psoriasis and ankylosing spondylitis. - Tocilizumab's mechanism is specific to **IL-6**, not IL-17. *Inhibits binding of IL-1* - **Interleukin-1 (IL-1)** is a key mediator of inflammation, but specific **IL-1 inhibitors** (e.g., anakinra, canakinumab) act by blocking IL-1 or its receptor. - Tocilizumab's mechanism is specific to the **IL-6 cytokine-receptor interaction**, not IL-1.

Question 19: After receiving a positive newborn screening result, a 2-week-old male infant is brought to the pediatrician for a diagnostic sweat test. The results demonstrated chloride levels of 65 mmol/L (nl < 29 mmol/L). Subsequent DNA sequencing revealed a 3 base pair deletion in a transmembrane cAMP-activated ion channel known to result in protein instability and early degradation. The physician discusses with the parents that the infant will develop respiratory infections due to improper mucus clearance and reviews various mucolytic agents, such as one that cleaves disulfide bonds between mucus glycoproteins thereby loosening the mucus plug. This mucolytic can also be used as a treatment for which of the following overdoses?

A. Cyanide
B. Acetaminophen (Correct Answer)
C. Salicylates
D. Benzodiazepines
E. Opioids

Explanation: ***Acetaminophen*** - The mucolytic described is **N-acetylcysteine (NAC)**, which functions by cleaving **disulfide bonds** in mucus glycoproteins. - NAC is also the antidote for **acetaminophen overdose**, as it replenishes **glutathione stores**, which are crucial for detoxifying acetaminophen metabolites. *Cyanide* - Cyanide poisoning is typically treated with agents like **amyl nitrite**, **sodium nitrite**, and **sodium thiosulfate**. - These treatments work by inducing methemoglobinemia or directly binding to cyanide to facilitate its excretion. *Salicylates* - Salicylate (aspirin) overdose is primarily managed with **alkalinization of the urine** (using sodium bicarbonate) and **hemodialysis**. - These methods enhance salicylate elimination. *Benzodiazepines* - Benzodiazepine overdose is treated with **flumazenil**, a **GABA receptor antagonist**, which reverses the central nervous system depression. - NAC has no role in reversing the effects of benzodiazepines. *Opioids* - Opioid overdose is treated with **naloxone**, an **opioid receptor antagonist**, which rapidly reverses respiratory depression and other opioid effects. - NAC does not interact with the opioid system.

Question 20: A 36-year-old woman with no significant medical history presents with a four-week history of epigastric pain. The pain tends to occur two hours after meals. She has lost 4 pounds over the last four weeks. She is allergic to azithromycin and clarithromycin. A urea breath test detects radiolabeled carbon dioxide in exhaled breath. Two days after starting definitive treatment, she returns to the hospital with flushing, headaches, nausea and vomiting after having a few beers that night. What is the mechanism of the drug involved in the adverse reaction?

A. Inhibition of aldehyde dehydrogenase (Correct Answer)
B. Coating of the gastric lining
C. Inhibition of H+/K+ ATPase in parietal cells
D. Binding to the 30S subunit of the ribosome
E. Binding to the 50S subunit of the ribosome

Explanation: ***Inhibition of aldehyde dehydrogenase*** - The patient's symptoms (flushing, headaches, nausea, vomiting) after consuming alcohol are characteristic of a **disulfiram-like reaction**. This occurs when a drug inhibits **aldehyde dehydrogenase**, leading to an accumulation of acetaldehyde, a toxic metabolite of alcohol. - Given the patient's positive urea breath test, she was likely diagnosed with *Helicobacter pylori* infection and was undergoing eradication therapy. In this scenario, **metronidazole** is often used in regimens, especially when macrolide allergies (azithromycin, clarithromycin) are present, and it is known to cause a disulfiram-like reaction by inhibiting aldehyde dehydrogenase. *Coating of the gastric lining* - This is the mechanism of action of **sucralfate**, a drug used to treat peptic ulcers by forming a protective barrier over the ulcer surface. - Sucralfate does not interact with alcohol to cause systemic adverse reactions like flushing or nausea and vomiting. *Inhibition of H+/K+ ATPase in parietal cells* - This is the mechanism of action of **proton pump inhibitors (PPIs)** like omeprazole or pantoprazole, which are commonly used in *H. pylori* eradication regimens to reduce gastric acid production. - PPIs do not cause a disulfiram-like reaction with alcohol. *Binding to the 30S subunit of the ribosome* - This is the mechanism of action of **tetracycline antibiotics** (e.g., doxycycline), which are sometimes used in *H. pylori* eradication regimens. - While tetracyclines can have various side effects, they do not cause a disulfiram-like reaction when combined with alcohol. *Binding to the 50S subunit of the ribosome* - This is the mechanism of action for **macrolide antibiotics** (like azithromycin, clarithromycin) and **chloramphenicol**. The patient is allergic to macrolides, ruling them out for primary treatment. - Although chloramphenicol can cause a disulfiram-like reaction, its use in *H. pylori* infection is not standard practice, and macrolides do not typically cause this reaction.

Question 21: A 4-year-old boy is brought by his mother to the emergency room for malaise, dizziness, and sleepiness. The mother owns a dry cleaning shop and found her son in the back room with an open canister of carbon tetrachloride, one of their cleaning fluids. The boy reports feeling nauseous and has a mild headache. He has a history of spastic hemiplegic cerebral palsy and is seen regularly by a pediatric neurologist. He is otherwise healthy and takes no medications. His temperature is 98.6°F (37°C), blood pressure is 105/55 mmHg, pulse is 105/min, and respirations are 22/min. On exam, he appears tired and drowsy but is able to answer questions. He has increased tone in his left upper and lower extremities. Which of the following is most likely to be affected by this patient's exposure to the dry cleaning fluid?

A. Bone marrow
B. Myocardium
C. Hepatocytes (Correct Answer)
D. Lung parenchyma
E. Gastric mucosa

Explanation: ***Hepatocytes*** - **Carbon tetrachloride (CCl4)** is a potent **hepatotoxin** that is bioactivated in the liver by cytochrome P450 enzymes, leading to the formation of free radicals and subsequent **lipid peroxidation** and **hepatocellular necrosis**. - Exposure to CCl4, commonly found in dry cleaning fluids, results in significant liver damage, manifesting as symptoms like nausea, malaise, and dizziness, with potential progression to liver failure. *Bone marrow* - While some toxins can affect bone marrow, such as benzene or certain chemotherapeutic agents, **carbon tetrachloride** is not primarily known for causing **bone marrow suppression** or hematological disorders. - The symptoms described do not point to bone marrow dysfunction; instead, they align with acute toxic exposure affecting other organ systems. *Myocardium* - Although high doses of carbon tetrachloride can potentially induce cardiac arrhythmias or myocardial damage, it is **not the primary target organ** for acute CCl4 toxicity. - **Dizziness** and **sleepiness** are more indicative of central nervous system involvement or general malaise rather than direct myocardial injury. *Lung parenchyma* - Inhalation of carbon tetrachloride vapors can cause **respiratory irritation** and, in severe cases, pulmonary edema, but **it is not the main organ system affected** by CCl4 poisoning. - The presented symptoms of malaise, dizziness, and nausea are not typical primary manifestations of isolated lung parenchyma injury from CCl4. *Gastric mucosa* - While ingestion of CCl4 could cause **gastrointestinal irritation** and symptoms like nausea, the gastric mucosa is **not the main target organ responsible for the systemic toxicity** observed in CCl4 poisoning. - The overall clinical picture, especially given the history of exposure to an industrial solvent, points more definitively to systemic organ damage, particularly hepatic.

Question 22: A 2-week-old boy presents to the pediatrics clinic. The medical records note a full-term delivery, however, the boy was born with chorioretinitis and swelling and calcifications in his brain secondary to an in utero infection. In immunocompromised patients, a drug can be used for prophylaxis against the pathogen responsible for this neonate's findings. This same drug also provides protection against which other microorganism?

A. Pneumocystis jirovecii (Correct Answer)
B. Mycobacterium tuberculosis
C. Cryptococcus neoformans
D. Mycobacterium avium complex
E. Cytomegalovirus

Explanation: ***Pneumocystis jirovecii*** - The neonate's symptoms of **chorioretinitis**, **intracranial calcifications**, and **brain swelling** are characteristic of congenital **toxoplasmosis**, caused by *Toxoplasma gondii*. - In **immunocompromised patients** (especially those with HIV/AIDS and CD4 counts <100 cells/μL), **trimethoprim-sulfamethoxazole (TMP-SMX)** is used for dual prophylaxis against both *Toxoplasma gondii* and ***Pneumocystis jirovecii***. - TMP-SMX is the **primary prophylactic agent** for *Pneumocystis jirovecii* pneumonia (PCP) and also provides effective protection against toxoplasmic encephalitis in this population. *Mycobacterium tuberculosis* - Tuberculosis prophylaxis primarily involves **isoniazid (INH)** or **rifampin**, not TMP-SMX. - TB does not present with congenital chorioretinitis or diffuse intracranial calcifications. *Cryptococcus neoformans* - Prophylaxis for cryptococcosis in immunocompromised patients typically involves **fluconazole**, not TMP-SMX. - Cryptococcal disease primarily causes meningitis and pulmonary disease in HIV/AIDS patients. *Mycobacterium avium complex* - MAC prophylaxis is typically with **azithromycin** or **clarithromycin**, not TMP-SMX. - MAC infection presents with disseminated disease (fever, weight loss, anemia) in advanced HIV/AIDS, not congenital findings. *Cytomegalovirus* - While CMV can cause similar congenital findings (chorioretinitis and periventricular calcifications), CMV prophylaxis involves **ganciclovir** or **valganciclovir**, not TMP-SMX. - TMP-SMX does not provide protection against CMV.

Question 23: At 10 a.m. this morning, a semi-truck carrying radioactive waste toppled over due to a blown tire. One container was damaged, and a small amount of its contents leaked into the nearby river. You are a physician on the government's hazardous waste committee and must work to alleviate the town's worries and minimize the health hazards due to the radioactive leak. You decide to prescribe a prophylactic agent to minimize any retention of radioactive substances in the body. Which of the following do you prescribe?

A. Potassium iodide (Correct Answer)
B. EDTA
C. Methylene blue
D. Vitamin C
E. Succimer

Explanation: ***Potassium iodide*** - **Potassium iodide (KI)** is used to block the uptake of **radioactive iodine** by the **thyroid gland**, preventing it from causing thyroid cancer. - This is a crucial prophylactic measure when there's a risk of exposure to radioactive iodine, which is a common component of nuclear waste. *EDTA* - **EDTA (Ethylenediaminetetraacetic acid)** is a **chelating agent** used to treat **heavy metal poisoning**, such as lead poisoning. - It works by binding to metal ions in the body, facilitating their excretion, but it is not effective against radioactive iodine. *Methylene blue* - **Methylene blue** is primarily used as an antidote for **methemoglobinemia**, a condition where the iron in hemoglobin is oxidized, reducing its oxygen-carrying capacity. - It also has applications in diagnosing certain medical conditions and as an antiseptic but has no role in preventing radioactive iodine uptake. *Vitamin C* - **Vitamin C (ascorbic acid)** is an essential vitamin and a powerful **antioxidant**, important for immune function, collagen synthesis, and protecting cells from oxidative damage. - It does not have any known protective action against the absorption or effects of radioactive substances. *Succimer* - **Succimer (DMSA)** is another **chelating agent** specifically approved for the treatment of **lead poisoning** in children and other heavy metal poisoning. - While effective for heavy metal chelation, it does not prevent the uptake of radioactive iodine by the thyroid.

Question 24: A 45-year-old woman presents to the emergency department with fever, cough, tonsillar enlargement, and bleeding lips. She has a diffuse blistering rash that encompasses the palms and soles of her feet, in total covering 55% of her total body surface area (TBSA). The upper epidermal layer easily slips away with slight rubbing. Within 24 hours the rash progresses to 88% TBSA involvement and the patient requires mechanical ventilation for respiratory distress. Which of the following is the most likely etiology of this patient’s condition?

A. Cytomegalovirus
B. Deficiency of C-1 esterase inhibitor
C. Exposure to carbamazepine (Correct Answer)
D. Herpes simplex virus
E. Molluscum contagiosum

Explanation: ***Exposure to carbamazepine*** - The rapid progression of a widespread blistering rash, **positive Nikolsky's sign** (skin slipping away), significant TBSA involvement (55% rapidly increasing to 88%), and systemic symptoms (fever, respiratory distress) are highly characteristic of **Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN)**. - **Carbamazepine** is a well-known medication trigger for SJS/TEN, a severe cutaneous adverse drug reaction. *Cytomegalovirus* - While CMV can cause a rash and systemic symptoms, it typically manifests as a **maculopapular rash** or purpura, not extensive blistering with a positive Nikolsky's sign. - CMV infection usually presents with features like mononucleosis-like syndrome, hepatitis, or retinitis, which are not described here as the primary concern. *Deficiency of C-1 esterase inhibitor* - This deficiency causes **hereditary angioedema**, characterized by recurrent episodes of localized swelling, typically affecting the face, airways, and gastrointestinal tract. - It does not cause a blistering rash or the extensive epidermal detachment seen in this patient. *Herpes simplex virus* - HSV can cause blistering lesions, but these are typically **localized vesicles** that progress to ulcers, such as cold sores or genital herpes. - While widespread HSV infection can occur in immunocompromised patients, it does not typically present as a diffuse blistering rash with such extensive epidermal detachment and high TBSA involvement as described. *Molluscum contagiosum* - This is a viral skin infection that causes characteristic **dome-shaped, umbilicated papules**. - It does not cause a widespread blistering rash, fever, or the severe systemic symptoms and epidermal detachment seen in this patient.

Question 25: A 28-year-old man comes to the physician for the evaluation of a progressively worsening tremor in his hands and multiple falls over the past 3 months. The tremor occurs both at rest and with movement. He also reports decreased concentration and a loss of interest in his normal activities over this time period. He has no history of serious medical illness and takes no medications. He drinks two alcoholic beverages daily and does not use illicit drugs. Vital signs are within normal limits. Physical exam shows mild jaundice, a flapping tremor, and a broad-based gait. Serum studies show: Aspartate aminotransferase 554 U/L Hepatitis B surface antibody positive Hepatitis B surface antigen negative Ceruloplasmin 5.5 mg/dL (normal: 19.0-31.0 mg/dL) Which of the following is the most appropriate pharmacotherapy for this patient?

A. Penicillamine (Correct Answer)
B. Levodopa
C. Prednisolone
D. Deferoxamine
E. Tenofovir

Explanation: ***Penicillamine*** - This patient presents with symptoms and lab findings suggestive of **Wilson's disease**, including a **progressively worsening tremor** (both rest and action), **gait ataxia**, **neuropsychiatric symptoms** (decreased concentration, loss of interest), **jaundice**, **elevated AST**, and a **markedly low ceruloplasmin level**. - **Penicillamine** is a copper chelating agent that promotes the excretion of copper and is an established treatment for Wilson's disease. - Note: While penicillamine has been historically used as first-line therapy, current guidelines often favor **trientine or zinc** due to better side effect profiles, particularly in neurologic presentations. However, penicillamine remains a valid therapeutic option among the choices provided. *Levodopa* - **Levodopa** is a precursor to dopamine and is the primary treatment for **Parkinson's disease**, which typically presents with a rest tremor, bradykinesia, rigidity, and postural instability. - While this patient has a tremor, his young age, liver involvement, and low ceruloplasmin point away from Parkinson's disease. *Prednisolone* - **Prednisolone** is a corticosteroid used as an anti-inflammatory and immunosuppressant, effective in treating conditions like autoimmune hepatitis or inflammatory bowel disease. - It does not address the underlying **copper accumulation** in Wilson's disease, and the patient's presentation does not primarily suggest an autoimmune inflammatory process. *Deferoxamine* - **Deferoxamine** is an iron chelating agent used to treat **iron overload (hemochromatosis)**, typically caused by conditions like multiple blood transfusions or a genetic predisposition. - This patient's symptoms and labs, particularly the low ceruloplasmin, do not indicate iron overload. *Tenofovir* - **Tenofovir** is an antiviral medication primarily used to treat **chronic hepatitis B** or HIV. - While the patient has elevated AST and a history of hepatitis B exposure (indicated by positive surface antibody), his surface antigen is negative, meaning he is not currently infected with active hepatitis B, and his severe neurologic symptoms point to another diagnosis.

Question 26: A 56-year-old woman comes to the physician with a 6-month history of black spots in her vision. She has been unable to drive at night for the past 4 months. The patient has rheumatoid arthritis, type 2 diabetes mellitus, and depression. Her mother has glaucoma. She has never smoked. She drinks one or two glasses of homemade moonshine every day after dinner. Current medications include metformin, citalopram, and chloroquine. She is 168 cm (5 ft 6 in) tall and weighs 79 kg (174 lb); BMI is 28 kg/m2. Her temperature is 36.8°C (98.2°F), pulse is 68/min, and blood pressure is 138/83 mm Hg. Examination shows swan neck deformities of both hands. The patient's vision is 20/20 in both eyes. She has difficulty adapting to changes in lighting in both eyes. Slit lamp examination shows a normal anterior segment. The posterior segment shows bilateral bull's eye macular lesions. Hemoglobin 11.7 g/dL Mean corpuscular volume 98 μm3 Serum Alkaline phosphatase 65 U/L Aspartate aminotransferase (AST, GOT) 20 U/L Alanine aminotransferase (ALT, GPT) 17 U/L γ-Glutamyltransferase (GGT) 90 U/L (N=5–50 U/L) Which of the following is the most likely cause of this patient's symptoms?

A. Angle-closure glaucoma
B. Age-related macular degeneration
C. Chloroquine retinopathy (Correct Answer)
D. Diabetic retinopathy
E. Methanol toxicity

Explanation: ***Chloroquine retinopathy*** - The presence of **bilateral bull's eye macular lesions** is a classic and highly specific finding for **chloroquine (or hydroxychloroquine) toxicity**. - **Chloroquine** is known to cause dose-dependent retinopathy, leading to **vision changes** like black spots and difficulty with **night vision** as described. *Angle-closure glaucoma* - This condition presents with **sudden severe eye pain**, blurred vision, and a **mid-dilated pupil**, which are not reported here. - While visual symptoms can occur, **bull's eye maculopathy** is not a feature of glaucoma; glaucoma primarily causes **optic nerve damage** and peripheral vision loss. *Age-related macular degeneration* - This typically presents with **gradual central vision loss**, metamorphopsia, and drusen or neovascularization on exam, not **bull's eye maculopathy**. - Although the patient's age is a risk factor, the specific finding of **bull's eye macular lesions** points away from this diagnosis. *Diabetic retinopathy* - This condition is characterized by **microaneurysms**, hemorrhages, cotton wool spots, and neovascularization on funduscopic exam. - While the patient has diabetes, the characteristic **bull's eye maculopathy** is not a feature of diabetic retinopathy, nor do her visual symptoms specifically align with its common presentations. *Methanol toxicity* - Methanol poisoning causes **severe visual loss** (often total blindness), **anion gap metabolic acidosis**, and symptoms like abdominal pain and altered mental status. - While the patient consumes moonshine (which can contain methanol), her specific ocular findings and chronic presentation are inconsistent with acute methanol poisoning.

Question 27: A 74-year-old woman presents to the emergency department for shortness of breath and bilateral lower extremity pitting edema. She has had exacerbations like this in the past and notes that she has not been taking her home heart medications as scheduled. Review of systems is negative for any other symptoms including GI, urinary, and musculoskeletal symptoms. Physical exam reveals bilateral pulmonary crackles, lower extremity pitting edema that extends to the hip, and no abdominal tenderness. Neurological exam is unremarkable and the patient is at her baseline mental status. She is subsequently started on BiPAP, given furosemide, and admitted to the hospital. Routine admission workup includes urinalysis, which shows >100,000 cfu/mL of E. coli. She has no known drug allergies. Which of the following is the most appropriate treatment for this patient for this finding?

A. Nitrofurantoin
B. No treatment (Correct Answer)
C. Ceftriaxone
D. Levofloxacin
E. Trimethoprim-sulfamethoxazole

Explanation: ***No treatment*** - This patient presents with **asymptomatic bacteriuria (ASB)**, characterized by significant bacteriuria without symptoms of a urinary tract infection (UTI). - Treatment of ASB is generally **not recommended** in non-pregnant women, as it does not reduce morbidity or mortality and can contribute to antibiotic resistance. *Nitrofurantoin* - This antibiotic is used for uncomplicated UTIs but is **not indicated** for asymptomatic bacteriuria. - Its use in ASB would expose the patient to potential side effects and contribute to antibiotic resistance without clinical benefit. *Ceftriaxone* - A broad-spectrum antibiotic often used for more severe infections; however, it is **inappropriate** for asymptomatic bacteriuria. - Using parenteral antibiotics like ceftriaxone for ASB significantly increases the risk of **Clostridioides difficile infection** and antimicrobial resistance without improving outcomes. *Levofloxacin* - A fluoroquinolone, typically reserved for complicated UTIs or situations where other antibiotics are not suitable, especially in patients with **drug allergies**. - Its broad spectrum and potential for significant side effects like tendon rupture and **Clostridioides difficile infection** make it an **unsuitable choice** for asymptomatic bacteriuria. *Trimethoprim-sulfamethoxazole* - A common antibiotic for uncomplicated UTIs, but like other antibiotics, it is **not recommended** for asymptomatic bacteriuria. - Treating ASB with this drug could lead to side effects such as **rash** or **hyperkalemia** and promote resistance to this widely used agent.

Question 28: A 15-year-old boy with Down syndrome is admitted to the hospital because of a 2-week history of pallor, easy bruising, and progressive fatigue. He has a history of acute lymphoblastic leukemia that has been in remission for 2 years. Examination shows cervical and axillary lymphadenopathy. Bone marrow biopsy predominantly shows immature cells that stain positive for terminal deoxynucleotidyl transferase. A diagnosis of relapsed acute lymphoblastic leukemia is made. Treatment with a combination chemotherapeutic regimen including teniposide is initiated. The effect of this drug is best explained by which of the following mechanisms of action?

A. Inhibition of microtubule formation
B. Increase in double-stranded DNA breaks (Correct Answer)
C. Inhibition of topoisomerase I
D. Decrease in nucleotide synthesis
E. Inhibition of thymidylate synthase

Explanation: ***Increase in double-stranded DNA breaks*** - **Teniposide** is a **topoisomerase II inhibitor**, which creates **double-stranded DNA breaks** by preventing the relegation of DNA after it has been cleaved. - This leads to an accumulation of DNA breaks, triggering **apoptosis** in rapidly dividing cancer cells. *Inhibition of microtubule formation* - This mechanism is characteristic of **vinca alkaloids** (e.g., vincristine, vinblastine) and **taxanes** (e.g., paclitaxel, docetaxel). - These drugs interfere with the formation and function of **microtubules**, which are essential for cell division and cell structure. *Inhibition of topoisomerase I* - This action is associated with **camptothecins** (e.g., irinotecan, topotecan), which specifically target **topoisomerase I**. - Topoisomerase I inhibitors prevent the unwinding of DNA during replication, leading to **single-strand DNA breaks**. *Decrease in nucleotide synthesis* - This mechanism is employed by **antimetabolites** like **methotrexate** (folate antagonist) and **purine/pyrimidine analogs**. - These drugs interfere with the production of DNA and RNA building blocks, thus inhibiting cell growth and division. *Inhibition of thymidylate synthase* - This is the primary mechanism of action for **5-fluorouracil (5-FU)**, which is a pyrimidine analog. - By inhibiting **thymidylate synthase**, 5-FU prevents the synthesis of **thymidine monophosphate (dTMP)**, a crucial component for DNA synthesis.

Question 29: A 62-year-old male presents to his primary care physician complaining of a chronic cough. He reports a six-month history of progressively worsening cough and occasional hemoptysis. He has lost ten pounds over the same time frame. His medical history is notable for hypertension, hyperlipidemia, and diabetes mellitus. He has a 50-pack-year smoking history. A chest radiograph reveals a coin-like central cavitary lesion. Tissue biopsy demonstrates findings consistent with squamous cell carcinoma. The patient is referred to a pulmonologist who starts the patient on a chemotherapeutic drug. However, after several weeks on the drug, the patient develops sensorineural hearing loss. Which of the following mechanisms of action is consistent with the most likely medication prescribed in this case?

A. Folate analog
B. Microtubule inhibitor
C. Platinum-based DNA crosslinker (Correct Answer)
D. DNA alkylating agent
E. DNA intercalating agent

Explanation: ***Platinum-based DNA crosslinker*** - The patient's presentation with a **central cavitary lesion** and **squamous cell carcinoma** of the lung, along with a significant smoking history, strongly suggests a **chemotherapeutic regimen** that commonly includes platinum-based drugs like **cisplatin** or **carboplatin**. - **Sensorineural hearing loss** (**ototoxicity**) is a well-known and significant side effect of platinum-based antineoplastic agents, which create **DNA crosslinks** to inhibit replication and transcription. *Folate analog* - **Folate analogs** like **methotrexate** inhibit **dihydrofolate reductase**, interfering with DNA synthesis, and are used in various cancers. - While they can cause myelosuppression and mucositis, **ototoxicity** is **not a characteristic side effect** of this class of drugs. *Microtubule inhibitor* - **Microtubule inhibitors** (**e.g., taxanes, vinca alkaloids**) interfere with microtubule function, essential for cell division. - They are associated with **neuropathy** and myelosuppression, but **sensorineural hearing loss** is **not a prominent adverse effect**. *DNA alkylating agent* - **DNA alkylating agents** form covalent bonds with DNA, leading to DNA damage and cell death. - While they cause a range of toxicities, **significant ototoxicity** leading to sensorineural hearing loss is **not typically a hallmark** of this group compared to platinum-based drugs. *DNA intercalating agent* - **DNA intercalating agents** insert themselves between DNA base pairs, unwinding the helix and inhibiting replication and transcription. - Drugs like **doxorubicin** (an anthracycline) can cause cardiotoxicity and myelosuppression, but **ototoxicity** is **not a primary adverse effect**.

Question 30: A 64-year-old man presents to his primary care physician for a fall. The patient states that he has felt abnormally clumsy lately and has noticed himself tripping and bumping into things. He states he otherwise is healthy but admits to having unprotected sex with multiple people recently. His temperature is 99.5°F (37.5°C), blood pressure is 127/68 mm Hg, pulse is 100/min, respiratory rate is 24/min, and oxygen saturation is 98% on room air. Laboratory values are ordered as seen below. Hemoglobin: 9 g/dL Hematocrit: 30% Mean corpuscular volume: 110 fL Leukocyte count: 6,500/mm^3 with normal differential Platelet count: 197,000/mm^3 AST: 15 U/L ALT: 22 U/L GGT: 10 U/L Physical exam is notable for a broad-based and unstable gait. Which of the following conditions is the most likely etiology of this patient's presentation?

A. Tertiary syphilis
B. Vegetarian diet
C. Colon cancer
D. Chronic alcoholism
E. Chronic gastritis (Correct Answer)

Explanation: ***Chronic gastritis*** - Chronic gastritis can lead to **vitamin B12 deficiency** due to impaired **intrinsic factor** production, resulting in **macrocytic anemia** (evidenced by **Hb 9 g/dL**, **MCV 110 fL**). - Vitamin B12 deficiency can cause neurological symptoms like **ataxia** and **clumsiness (broad-based, unstable gait)** from **subacute combined degeneration** of the spinal cord. *Tertiary syphilis* - Tertiary syphilis can cause **tabes dorsalis**, characterized by ataxia and sensory deficits, which could explain the gait disturbance. - However, the lab findings of **macrocytic anemia** (high MCV) are more indicative of **vitamin B12 deficiency**, which is not a direct consequence of syphilis. *Vegetarian diet* - A strict vegetarian diet can lead to **vitamin B12 deficiency** because B12 is primarily found in animal products. - While it can cause macrocytic anemia and neurological symptoms, the patient's history of **unprotected sex** and lack of dietary information makes other etiologies more likely. *Colon cancer* - Colon cancer typically causes **microcytic anemia** due to chronic blood loss, not **macrocytic anemia**. - While it can cause fatigue, it does not directly explain the neurological symptoms of clumsiness and unstable gait in this manner. *Chronic alcoholism* - Chronic alcoholism can lead to **macrocytic anemia** due to **folate deficiency** or direct toxic effects on the bone marrow. - While it can cause neurological deficits (e.g., Wernicke-Korsakoff syndrome, alcoholic polyneuropathy), the provided liver enzymes (AST 15 U/L, ALT 22 U/L, GGT 10 U/L) are **normal**, making severe chronic alcoholism less likely to be the primary cause of his symptoms and lab findings.

Question 31: A 45-year-old woman with a history of alcoholic hepatitis returns to clinic for follow-up after being diagnosed with rheumatoid arthritis and started on NSAIDs. She complains of continued joint effusions and increasing morning stiffness. Given this patient's presentation and history, which of the following drugs presents the greatest risk when started for the management of her condition?

A. Etanercept
B. Corticosteroids
C. Cyclosporine
D. Hydroxychloroquine
E. Methotrexate (Correct Answer)

Explanation: ***Methotrexate*** - **Methotrexate** is a cornerstone of rheumatoid arthritis treatment but is **hepatotoxic** and contraindicated in patients with significant liver disease, like this patient with a history of **alcoholic hepatitis**. - Its use in this patient would significantly **exacerbate liver damage** and could lead to severe hepatic complications. *Etanercept* - **Etanercept** is a TNF-alpha inhibitor and generally well-tolerated, but carries risks of **infections** and **demyelinating disorders**, not primarily liver toxicity. - While it can sometimes impact liver enzymes, it is not a direct contraindication in stable, non-active liver disease. *Corticosteroids* - **Corticosteroids** can cause side effects such as **osteoporosis**, **hyperglycemia**, and **infections**, but they are often used cautiously for short-term control in patients with liver disease. - They are not primarily hepatotoxic to the extent of methotrexate. *Cyclosporine* - **Cyclosporine** is an immunosuppressant that can be **nephrotoxic** and may cause **hypertension** or **gingival hyperplasia**. - While it has some potential for hepatotoxicity, it is generally considered less risky than methotrexate in patients with a history of alcoholic liver disease. *Hydroxychloroquine* - **Hydroxychloroquine** is a relatively safe DMARD, with primary side effects including **retinal toxicity** and **gastrointestinal upset**. - It has a low risk of significant hepatotoxicity and is generally considered safe in patients with liver disease.

Question 32: A mother brings her 8-month-old child to your pediatric clinic with concerns of a rash. Physical exam reveals an erythematous, weeping rash involving bilateral cheeks and scalp. You prescribe a topical agent that is considered the first-line pharmacological treatment for this condition. What is a common concern that the mother should be alerted to regarding long-term use of this topical agent?

A. Paresthesia
B. Hypoglycemia
C. Hyperpigmentation
D. Increased risk of melanoma
E. Skin atrophy (Correct Answer)

Explanation: ***Skin atrophy*** - The rash described (erythematous, weeping, involving cheeks and scalp in an 8-month-old) is characteristic of **atopic dermatitis** (eczema). First-line pharmacological treatment for atopic dermatitis involves **topical corticosteroids**. - **Long-term use of topical corticosteroids**, especially on delicate skin like that of an infant's face, can lead to **skin atrophy**, characterized by thinning of the skin, telangiectasias, and striae. *Paresthesia* - This symptom, often described as tingling or numbness, is not a typical side effect associated with the **long-term use of topical corticosteroids**. - Paresthesia is more commonly linked to nerve damage, vitamin deficiencies, or certain systemic medications. *Hypoglycemia* - **Systemic corticosteroids** can cause hyperglycemia, but topical corticosteroids generally have minimal systemic absorption unless very potent, applied over large areas, or under occlusion. - **Topical corticosteroids** are not associated with hypoglycemia. *Hyperpigmentation* - While skin changes can occur with chronic inflammation, topical corticosteroids are generally associated with **hypopigmentation** (lightening of the skin) rather than hyperpigmentation, particularly with prolonged use or on darker skin types. - **Post-inflammatory hyperpigmentation** can occur after eczema resolves, but it's not a direct side effect of the topical steroid itself. *Increased risk of melanoma* - There is **no established link** between the long-term use of topical corticosteroids and an increased risk of developing melanoma. - Melanoma is a type of skin cancer primarily associated with UV radiation exposure and genetic factors.

Question 33: A 33-year-old woman comes to the physician because of constipation, abdominal pain, and decreased appetite for the past 2 months. She started a new diet and has been exercising 2 hours daily for several months in order to lose weight. She has a history of hypertension and hypothyroidism. She does not smoke or drink alcohol. Current medications include hydrochlorothiazide, a multivitamin, and levothyroxine. She recently started taking over-the-counter supplements with each meal. Her temperature is 36.2°C (97.2°F), pulse is 92/min, and blood pressure is 102/78 mm Hg. Examination shows dry mucous membranes. Cardiopulmonary examination shows no abnormalities. Her abdomen is soft; bowel sounds are decreased. Serum studies show: Calcium 12.8 mg/dL Phosphorus 4.6 mg/dL Bicarbonate 22 mEq/L Albumin 4 g/dL PTH 180 pg/mL TSH 9 μU/mL Free T4 5 μg/dL Which of the following is the most likely underlying cause of this patient's symptoms?

A. Primary hypothyroidism
B. Excess calcium carbonate intake
C. Primary hyperparathyroidism
D. Vitamin D toxicity (Correct Answer)
E. Vitamin A toxicity

Explanation: ***Vitamin D toxicity*** - The patient's **elevated calcium** (12.8 mg/dL) and **normal to mildly elevated phosphorus** (4.6 mg/dL) suggest hypercalcemia with increased intestinal absorption. - The patient's recent intake of "over-the-counter supplements with each meal" suggests potential excessive vitamin D intake, especially given her focus on weight loss and exercise, which may have prompted supplementation. - **Note:** The PTH value of 180 pg/mL is elevated rather than suppressed, which would be atypical for vitamin D toxicity. In classic vitamin D toxicity, PTH should be suppressed (<20 pg/mL) due to negative feedback from hypercalcemia. This PTH elevation may represent concurrent primary hyperparathyroidism or a laboratory reporting issue. *Primary hypothyroidism* - While the patient has elevated TSH (9 μU/mL), hypothyroidism typically causes **hypocalcemia** or normocalcemia, not hypercalcemia. - The hypercalcemia with the patient's supplement use points to a different etiology. *Excess calcium carbonate intake* - Excess calcium carbonate intake could cause hypercalcemia but typically leads to **low phosphorus** due to calcium-phosphate binding in the gut and renal excretion. - **Milk-alkali syndrome** (from excess calcium carbonate) presents with hypercalcemia, metabolic alkalosis, and renal insufficiency. The patient's normal bicarbonate (22 mEq/L) makes this less likely. *Primary hyperparathyroidism* - **Primary hyperparathyroidism** presents with **hypercalcemia** and **elevated PTH**, but classically causes **hypophosphatemia** due to PTH's phosphaturic effect. - This patient has normal to mildly elevated phosphorus (4.6 mg/dL), which is atypical for primary hyperparathyroidism where phosphorus is usually low (<2.5 mg/dL). - The history of new supplement use makes an exogenous cause (vitamin D toxicity) more likely than a parathyroid adenoma. *Vitamin A toxicity* - **Vitamin A toxicity** can cause hypercalcemia but typically presents with distinctive features including **dry skin**, **cheilosis**, **alopecia**, **hepatomegaly**, and **pseudotumor cerebri** (increased intracranial pressure). - These characteristic findings are not present in this patient, making vitamin A toxicity less likely than vitamin D toxicity given the supplement history.

Question 34: A 58-year-old female presents with a two-month history of intermittent non-bloody diarrhea. She reports that she has been following a raw food diet for six months to help her lose weight. The patient’s medical history is significant for anxiety, treated with fluvoxamine, and osteopenia. She reports her mother has lactose intolerance and has recently been diagnosed with osteoporosis. The patient denies any tobacco or alcohol use. When asked about recent travel, she reports she returned three months ago from a mission trip in Uganda. The patient’s temperature is 99°F (37.2°C), blood pressure is 130/78 mmHg, pulse is 70/min, and respirations are 14/min with an oxygen saturation of 98% O2 on room air. On physical exam, a new-onset systolic ejection murmur is noted and is heard loudest at the left second intercostal space. Which of the following may develop in this patient?

A. Decreased levels of chromogranin A
B. Vitamin D deficiency
C. Positive hydrogen breath test
D. Low platelet count
E. Niacin deficiency (Correct Answer)

Explanation: ***Niacin deficiency*** - This patient most likely has **carcinoid syndrome** from a carcinoid tumor (possibly acquired during travel to Uganda or from chronic gastrointestinal pathology). - The classic triad includes: **diarrhea**, **flushing**, and **right-sided heart valve disease** (explaining the new systolic ejection murmur at the left 2nd intercostal space - pulmonary valve area). - Carcinoid tumors produce excessive **serotonin** by diverting **tryptophan** metabolism away from **niacin (vitamin B3) synthesis**. - This leads to **pellagra** (niacin deficiency) with the "3 D's": **diarrhea, dermatitis, and dementia**. - The raw food diet and chronic diarrhea may contribute to malabsorption, further increasing deficiency risk. *Decreased levels of chromogranin A* - **Chromogranin A** is a biomarker for neuroendocrine tumors and would be **elevated** (not decreased) in carcinoid syndrome. - This option represents the opposite of what would occur in this patient with suspected carcinoid syndrome. *Vitamin D deficiency* - While the patient has **osteopenia** and risk factors for vitamin D deficiency, this does not explain the constellation of **diarrhea plus cardiac murmur**. - Vitamin D deficiency primarily affects bone health and does not cause the valvular heart disease seen in this patient. *Positive hydrogen breath test* - A positive hydrogen breath test indicates **lactose intolerance** or **small intestinal bacterial overgrowth (SIBO)**. - While the patient's mother has lactose intolerance, this would not explain the **new cardiac murmur** or the full clinical picture of carcinoid syndrome. *Low platelet count* - **Thrombocytopenia** is not a characteristic feature of carcinoid syndrome. - The patient's symptoms and physical findings do not suggest a primary hematologic disorder.

Question 35: A 25-year-old woman first presented to your clinic due to morning stiffness, symmetrical arthralgia in her wrist joints, and fatigue. She had a blood pressure of 132/74 mm Hg and heart rate of 84/min. Physical examination revealed tenderness to palpation of both wrists but full range of motion. Anti-citrullinated protein antibodies were positive and ESR was above normal ranges. She was started on methotrexate therapy. She returns for follow up 2 months later and is found to have megaloblastic anemia. What is the mechanism of action of methotrexate?

A. Inhibits vitamin B12 activation
B. Intercalates into strands of DNA
C. Elevates methylmalonic acid levels
D. Elevates tetrahydrofolate levels
E. Inhibits dihydrofolate reductase (Correct Answer)

Explanation: ***Inhibits dihydrofolate reductase*** - **Methotrexate** is a **folate analog** that competitively inhibits **dihydrofolate reductase (DHFR)**, an enzyme essential for converting dihydrofolate to tetrahydrofolate. - This inhibition blocks the synthesis of purines and pyrimidines, crucial for DNA synthesis and cellular proliferation, thereby suppressing immune cell activity in conditions like rheumatoid arthritis. *Inhibits vitamin B12 activation* - **Methotrexate** does not directly inhibit **vitamin B12 activation**; its primary mechanism is antagonism of folate metabolism. - While vitamin B12 is crucial for DNA synthesis, its activation pathway is distinct from the dihydrofolate reductase pathway. *Intercalates into strands of DNA* - **Methotrexate** does not **intercalate into DNA strands**; this mechanism is characteristic of certain **chemotherapeutic agents** that insert themselves between base pairs, causing DNA damage and inhibiting replication. - Methotrexate's action is upstream, targeting folate metabolism required for DNA precursor synthesis. *Elevates methylmalonic acid levels* - **Elevated methylmalonic acid** levels are a hallmark of **vitamin B12 deficiency**, as vitamin B12 is a cofactor for methylmalonyl-CoA mutase. - Methotrexate's mechanism is related to **folate pathway inhibition**, and while it can lead to megaloblastic anemia, it does not directly elevate methylmalonic acid. *Elevates tetrahydrofolate levels* - **Methotrexate** *inhibits* the conversion of dihydrofolate to **tetrahydrofolate**, thus *decreasing* rather than elevating tetrahydrofolate levels. - Lowering **tetrahydrofolate** levels is precisely how methotrexate exerts its therapeutic and adverse effects by impairing nucleotide synthesis.

Question 36: A 2-year-old boy is brought in by his parents to his pediatrician. The boy was born by spontaneous vaginal delivery at 39 weeks and 5 days after a normal pregnancy. The boy has received all age-appropriate vaccinations as of his last visit at 18 months of age. Of note, the boy has confirmed sickle cell disease and the only medication he takes is penicillin prophylaxis. The parents state that they plan on enrolling their son in a daycare, which requires documentation of up-to-date vaccinations. The pediatrician states that their son needs an additional vaccination at this visit, which is a polysaccharide vaccine that is not conjugated to protein. Which of the following matches this description?

A. Pneumovax (Correct Answer)
B. Menactra
C. Prevnar
D. Hib vaccine
E. Live attenuated influenza vaccine

Explanation: ***Pneumovax*** - **Pneumovax** (PCV23, PPSV23) is a **polysaccharide vaccine** that is not conjugated to a protein carrier. Children with **sickle cell disease** should receive this vaccine due to their immunocompromised state and increased risk of encapsulated bacterial infections. - The Centers for Disease Control and Prevention (CDC) recommends PPSV23 for children aged 2 years and older with chronic medical conditions such as **sickle cell disease**, usually administered 8 weeks after their last PCV13 dose. *Menactra* - **Menactra** is a **quadrivalent meningococcal conjugate vaccine** (MCV4), meaning it contains a polysaccharide antigen conjugated to a protein carrier. - This vaccine primarily targets *Neisseria meningitidis* and is different from the pneumococcal vaccine required here. *Prevnar* - **Prevnar** (PCV13) is a **pneumococcal conjugate vaccine**, meaning its polysaccharide antigens are conjugated to a protein carrier. - While important for children with sickle cell disease, the question specifically asks for a vaccination that is a **polysaccharide vaccine that is not conjugated to protein**. *Hib vaccine* - The **Hib vaccine** (against *Haemophilus influenzae* type b) is a **conjugate vaccine**, meaning its polysaccharide capsule is linked to a protein carrier to enhance immunogenicity, particularly in infants. - This vaccine is typically given earlier in childhood and is not the "additional" unconjugated polysaccharide vaccine described. *Live attenuated influenza vaccine* - The **live attenuated influenza vaccine (LAIV)** is a live virus vaccine, not a polysaccharide vaccine. - It is also contraindicated in individuals with certain immunocompromising conditions, such as some patients with sickle cell disease.

Question 37: A 57-year-old man presents to the emergency department with fatigue. He states that his symptoms started yesterday and have been worsening steadily. The patient endorses a recent weight loss of 7 pounds this past week and states that he feels diffusely itchy. The patient has a past medical history of alcohol abuse, obesity, asthma, and IV drug use. His current medications include metformin, atorvastatin, albuterol, and fluticasone. In addition, the patient admits to smoking and drinking more than usual lately due to the stress he has experienced. His temperature is 98.7°F (37.1°C), blood pressure is 130/75 mmHg, pulse is 90/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is notable for an ill-appearing man. The patient's skin appears yellow. Abdominal exam is notable for right upper quadrant tenderness. Cardiac and pulmonary exams are within normal limits. Laboratory values are ordered as seen below: Hemoglobin: 14 g/dL Hematocrit: 42% Leukocyte count: 5,500 cells/mm^3 with normal differential Platelet count: 70,000/mm^3 Partial thromboplastin time: 92 seconds Prothrombin time: 42 seconds AST: 1110 U/L ALT: 990 U/L Which of the following is most likely to be found in this patient's history?

A. Recent antibiotic treatment with gentamicin
B. Appropriate acute management of a deep vein thrombosis
C. Decreased UDP-glucuronosyltransferase activity at birth
D. Prosthetic valve with appropriate post-operative care
E. Severe migraine headaches treated with acetaminophen (Correct Answer)

Explanation: ***Severe migraine headaches treated with acetaminophen*** - The patient's presentation with **acute liver failure** (elevated AST/ALT, coagulopathy, jaundice) in the context of increased stress and likely increased medication use, strongly suggests **acetaminophen overdose** as the cause. Given his past medical history of alcohol abuse further increases his risk of liver injury with acetaminophen. - While other etiologies such as acute viral hepatitis or ischemic hepatitis should be considered, acetaminophen overdose is the most common cause of acute liver failure. *Recent antibiotic treatment with gentamicin* - **Gentamicin** is an **aminoglycoside antibiotic** primarily associated with **nephrotoxicity** and **ototoxicity**, not acute liver failure. - Liver dysfunction is not a typical adverse effect of gentamicin, making it an unlikely cause of the patient's symptoms. *Appropriate acute management of a deep vein thrombosis* - Treatment for deep vein thrombosis typically involves **anticoagulants** such as heparin or warfarin. While these medications can rarely cause liver injury, the severe and acute elevation in liver enzymes and coagulopathy seen here points away from a standard anticoagulant side effect. - The clinical picture aligns much more closely with a direct hepatotoxic injury rather than an idiosyncratic reaction to anticoagulation. *Decreased UDP-glucuronosyltransferase activity at birth* - **Decreased UDP-glucuronosyltransferase (UGT) activity** at birth is characteristic of **Crigler-Najjar syndrome** or **Gilbert's syndrome**, which cause **unconjugated hyperbilirubinemia**. - These are typically chronic conditions that present earlier in life and do not cause acute, severe hepatocellular injury with massively elevated AST/ALT and coagulopathy. *Prosthetic valve with appropriate post-operative care* - A prosthetic heart valve, even with appropriate post-operative care, is not directly linked to acute liver failure. - While complications like endocarditis or hemolysis could cause some liver involvement, they would not typically present with this constellation of severe acute symptoms and laboratory findings.

Question 38: A 63-year-old man with inoperable esophageal carcinoma undergoes palliative chemoradiotherapy. Four hours after his first infusion of carboplatin and paclitaxel, he develops nausea and 3 episodes of vomiting and dry heaving. This adverse reaction is caused by stimulation of a brain region on the floor of the fourth ventricle. Chemotherapeutic drugs are able to stimulate this region because of the absence of a cell junction that is composed of which of the following proteins?

A. Claudins and occludins (Correct Answer)
B. Integrins
C. Cadherins and catenins
D. Connexins
E. Desmogleins and desmocollins

Explanation: ***Claudins and occludins*** - The **area postrema**, located on the floor of the fourth ventricle, is a **chemoreceptor trigger zone (CTZ)** that detects toxins in the blood. - This region lacks a fully functional **blood-brain barrier** due to the absence of tight junctions, which are primarily composed of **claudins and occludins**, allowing chemotherapeutic agents to stimulate it and induce nausea and vomiting. *Integrins* - **Integrins** are primarily involved in **cell-matrix adhesion**, connecting the cell cytoskeleton to the extracellular matrix. - They are not the primary components of **tight junctions** that form the blood-brain barrier. *Cadherins and catenins* - **Cadherins** are crucial for **cell-cell adhesion** in adherens junctions and desmosomes, and they link to the actin cytoskeleton via **catenins**. - While important for cell adhesion, they are not the main proteins forming the **occluding seal** of tight junctions. *Connexins* - **Connexins** are the structural proteins that form **gap junctions**, which allow for direct communication and passage of small molecules between adjacent cells. - They are not involved in forming the **impermeable barrier** characteristic of tight junctions. *Desmogleins and desmocollins* - **Desmogleins** and **desmocollins** are specific types of cadherins found in **desmosomes**, which provide strong cell-cell adhesion and resistance to mechanical stress. - Desmosomes are different from **tight junctions**, which prevent paracellular diffusion.

Question 39: A 47-year-old woman presents to the physician with complaints of fatigue accompanied by symmetric pain, swelling, and stiffness in her wrists, fingers, knees, and other joints. She describes the stiffness as being particularly severe upon awakening, but gradually improves as she moves throughout her day. Her physician initially suggests that she take NSAIDs. However, after a few months of minimal symptomatic improvement, she is prescribed an immunosuppressive drug that has a mechanism of preventing IL-2 transcription. What is the main toxicity that the patient must be aware of with this particular class of drugs?

A. Pancytopenia
B. Osteoporosis
C. Hepatotoxicity
D. Nephrotoxicity (Correct Answer)
E. Hyperglycemia

Explanation: ***Nephrotoxicity*** - The drug described, which prevents **IL-2 transcription**, is likely a **calcineurin inhibitor** like cyclosporine or tacrolimus, often used in autoimmune diseases. - **Nephrotoxicity** (kidney damage) is a major dose-limiting toxicity of calcineurin inhibitors, causing both acute and chronic kidney injury. *Pancytopenia* - While some immunosuppressants can cause **pancytopenia** (e.g., azathioprine, methotrexate), it is not the classic or primary toxicity associated with calcineurin inhibitors. - Calcineurin inhibitors primarily affect **renal function** and can cause other side effects like hypertension or neurotoxicity. *Osteoporosis* - **Osteoporosis** is a known side effect of long-term glucocorticoid use, but not typically a primary toxicity of calcineurin inhibitors. - Glucocorticoids reduce bone formation and increase bone resorption, leading to bone density loss. *Hepatotoxicity* - **Hepatotoxicity** (liver damage) can occur with various immunosuppressants, such as methotrexate, but it is not the most prominent or defining toxicity for calcineurin inhibitors. - While cyclosporine can cause some liver enzyme elevation, **nephrotoxicity** is far more common and severe. *Hyperglycemia* - **Hyperglycemia** can be a side effect of some immunosuppressants, particularly **glucocorticoids** and **tacrolimus** (another calcineurin inhibitor). - However, for the class of drugs that prevent IL-2 transcription (calcineurin inhibitors), **nephrotoxicity** remains the most significant and common major toxicity to be aware of.

Question 40: A 33-year-old woman with a history of multiple sclerosis is brought to the physician because of dizziness, urinary incontinence, loss of vision in her right eye, and numbness and weakness of the left leg. She has had recurrent episodes of neurological symptoms despite several changes in her medication regimen. An MRI of the brain shows several new enhancing lesions in the periventricular white matter and the brainstem. Treatment with a drug that binds to CD52 is initiated. Which of the following agents was most likely prescribed?

A. Alemtuzumab (Correct Answer)
B. Eculizumab
C. Abciximab
D. Rituximab
E. Bevacizumab

Explanation: ***Alemtuzumab*** - **Alemtuzumab** is a monoclonal antibody that targets **CD52**, a glycoprotein found on the surface of mature lymphocytes (T and B cells), monocytes, and macrophages, leading to their depletion. - It is used in **highly active relapsing-remitting multiple sclerosis (RRMS)**, especially when other disease-modifying therapies have failed, which aligns with the patient's history of recurrent neurological symptoms and new enhancing lesions. *Eculizumab* - **Eculizumab** targets the **C5 complement protein** and is used for conditions like **paroxysmal nocturnal hemoglobinuria** and **atypical hemolytic uremic syndrome**, not multiple sclerosis. - It works by inhibiting the complement cascade, which is not the primary mechanism of action for MS treatment involving lymphocyte depletion. *Abciximab* - **Abciximab** is a **glycoprotein IIb/IIIa inhibitor** that prevents platelet aggregation and is used as an antiplatelet agent in acute coronary syndromes and percutaneous coronary intervention. - Its mechanism of action and primary indication are unrelated to the immunological processes involved in multiple sclerosis. *Rituximab* - **Rituximab** targets **CD20** on B cells and is used in conditions like **non-Hodgkin lymphoma**, **chronic lymphocytic leukemia**, and certain autoimmune diseases like **rheumatoid arthritis** and **vasculitis**. - While it's a B-cell depleting agent and has shown efficacy in MS, the question specifically asks for a drug that binds to **CD52**, not CD20. *Bevacizumab* - **Bevacizumab** is an anti-VEGF antibody that inhibits **angiogenesis** and is primarily used in the treatment of various cancers, such as colorectal, lung, and renal cell carcinoma. - Its mechanism of action involving inhibition of vascular endothelial growth factor (VEGF) is not indicated for the management of multiple sclerosis.

Question 41: A 65-year-old male presents to the physician after noticing gross blood with urination. He reports that this is not associated with pain. The patient smokes 1.5 packs per day for 45 years. Dipstick analysis is positive for blood, with 5 RBC per high-power field (HPF) on urinalysis. A cystoscopy is performed, which is significant for a lesion suspicious for malignancy. A biopsy was obtained, which is suggestive of muscle-invasive transitional cell carcinoma. Before radical cystectomy is performed, the patient is started on cisplatin-based chemotherapy. Which of the following is most likely associated with this chemotherapeutic drug?

A. Cardiotoxicity
B. Hemorrhagic cystitis
C. Addition of mesna decreases drug toxicity
D. Gentamicin enhances toxicity risk (Correct Answer)
E. Myelosuppression

Explanation: ***Gentamicin enhances toxicity risk*** - **Cisplatin** is a platinum-based chemotherapeutic agent with characteristic toxicities including **nephrotoxicity** (dose-limiting), **ototoxicity**, and **peripheral neuropathy**. - **Gentamicin** is an aminoglycoside antibiotic that is also **nephrotoxic** and **ototoxic**. - Concurrent use of gentamicin with cisplatin significantly **enhances the risk of both nephrotoxicity and ototoxicity** due to additive effects on renal tubular cells and cochlear hair cells. - This is a **clinically important drug-drug interaction** that must be avoided or carefully monitored. *Myelosuppression* - While cisplatin can cause mild myelosuppression, this is **not its most characteristic or dose-limiting toxicity**. - **Carboplatin** (another platinum agent) is much more associated with myelosuppression than cisplatin. - Cisplatin's hallmark toxicities are **nephrotoxicity, ototoxicity, and neurotoxicity**. *Cardiotoxicity* - **Cardiotoxicity** is primarily associated with **anthracyclines** (e.g., doxorubicin, daunorubicin), not cisplatin. - Anthracyclines cause dilated cardiomyopathy through free radical damage. *Hemorrhagic cystitis* - **Hemorrhagic cystitis** is a well-known side effect of **cyclophosphamide** and **ifosfamide**, not cisplatin. - This condition is caused by the metabolite **acrolein**, which irritates the bladder lining. *Addition of mesna decreases drug toxicity* - **Mesna** (2-mercaptoethane sulfonate sodium) is specifically used to prevent hemorrhagic cystitis caused by **cyclophosphamide** and **ifosfamide** by binding and detoxifying acrolein. - Mesna does **not mitigate cisplatin toxicity**; cisplatin toxicity is managed with **adequate hydration and saline diuresis** to protect the kidneys.

Question 42: A 32-year-old woman comes to the physician with fever and malaise. For the past 2 days, she has felt fatigued and weak and has had chills. Last night, she had a temperature of 40.8°C (104.2°F). She has had a sore throat since this morning. The patient was recently diagnosed with Graves disease and started on methimazole. Laboratory studies show: Hemoglobin 13.3 g/dL Leukocyte count 3,200/mm3 Segmented neutrophils 8% Basophils < 1% Eosinophils < 1% Lymphocytes 80% Monocytes 11% Platelet count 220,000/mm3 Which of the following is the most appropriate next step in management?

A. Discontinue methimazole (Correct Answer)
B. Switch to propylthiouracil
C. Bone marrow biopsy
D. Test for EBV, HIV, and CMV
E. Begin oral aminopenicillin

Explanation: ***Correct: Discontinue methimazole*** - This patient's symptoms (fever, sore throat, malaise) along with severe **neutropenia** (8% of 3,200/mm³ = 256/mm³) after starting methimazole indicate **drug-induced agranulocytosis** - Agranulocytosis is a rare but serious side effect of thionamides that requires **immediate cessation** of the causative drug to prevent life-threatening infections - This is the most urgent priority in management *Incorrect: Switch to propylthiouracil* - Propylthiouracil (PTU) is another thionamide that can also cause agranulocytosis - There is risk of **cross-reactivity** between thionamides - Switching to another thionamide is inappropriate in a patient with clear drug-induced agranulocytosis *Incorrect: Bone marrow biopsy* - While bone marrow biopsy would confirm lack of granulocyte precursors, it is not the most immediate next step - The clinical picture and peripheral blood counts are already sufficiently diagnostic - The urgent priority is **discontinuation of the offending drug**, not further diagnostic testing *Incorrect: Test for EBV, HIV, and CMV* - While viral infections can cause leukopenia, the specific context of recent methimazole initiation and profound neutropenia strongly suggests **drug-induced agranulocytosis** - Testing for viruses is less urgent than addressing the suspected drug reaction - This would be considered if drug-induced cause is ruled out *Incorrect: Begin oral aminopenicillin* - While the patient is at high risk of serious bacterial infection given severe neutropenia and fever, the **most appropriate initial step** is removing the causative agent - Antibiotic therapy should be initiated promptly *after* drug discontinuation - Treatment would typically involve **intravenous broad-spectrum antibiotics** in the hospital setting, not oral aminopenicillin

Question 43: A 17-year-old girl is brought into the physician's office with complaints of nausea, vomiting, headache, and blurry vision. In preparation for final exams the patient's mother started her on an array of supplements and herbal preparations given the "viral illness" that is prevalent at her school. Despite these remedies, the girl has been feeling perpetually worse, and yesterday during cheerleading practice had to sit out after vomiting and feeling dizzy. The patient admits to falling during one of the exercises and hitting her head on another girl's shin due to her dizziness. When asked to clarify her dizziness, the patient states that she feels rather lightheaded at times. The patient's BMI is 19 kg/m^2. She endorses diarrhea of recent onset, and some non-specific, diffuse pruritus of her skin which she attributes to stress from her finals. The patient has a past medical history of anxiety, depression, and excessive exercise habits. On physical exam the patient is alert and oriented to place, person, and time, and answers questions appropriately. She denies any decreased ability to participate in school or to focus. Her skin is dry and peeling with a minor yellow discoloration. Her memory is intact at 1 minute and 5 minutes for 3 objects. The patient's pupils are equal and reactive to light and there are no abnormalities upon examination of cranial nerve III, IV or VI. Which of the following is the most likely cause of this patient's symptoms?

A. Idiopathic intracranial hypertension
B. Migraine headache with aura
C. Bulimia nervosa
D. Head trauma
E. Supplement use (Correct Answer)

Explanation: ***Supplement use*** - The patient's history of being started on "an array of supplements and herbal preparations" for a "viral illness," combined with **nausea, vomiting, headache, blurry vision, dizziness, diarrhea, and pruritus,** strongly suggests an adverse reaction or toxicity from these supplements. - The **dry, peeling skin with minor yellow discoloration** could indicate vitamin A toxicity, as many "viral illness" supplements contain high doses of vitamin A, and this symptom set is highly consistent with hypervitaminosis A. *Idiopathic intracranial hypertension* - While idiopathic intracranial hypertension (IIH) can present with **headache, nausea, vomiting, and blurry vision**, it typically involves **papilledema** on fundoscopic exam, which is not mentioned and generally causes more severe visual disturbances than described. - IIH is more common in **obese young women**, and this patient has a BMI of 19 kg/m^2, making it less likely. *Migraine headache with aura* - Migraines can cause **headache, nausea, vomiting, and aura** (e.g., blurry vision, dizziness), but the **diarrhea, pruritus, diffuse dry skin with yellow discoloration**, and the onset coinciding with supplement use are not typical features of a migraine. - The symptoms are described as progressively worsening over time, which is less consistent with a typical migraine attack. *Bulimia nervosa* - The patient has a history of anxiety, depression, and excessive exercise, which can be associated with bulimia, but there is no mention of **binge-eating** or **purging behaviors** (like self-induced vomiting). - The combination of **dry skin, yellow discoloration, diarrhea, and widespread pruritus** is not classic for bulimia nervosa, which often presents with **dental erosions, parotid gland enlargement, and electrolyte imbalances**. *Head trauma* - While the patient admits to falling and hitting her head, her symptoms of **nausea, vomiting, headache, blurry vision, and dizziness** predated the fall and worsened irrespective of it. - She is **alert, oriented, answers questions appropriately, and has intact memory** with no focal neurological deficits or abnormal cranial nerve findings (III, IV, VI), making a significant head injury less likely to be the primary cause of her widespread symptoms.

Question 44: A 50-year-old male with HIV presents to his primary care provider complaining of persistent fevers and night sweats over the past four months. He has also experienced a productive cough. He has been poorly adherent to his HAART regimen. His past medical history also includes gout, hypertension, and diabetes mellitus. He takes allopurinol, enalapril, and metformin. His temperature is 100.9°F (38.3°C), blood pressure is 125/75 mmHg, pulse is 95/min, and respirations are 20/min. His CD4 count is 85 cell/mm^3 and a PPD is negative. A chest radiograph reveals cavitations in the left upper lobe and left lower lobe. Bronchoalveolar lavage reveals the presence of partially acid-fast gram-positive branching rods. A head CT is negative for any intracranial process. A drug with which of the following mechanisms of action is most appropriate for the management of this patient?

A. RNA synthesis inhibitor
B. 30S ribosomal subunit inhibitor
C. Cell wall synthesis inhibitor
D. 50S ribosomal subunit inhibitor
E. Folate synthesis inhibitor (Correct Answer)

Explanation: ***Folate synthesis inhibitor*** - The patient's presentation with **persistent fevers**, **night sweats**, **productive cough**, **cavitations** on chest radiograph, and a **CD4 count of 85 cells/mm^3** in an HIV-positive individual with poor HAART adherence strongly suggests an **opportunistic infection**. - The bronchoalveolar lavage finding of "**partially acid-fast gram-positive branching rods**" is characteristic of **Nocardia asteroides**. **Trimethoprim-sulfamethoxazole**, which inhibits folate synthesis, is the drug of choice for Nocardia infections. *RNA synthesis inhibitor* - This mechanism is associated with drugs like **rifampin**, which is primarily used for **Mycobacterium tuberculosis** infections. - While tuberculosis can cause cavitations and affect HIV patients, the description of "partially acid-fast gram-positive branching rods" points away from Mycobacterium and towards Nocardia. *30S ribosomal subunit inhibitor* - This mechanism is characteristic of **aminoglycosides** and **tetracyclines**. While some of these drugs might have activity against certain bacteria, they are not first-line for Nocardia. - Aminoglycosides, like amikacin, can be used as an alternative or in combination therapy for severe Nocardia infections, but trimethoprim-sulfamethoxazole is generally preferred. *Cell wall synthesis inhibitor* - This mechanism is typical of **beta-lactam antibiotics** (penicillins, cephalosporins) and **vancomycin**. - Nocardia are **intracellular bacteria** and often express **beta-lactamases**, making standard cell wall inhibitors less effective as monotherapy. *50S ribosomal subunit inhibitor* - This mechanism is characteristic of **macrolides** (e.g., azithromycin, clarithromycin) and **clindamycin**. - While some macrolides might have limited activity against certain Nocardia species, they are not the primary treatment for **Nocardia asteroides** infection.

Question 45: A 3-month-old infant is brought to the emergency department because of lethargy and skin discoloration that started after he was fed some locally prepared baby food from a farmer's market. On presentation, he appears irritable and responds slowly to stimuli. Physical examination reveals rapid, labored breathing and a blue tinge to the infant's skin. A blood sample drawn for testing is found to be darker than normal. Which of the following is the most likely cause of this infant's presentation?

A. Lead
B. Methanol
C. Carbon monoxide
D. Salicylates
E. Nitrates/Nitrites (Correct Answer)

Explanation: ***Nitrates/Nitrites*** - The presentation of **lethargy**, **rapid, labored breathing**, **blue skin tinge (cyanosis)**, and **darker than normal blood** in an infant after consuming food from a farmer's market is highly suggestive of **methemoglobinemia**, commonly caused by nitrate/nitrite poisoning. - Infants are particularly susceptible to nitrates because their immature gastrointestinal tracts have higher pH and a different bacterial flora, leading to increased conversion of nitrates to nitrites, which then oxidize hemoglobin to **methemoglobin**. *Lead* - **Lead poisoning** typically presents with more chronic symptoms such as **abdominal pain**, **constipation**, **developmental delay**, and **anemia**, rather than acute cyanosis and rapid breathing. - It does not cause methemoglobinemia or the characteristic dark blood associated with it. *Methanol* - **Methanol poisoning** usually causes severe metabolic acidosis, visual disturbances (e.g., **blindness**), and neurological symptoms, along with gastrointestinal upset; it does not directly cause cyanosis or dark blood in this manner. - Exposure typically occurs through ingestion of contaminated alcohol or solvents. *Carbon monoxide* - **Carbon monoxide (CO) poisoning** causes a **cherry-red** skin discoloration, not a blue tinge, due to the formation of carboxyhemoglobin, and the blood would appear bright red, not abnormally dark. - Symptoms include headache, nausea, dizziness, and confusion, but not methemoglobinemia. *Salicylates* - **Salicylate poisoning** (e.g., aspirin) leads to a mixed respiratory alkalosis and metabolic acidosis, fever, tinnitus, and hyperventilation; it does not cause cyanosis or the dark blood associated with methemoglobinemia. - While it can cause lethargy and altered mental status, the specific presentation of blue skin and dark blood points away from salicylates.

Question 46: A previously healthy 48-year-old man comes to the physician because of a 2-month history of weight loss and yellowing of the skin. He works as a farmer and cultivates soybean and corn. He does not smoke, drink alcohol, or use illicit drugs. His vital signs are within normal limits. Physical examination shows scleral icterus and tender hepatomegaly. Ultrasonography of the abdomen shows a 5-cm nodular lesion in the right lobe of the liver. Further evaluation of the lesion confirms hepatocellular carcinoma. The activity of which of the following enzymes most likely contributed to the pathogenesis of this patient's condition?

A. Cytochrome P450 monooxygenases (Correct Answer)
B. Nuclear glycosylases
C. Lysosomal serine proteases
D. Cytosolic cysteine proteases
E. Peroxisomal catalases

Explanation: ***Cytochrome P450 monooxygenases*** - This patient, a farmer exposed to agricultural products like soybean and corn, likely developed **hepatocellular carcinoma** due to exposure to **aflatoxins**, which are common contaminants of these crops. - **Aflatoxins** are metabolized by **hepatic cytochrome P450 monooxygenases** into highly reactive **epoxide intermediates**, which can bind to DNA and cause mutations, leading to cancer. *Nuclear glycosylases* - **Nuclear glycosylases** are involved in **DNA repair**, specifically in the base excision repair pathway, removing damaged or incorrect bases from DNA. - While important for maintaining genomic integrity, their activity is not typically implicated in the initial formation of carcinogenic metabolites like those from aflatoxins. *Lysosomal serine proteases* - **Lysosomal serine proteases** are involved in protein degradation within lysosomes and are not directly involved in the metabolic activation of procarcinogens or the initial steps of DNA damage leading to hepatocellular carcinoma. - Their primary role is in cellular waste management and nutrient recycling. *Cytosolic cysteine proteases* - **Cytosolic cysteine proteases**, such as calpains and caspases, are crucial for various cellular processes including apoptosis, but they do not typically play a direct role in the metabolic activation of procarcinogens or the genotoxic events leading to chemical-induced liver cancer. - Their functions are generally related to protein turnover and cell signaling. *Peroxisomal catalases* - **Peroxisomal catalases** are enzymes primarily responsible for decomposing **hydrogen peroxide** into water and oxygen, protecting the cell from oxidative damage. - While managing reactive oxygen species is vital, catalases are not involved in the metabolic activation of procarcinogens like aflatoxins; their role is more in detoxification of harmful byproducts.

Question 47: A 66-year-old man presents to your office for a regular checkup. His only current complaint is periodic difficulty falling asleep at night. He takes captopril and hydrochlorothiazide for hypertension, atorvastatin for hyperlipidemia, and aspirin for cardiovascular disease prevention. His past medical history is significant for tympanoplasty performed 8 years ago for tympanic membrane rupture after an episode of purulent otitis media and intussusception that required surgical intervention 10 years ago. He also had a severe anaphylactic reaction after his 2nd Tdap administration 3 years ago. His blood pressure is 145/90 mm Hg, heart rate is 88/min, respiratory rate is 12/min, and temperature is 36.4°C (97.5°F). Physical examination only reveals a laterally displaced point of maximum impulse. Blood analysis shows the following findings: Sodium: 139 mEq/L (139 mmol/L) Potassium: 5.0 mEq/L (5.0 mmol/L) Chloride: 100 mEq/L (100 mmol/L) Bicarbonate: 22 mEq/L (22 mmol/L) Albumin: 3.8 mg/dL (38 g/L) Urea nitrogen: 8 mg/dL (2.86 mmol/L) Creatinine: 2.1 mg/dL (0.185 mmol/L) Uric acid: 5.8 mg/dL (0.34 mmol/L) Calcium: 8.9 mg/dL (2.22 mmol/L) Glucose: 106 mg/dL (5.89 mmol/L) Total cholesterol: 254 mg/dL (5.57 mmol/L) Low-density lipoprotein: 58 mg/dL (1.5 mmol/L) High-density lipoprotein: 77 mg/dL (2.0 mmol/L) Triglycerides: 159 mg/dL (1.8 mmol/L) The patient is concerned about pneumococcal infection and has never been vaccinated against pneumococcus. He should receive pneumococcal vaccination today. Which of the following statements regarding contraindications to pneumococcal vaccination in this patient is correct?

A. He has a severe allergy to diphtheria toxoid, a component of PCV13.
B. He is currently experiencing a moderate to severe acute illness with fever.
C. He is severely immunocompromised and cannot receive live vaccines.
D. He has a known severe allergy to any component of the PCV13 vaccine.
E. None of the above are valid contraindications to vaccination in this patient. (Correct Answer)

Explanation: ***None of the above are valid contraindications to vaccination in this patient*** This patient **should receive pneumococcal vaccination today**. The correct answer recognizes that none of the listed concerns represent true contraindications. Let's analyze why each potential concern is NOT a valid contraindication: *He has a severe allergy to diphtheria toxoid, a component of PCV13* - The patient had anaphylaxis to **Tdap vaccine** (contains tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis) - **PCV13 uses CRM197 carrier protein**, a non-toxic mutant of diphtheria toxin, which is structurally different from diphtheria toxoid - **Allergy to diphtheria toxoid does not predict allergy to CRM197** - they are different proteins with different immunogenic properties - Clinical studies show patients with diphtheria toxoid allergy typically tolerate CRM197-conjugated vaccines safely - This is **not a contraindication** to PCV13 *He is currently experiencing a moderate to severe acute illness with fever* - **Temperature: 36.4°C (97.5°F) - completely afebrile and normal** - Only complaint: periodic difficulty sleeping (not an acute illness) - Vital signs are stable with no signs of systemic illness - Physical exam unremarkable except displaced PMI (chronic finding from hypertension/cardiomegaly) - **No acute illness is present** - vaccination should proceed today - Note: Only moderate to severe acute illness with fever is a contraindication; minor illnesses are not *He is severely immunocompromised and cannot receive live vaccines* - This patient has **no evidence of immunocompromise** from his medical history or medications - **Both PCV13 and PPSV23 are inactivated vaccines** - they can be safely administered to immunocompromised patients - In fact, immunocompromised status **strengthens the indication** for pneumococcal vaccination - This concern is irrelevant as pneumococcal vaccines are not live vaccines *He has a known severe allergy to any component of the PCV13 vaccine* - His Tdap anaphylaxis does not automatically indicate allergy to PCV13 components (different vaccine formulations) - No documented allergy to specific PCV13 components (polysaccharides, CRM197, or aluminum phosphate) - This is **not established** in this patient and therefore not a contraindication **Correct vaccination approach:** This 66-year-old patient with chronic kidney disease (creatinine 2.1 mg/dL) and cardiovascular disease should receive pneumococcal vaccination today. Per CDC guidelines for adults ≥65 years who have never received pneumococcal vaccine: **PCV20 alone OR PCV15 followed by PPSV23** (8 weeks later for immunocompetent, 8 weeks for immunocompromised).

Question 48: A 38-year-old man is brought to the emergency room because of diarrhea for 2 days. He has abdominal cramps and has also noticed a dark red tint to his stool. He returned from a trip to Mexico 3 weeks ago, where he completed a marathon. He has a history of mild anemia. He does not smoke and drinks 3–4 beers on weekends. He takes fish oil, a multivitamin, and iron supplements to improve his athletic performance. His temperature is 101.8°F (38.8°C), pulse is 65/min, and blood pressure is 120/75 mm Hg. Lungs are clear to auscultation. Cardiac examination shows no abnormalities. There is mild tenderness to palpation of the left lower quadrant without rebound or guarding. Laboratory studies show: Hematocrit 37.1% Leukocyte count 4,500/mm3 Platelet count 240,000/mm3 Serum Na+ 136 mEq/L K+ 4.5 mEq/L Cl- 102 mEq/L HCO3- 26 mEq/L Urea nitrogen 14 mg/dL Creatinine 1.2 mg/dL Stool culture demonstrates organisms with ingested erythrocytes. In addition to supportive therapy, which of the following is the most appropriate next step in management?

A. Metronidazole (Correct Answer)
B. Paromomycin
C. Serological tests
D. Reassurance only
E. Praziquantel

Explanation: ***Metronidazole*** - The patient's history of recent travel to **Mexico**, bloody diarrhea, abdominal cramps, and the presence of organisms with **ingested erythrocytes** in stool culture are highly indicative of **amoebic dysentery** caused by *Entamoeba histolytica*. - **Metronidazole** is the drug of choice for treating **invasive amoebiasis**, including amoebic dysentery and liver abscesses, by targeting the trophozoites in the intestinal wall and tissue. - Note: Complete treatment typically includes a **luminal agent** (paromomycin or iodoquinol) after metronidazole to eradicate intestinal cysts and prevent relapse. *Paromomycin* - **Paromomycin** is a **luminal amoebicide** used to eradicate cysts in the colon, either as **monotherapy for asymptomatic carriers** or as **follow-up therapy after metronidazole** in invasive disease. - However, as the **initial treatment** for acute invasive amoebiasis, metronidazole is preferred because paromomycin is poorly absorbed and does not effectively reach tissue-invasive trophozoites. *Serological tests* - **Serological tests** for *Entamoeba histolytica* can be useful for diagnosing **extra-intestinal amoebiasis** (e.g., amoebic liver abscess) or for confirming past exposure. - However, they are generally **not helpful for acute diagnosis** of amoebic dysentery, as antibodies may take time to develop and persist for long periods after infection. *Reassurance only* - This patient presents with an acute febrile illness, **bloody diarrhea**, and clear evidence of an **invasive pathogen** on stool culture. - Reassurance only would be **inappropriate** and potentially harmful given the risk of severe complications from untreated amoebic dysentery. *Praziquantel* - **Praziquantel** is an **anti-helminthic** drug used to treat infections caused by **flukes** (e.g., Schistosoma, Clonorchis) and **tapeworms** (e.g., Taenia). - It has no activity against **protozoal infections** like *Entamoeba histolytica*.

Question 49: A healthy 34-year-old woman comes to the physician for advice on UV protection. She works as an archaeologist and is required to work outside for extended periods of time. She is concerned about premature skin aging. The physician recommends sun-protective clothing and sunscreen. In order to protect effectively against photoaging, the sunscreen should contain which of the following active ingredients?

A. Zinc oxide (Correct Answer)
B. Vitamin E
C. Para-aminobenzoic acid
D. Trimethoprim/sulfamethoxazole
E. Trolamine salicylate

Explanation: **Zinc oxide** - **Zinc oxide** is a physical sunscreen that provides broad-spectrum protection by **blocking both UVA and UVB rays**. - **UVA rays** are primarily responsible for **photoaging**, and physical blockers like zinc oxide are highly effective against them. *Vitamin E* - **Vitamin E** is an antioxidant that helps prevent cellular damage from free radicals, but it does **not provide direct protection against UV radiation** as a primary sunscreen ingredient. - While commonly used in skincare for its **antioxidant properties**, it is not an active UV-blocking agent. *Para-aminobenzoic acid* - **Para-aminobenzoic acid (PABA)** is an older chemical sunscreen ingredient that primarily **blocks UVB rays**. - It is often **associated with allergic reactions** and photosensitivity, and does not offer sufficient UVA protection for broad-spectrum coverage. *Trimethoprim/sulfamethoxazole* - **Trimethoprim/sulfamethoxazole** is an antibiotic combination used to treat various infections and has **no role in UV protection**. - It is a medication and not an ingredient found in sunscreens for UV blocking. *Trolamine salicylate* - **Trolamine salicylate** is a topical analgesic ingredient often found in pain-relief creams and is **not an active sunscreen agent**. - It has **no UV filtering properties** and does not protect against sun damage or photoaging.

Question 50: A 3-year-old girl with cystic fibrosis is brought to the physician for a follow-up examination. Her mother has noticed that the child has had multiple falls over the past 4 months while walking, especially in the evening. Her current medications include pancreatic enzyme supplements, an albuterol inhaler, and acetylcysteine. She is at the 10th percentile for height and the 5th percentile for weight. Examination shows dry skin, and cone shaped elevated papules on the trunk and extremities. There is an irregularly shaped foamy gray patch on the left conjunctiva. The remainder of the examination shows no abnormalities. Which of the following is the most appropriate next step in management?

A. Administer niacin
B. Administer riboflavin
C. Administer vitamin A (Correct Answer)
D. Administer zinc
E. Administer lutein

Explanation: ***Administer vitamin A*** - The patient's symptoms, including **night blindness** (falls in the evening), **dry skin**, **follicular hyperkeratosis** (cone-shaped elevated papules), and **Bitot spots** (foamy gray patch on conjunctiva), are classic signs of **vitamin A deficiency**. - **Cystic Fibrosis** patients are prone to **fat-soluble vitamin deficiencies** (A, D, E, K) due to pancreatic insufficiency and malabsorption. *Administer niacin* - **Niacin (B3) deficiency** causes **pellagra**, characterized by the "4 Ds": **dermatitis**, **diarrhea**, **dementia**, and **death**. These symptoms are not present in this patient. - While cystic fibrosis can sometimes lead to general malabsorption, specific signs of pellagra are absent. *Administer riboflavin* - **Riboflavin (B2) deficiency** typically presents with **chelosis** (cracked lips), **angular stomatitis**, **glossitis**, and **seborrheic dermatitis**. - The patient's symptoms do not align with riboflavin deficiency. *Administer zinc* - **Zinc deficiency** can cause **growth retardation**, **diarrhea**, **alopecia**, and characteristic **periorificial and acral dermatitis**. - Although malabsorption in cystic fibrosis can affect zinc levels, the specific constellation of symptoms points more directly to vitamin A deficiency. *Administer lutein* - **Lutein** is a carotenoid important for eye health, but its deficiency does not cause the widespread systemic symptoms related to night blindness and dermatological changes seen in this patient. - It's not a primary vitamin, and its deficiency is not managed as acutely as vitamin A deficiency presenting with these severe symptoms.

Question 51: A 23-year-old woman presents to her primary care provider complaining of diarrhea. She reports a 2 month history of 3-4 bloody stools per day as well as 10 pounds of unexpected weight loss. She has also developed intermittent mild gnawing lower abdominal pain. Her past medical history is unremarkable. She takes no medications and denies any drug allergies. Her family history is notable for colon cancer in her maternal aunt, rheumatoid arthritis in her paternal aunt, and Sjogren syndrome in her paternal grandmother. Her temperature is 99.1°F (37.3°C), blood pressure is 120/85 mmHg, pulse is 85/min, and respirations are 18/min. On exam, she has mild hypogastric tenderness to palpation. A stool guaiac test is positive. Flexible sigmoidoscopy demonstrates hyperemic and friable rectal mucosa. She is started on a medication to address her condition but presents to her physician one week later with a severe sunburn and skin itchiness following limited exposure to sunlight. Which of the following is the mechanism of action of the medication she received?

A. Dihydrofolate reductase inhibitor
B. NF-kB inhibitor (Correct Answer)
C. COX inhibitor
D. Calcineurin inhibitor
E. DNA gyrase inhibitor

Explanation: ***NF-κB inhibitor*** - The patient's symptoms (bloody diarrhea, weight loss, abdominal pain, friable rectal mucosa) are highly suggestive of **ulcerative colitis** - **Sulfasalazine**, a 5-aminosalicylate (5-ASA) drug, is a common first-line treatment for mild-to-moderate ulcerative colitis - The active metabolite **mesalamine** exerts its anti-inflammatory effects primarily through **inhibition of NF-κB**, a key transcription factor that regulates inflammatory cytokine production - The **sulfapyridine** component is responsible for the photosensitivity reaction (severe sunburn and skin itchiness after sun exposure) that this patient experienced - Other mechanisms include prostaglandin inhibition, free radical scavenging, and modulation of leukocyte function, but **NF-κB inhibition is the predominant mechanism** *COX inhibitor* - While mesalamine does have some cyclooxygenase (COX) inhibitory activity and reduces prostaglandin synthesis, this is a **secondary mechanism** of action - The primary anti-inflammatory effect of 5-ASA drugs in inflammatory bowel disease is through **NF-κB inhibition**, not COX inhibition - Traditional NSAIDs (pure COX inhibitors) can actually worsen IBD symptoms, highlighting that COX inhibition alone is not the therapeutic mechanism *Dihydrofolate reductase inhibitor* - This mechanism describes **methotrexate**, an immunosuppressant used in more severe or refractory cases of inflammatory bowel disease, but not typically as a first-line agent - Methotrexate is not associated with photosensitivity reactions in the manner seen with sulfasalazine *Calcineurin inhibitor* - **Calcineurin inhibitors** such as **cyclosporine** or **tacrolimus** are potent immunosuppressants typically reserved for severe, refractory cases of inflammatory bowel disease - Their side effect profile includes nephrotoxicity, hypertension, and hirsutism, but not the characteristic photosensitivity seen with sulfasalazine *DNA gyrase inhibitor* - **DNA gyrase inhibitors** (fluoroquinolones) are antibiotics used to treat bacterial infections - These are not used as primary treatment for inflammatory bowel disease, which is an immune-mediated condition - While fluoroquinolones can cause photosensitivity, they would not be prescribed for ulcerative colitis management

Question 52: A 6-year-old boy is brought to the physician because of headache, cough, runny nose, and a low-grade fever since waking up that morning. He has been healthy except for a urinary tract infection one week ago that has resolved with trimethoprim-sulfamethoxazole therapy. Both parents have a history of allergic rhinitis. His temperature is 37.8°C (100°F). Physical exam shows rhinorrhea and tenderness over the frontal and maxillary sinuses. There is cervical lymphadenopathy. Laboratory studies show: Hemoglobin 14.2 g/dL Leukocyte count 2,700/mm3 Segmented neutrophils 30% Bands 1% Eosinophils 4% Basophils 0% Lymphocytes 56% Monocytes 9% Platelet count 155,000/mm3 Which of the following is the most likely underlying cause of this patient's symptoms?

A. CMV infection
B. EBV infection
C. Acute lymphocytic leukemia
D. Medication side effect (Correct Answer)
E. Acute myelogenous leukemia

Explanation: ***Medication side effect*** - The patient's recent **trimethoprim-sulfamethoxazole (TMP-SMX)** treatment and current **leukopenia** (WBC 2,700/mm³, normal 5,000-10,000/mm³) with **neutropenia** (absolute neutrophil count ~840/mm³) strongly suggest **drug-induced bone marrow suppression**. - TMP-SMX is a folate antagonist known to cause dose-dependent bone marrow suppression, particularly affecting neutrophils and occasionally platelets. The platelet count (155,000/mm³) is at the lower limit of normal, which may represent early marrow effect. - While the patient's current symptoms (rhinorrhea, cough, sinus tenderness, low-grade fever) suggest an **acute viral upper respiratory infection**, the question asks for the "most likely underlying cause." The **leukopenia with neutropenia** is the most significant abnormal finding and represents the drug effect that predisposes to or complicates infections. - The combination of recent antibiotic exposure and cytopenias makes medication side effect the primary diagnosis. *CMV infection* - CMV can cause **leukopenia**, but typically presents with more prominent constitutional symptoms including prolonged fever, malaise, hepatosplenomegaly, and atypical lymphocytosis. - The acute onset of URI symptoms and temporal relationship to antibiotic use makes drug-induced marrow suppression more likely. *EBV infection* - EBV (infectious mononucleosis) characteristically causes **lymphocytosis with atypical lymphocytes**, not leukopenia. - Classic features include **pharyngitis**, **posterior cervical lymphadenopathy**, **splenomegaly**, and fatigue, which are not present here. - The lymphocyte percentage (56%) is within normal range for age, not elevated. *Acute lymphocytic leukemia* - **ALL** would present with more severe constitutional symptoms (high fever, bone pain, significant fatigue) and typically shows **circulating blasts** on peripheral smear. - The cytopenias in ALL are usually more profound (severe anemia, marked thrombocytopenia <50,000/mm³). - The absence of blasts in the differential and relatively preserved hemoglobin (14.2 g/dL) argue against leukemia. *Acute myelogenous leukemia* - **AML** presents with severe symptoms including fatigue, bleeding diathesis, and recurrent infections. - Peripheral smear typically shows **myeloblasts** with Auer rods in some cases. - The patient's mild symptoms, absence of blasts, and normal hemoglobin make AML highly unlikely.

Question 53: A 54-year-old woman is brought to the emergency department by a nurse 30 minutes after receiving scheduled radiation therapy for papillary thyroid cancer. After the radioisotope was ingested, the physician realized that a much larger fixed dose was given instead of the appropriate dose based on radiation dosimetry. Which of the following pharmacotherapies should be administered immediately to prevent complications from this exposure?

A. Dexrazoxane
B. Methimazole
C. Propylthiouracil
D. Potassium iodide (Correct Answer)
E. Mercaptoethanesulfonate

Explanation: ***Potassium iodide*** - **Potassium iodide (KI)** is the immediate treatment for **radioactive iodine exposure** and works by saturating the thyroid gland with stable, non-radioactive iodine. - This **competitive inhibition** prevents the uptake of radioactive iodine-131 by the thyroid, thereby reducing the risk of radiation-induced thyroid damage and cancer. - **Timing is critical**: KI is most effective when given immediately (within hours) after exposure to radioactive iodine. - The patient received an overdose of **radioactive iodine-131** (commonly used for papillary thyroid cancer treatment), making immediate KI administration the definitive thyroid protective measure. *Dexrazoxane* - **Dexrazoxane** is a **cardioprotective agent** used to reduce cardiotoxicity associated with **anthracycline chemotherapy** (e.g., doxorubicin). - It chelates iron and prevents formation of anthracycline-iron complexes that generate free radicals. - It has no role in preventing complications from radioactive iodine exposure. *Methimazole* - **Methimazole** is an **antithyroid drug** that inhibits thyroid peroxidase, thereby blocking the **iodination and coupling of tyrosyl residues** in thyroid hormone synthesis. - While it reduces thyroid hormone production, it does **not prevent uptake** of radioactive iodine by the thyroid gland. - It is ineffective for acute radiation protection in this scenario. *Propylthiouracil* - **Propylthiouracil (PTU)** is another **antithyroid drug** that inhibits thyroid peroxidase and also blocks peripheral conversion of **T4 to T3**. - Like methimazole, PTU does **not prevent radioactive iodine uptake** by the thyroid. - It is not indicated for acute radioactive iodine exposure management. *Mercaptoethanesulfonate* - **Mercaptoethanesulfonate (MESNA)** is a **uroprotective agent** used to prevent hemorrhagic cystitis caused by **oxazaphosphorine chemotherapy agents** (cyclophosphamide and ifosfamide). - MESNA binds to and detoxifies acrolein, the toxic metabolite responsible for bladder toxicity. - It has no role in managing radioactive iodine exposure.

Question 54: A 13-year-old Caucasian male presents with his father to the pediatrician’s office complaining of left lower thigh pain. He reports slowly progressive pain over the distal aspect of his left thigh over the past three months. He denies any recent trauma to the area. His temperature is 100.9°F (38.3°C). On exam, there is swelling and tenderness overlying the inferior aspect of the left femoral diaphysis. Laboratory evaluation is notable for an elevated white blood cell (WBC) count and erythrocyte sedimentation rate (ESR). Biopsy of the lesion demonstrates sheets of monotonous small round blue cells with minimal cytoplasm. He is diagnosed and started on a medication that inhibits transcription by intercalating into DNA at the transcription initiation complex. Which of the following adverse events will this patient be at highest risk for following initiation of this medication?

A. Peripheral neuropathy
B. Bone marrow suppression (Correct Answer)
C. Gingival hyperplasia
D. Pulmonary fibrosis
E. Hemorrhagic cystitis

Explanation: ***Bone marrow suppression*** - The medication described, which inhibits transcription by intercalating into DNA at the transcription initiation complex, is likely **dactinomycin (actinomycin D)**. - **Bone marrow suppression** is a common and severe adverse effect of dactinomycin, leading to issues like **neutropenia** and **thrombocytopenia**. *Peripheral neuropathy* - This is a common side effect of **vinca alkaloids** (e.g., vincristine, vinblastine) and **taxanes**, which are not described by the mechanism of action given. - Dactinomycin does not typically cause significant peripheral neuropathy. *Gingival hyperplasia* - **Gingival hyperplasia** is a known side effect of medications such as **cyclosporine**, **phenytoin**, and **calcium channel blockers** like nifedipine. - It is not associated with dactinomycin. *Pulmonary fibrosis* - This is a serious adverse effect of certain chemotherapeutic agents like **bleomycin** and **busulfan**, and other drugs like **amiodarone** and **methotrexate**. - Dactinomycin is not primarily associated with pulmonary fibrosis. *Hemorrhagic cystitis* - **Hemorrhagic cystitis** is a classic adverse effect of **cyclophosphamide** and **ifosfamide**, caused by the metabolite **acrolein**. - This adverse event is prevented by co-administration of **MESNA**, and is not a common side effect of dactinomycin.

Question 55: A 60-year-old female presents to her primary care physician complaining of bloating and fatigue over the past year. On examination, she has abdominal distension and ascites. Abdominal imaging reveals a mass-like lesion affecting the left ovary. A biopsy of the lesion demonstrates serous cystadenocarcinoma. She is subsequently started on a chemotherapeutic medication known to stabilize polymerized microtubules. Which of the following complications should this patient be monitored for following initiation of this medication?

A. Peripheral neuropathy (Correct Answer)
B. Pulmonary fibrosis
C. Acoustic nerve damage
D. Hemorrhagic cystitis
E. Cardiotoxicity

Explanation: ***Peripheral neuropathy*** - The chemotherapeutic medication described, which stabilizes **polymerized microtubules**, is likely a **taxane** (e.g., paclitaxel, docetaxel), often used for ovarian cancer. - Taxanes are well-known to cause **dose-dependent peripheral neuropathy** due to their effects on microtubule dynamics in neuronal axons. *Pulmonary fibrosis* - **Pulmonary fibrosis** is a significant side effect associated with certain chemotherapeutic agents like **bleomycin** or **busulfan**, but not typically with taxanes. - Monitoring for this would involve assessing breath sounds, oxygen saturation, and potentially imaging for interstitial changes. *Acoustic nerve damage* - **Acoustic nerve damage** and ototoxicity are characteristic side effects of **platinum-based chemotherapy agents** (e.g., cisplatin), which are also used in ovarian cancer but have a different mechanism of action than microtubule stabilizers. - This typically manifests as **tinnitus** or **hearing loss**. *Hemorrhagic cystitis* - **Hemorrhagic cystitis** is a common and severe side effect of **cyclophosphamide** and **ifosfamide**, alkylating agents, due to the accumulation of their metabolite **acrolein** in the bladder. - It is not associated with microtubule-stabilizing agents like taxanes. *Cardiotoxicity* - **Cardiotoxicity**, including dilated cardiomyopathy, is a serious side effect primarily associated with **anthracyclines** (e.g., doxorubicin), which generate free radicals and damage cardiac myocytes. - While some taxanes can cause cardiovascular effects, severe cardiotoxicity like that seen with anthracyclines is not their primary or most concerning side effect.

Question 56: A 26-year-old man comes to the emergency department because of a 1-week history of worsening fatigue, nausea, and vomiting. Six weeks ago, he was diagnosed with latent tuberculosis and appropriate low-dose pharmacotherapy was initiated. Physical examination shows right upper quadrant tenderness and scleral icterus. Laboratory studies show elevated aminotransferases. Impaired function of which of the following pharmacokinetic processes is the most likely explanation for this patient's symptoms?

A. Acetylation (Correct Answer)
B. Glucuronidation
C. Hydrolysis
D. Sulfation
E. Reduction

Explanation: ***Acetylation*** - This patient is exhibiting symptoms of **hepatotoxicity** (fatigue, nausea, vomiting, RUQ tenderness, scleral icterus, elevated aminotransferases) after starting low-dose pharmacotherapy for latent tuberculosis. The most common drug used for latent TB is **isoniazid**, which is primarily metabolized by **N-acetylation**. - Impaired acetylation, particularly in **slow acetylators**, can lead to higher plasma concentrations of isoniazid and its toxic metabolites, increasing the risk of **drug-induced liver injury**. *Glucuronidation* - **Glucuronidation** is a Phase II metabolic pathway that conjugates drugs with **glucuronic acid** to increase water solubility and facilitate excretion. - While important for the metabolism of many drugs and endogenous substances (e.g., bilirubin), it is not the primary mechanism of metabolism or the main pathway implicated in the hepatotoxicity of **isoniazid**. *Hydrolysis* - **Hydrolysis** is a chemical reaction in which water is used to break down a compound, often involving ester or amide bonds. - This process is not the primary metabolic pathway for **isoniazid**, nor is impaired hydrolysis a common cause of its hepatotoxicity. *Sulfation* - **Sulfation** is a Phase II metabolic reaction that conjugates drugs with a **sulfate group**, typically for detoxification and excretion. - While various drugs undergo sulfation, it is not the dominant metabolic pathway for **isoniazid**, and impaired sulfation is not typically associated with isoniazid-induced hepatotoxicity. *Reduction* - **Reduction** reactions involve the gain of electrons or hydrogen atoms, or the loss of oxygen, and are part of drug metabolism for certain compounds. - However, reduction is not the primary clearance mechanism for **isoniazid**, and abnormal reduction is not commonly implicated in its hepatotoxic effects.

Question 57: A 67-year-old male with a past medical history of diabetes type II, obesity, and hyperlipidemia presents to the general medical clinic with bilateral hearing loss. He also reports new onset vertigo and ataxia. The symptoms started a day after undergoing an uncomplicated cholecystectomy. If a drug given prophylactically just prior to surgery has caused this patient’s symptoms, what is the mechanism of action of the drug?

A. Formation of free radical toxic metabolites that damage DNA
B. Inhibition of the formation of the translation initiation complex (Correct Answer)
C. Inhibition of DNA gyrase
D. Inhibition of cell wall synthesis
E. Inhibition of DNA-dependent RNA polymerase

Explanation: **Correct: Inhibition of the formation of the translation initiation complex** - The symptoms of **bilateral hearing loss**, **vertigo**, and **ataxia** point to **ototoxicity** and **vestibulotoxicity**, which are classic side effects of **aminoglycoside antibiotics**. - Aminoglycosides, such as gentamicin, are known to **inhibit bacterial protein synthesis** by binding to the **30S ribosomal subunit**, thereby **inhibiting the formation of the translation initiation complex**. They are sometimes used prophylactically, though less commonly for cholecystectomy. *Incorrect: Formation of free radical toxic metabolites that damage DNA* - This mechanism is characteristic of **nitrofurans** (e.g., nitrofurantoin) and some **antimalarials**, which are not typically used for surgical prophylaxis. - While these drugs can cause various adverse effects, this specific mechanism does not lead to the described triad of ototoxicity and vestibulotoxicity. *Incorrect: Inhibition of DNA gyrase* - This is the mechanism of action for **fluoroquinolone antibiotics** (e.g., ciprofloxacin, levofloxacin). - While fluoroquinolones can cause adverse effects like tendinopathy and CNS disturbances, they are not typically associated with the pronounced ototoxicity and vestibulotoxicity seen in this patient. *Incorrect: Inhibition of cell wall synthesis* - This is the mechanism of action for **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) and **vancomycin**, which are common choices for surgical prophylaxis. - Though some of these drugs can have side effects (e.g., vancomycin's "red man syndrome" or ototoxicity in specific cases), the combination of bilateral hearing loss, vertigo, and ataxia is not their characteristic adverse effect profile. *Incorrect: Inhibition of DNA-dependent RNA polymerase* - This is the mechanism of action for **rifamycins** (e.g., rifampin). - Rifampin is primarily used for tuberculosis and some other serious infections, not typically for routine surgical prophylaxis, and its side effect profile does not include this specific constellation of ototoxicity and vestibulotoxicity.

Question 58: A 70-year-old woman presents with numbness and tingling that is worse in the soles of her feet. She says that symptoms started a few weeks ago and have progressively worsened. She also complains of mild nausea and white lines on her fingernails. Past medical history is significant for diabetes mellitus type 2, managed with metformin. Her last HbA1c was 5.8%. The patient denies any changes in her vision, chest pain, or palpitations. She says she lives near an industrial area that was in the newspaper for leaking waste into the groundwater but she can’t remember the details. She also says she spends a lot of her free time in her garden. On physical examination, there is decreased fine touch, temperature, and vibrational sensation in the extremities bilaterally Strength is reduced symmetrically 4 out of 5 in all limbs along with reduced (1+) deep tendon reflexes. Which of the following is the best treatment option for this patient?

A. Tight control of her diabetes mellitus by adding insulin
B. Trientine
C. Calcium disodium edetate (EDTA)
D. Penicillamine
E. Dimercaprol (Correct Answer)

Explanation: ***Dimercaprol*** - The patient's symptoms, including **peripheral neuropathy** (numbness, tingling, decreased sensation, reduced strength and reflexes), **nausea**, and **Mees\' lines** (white lines on fingernails), are highly suggestive of **arsenic poisoning**. - **Dimercaprol** is a chelating agent effective in treating heavy metal poisoning, including **arsenic**, by forming stable complexes that are then excreted. *Tight control of her diabetes mellitus by adding insulin* - While the patient has diabetes, her **HbA1c of 5.8%** indicates excellent glycemic control, making diabetic neuropathy less likely to be the primary cause of her acute, worsening symptoms. - The presence of **Mees' lines** and the environmental exposure history strongly point away from uncomplicated diabetic neuropathy. *Trientine* - **Trientine** is a chelating agent primarily used to treat **Wilson's disease**, which involves copper overload. - The patient's symptoms do not align with copper toxicity, and there is no indication for trientine use. *Calcium disodium edetate (EDTA)* - **Calcium disodium EDTA** is primarily used to treat **lead poisoning** and certain other heavy metal toxicities. - While a chelating agent, it is not the first-line treatment for arsenic poisoning and lacks the same efficacy as dimercaprol for this specific condition. *Penicillamine* - **Penicillamine** is another chelating agent used for various conditions, including **Wilson's disease**, **rheumatoid arthritis**, and sometimes **lead poisoning**. - It is not the preferred or most effective treatment for acute arsenic poisoning.

Question 59: A 22-year-old woman comes to the physician because of abdominal pain and diarrhea for 2 months. The pain is intermittent, colicky and localized to her right lower quadrant. She has anorexia and fears eating due to the pain. She has lost 4 kg (8.8 lb) during this time. She has no history of a serious illness and takes no medications. Her temperature is 37.8°C (100.0°F), blood pressure 125/65 mm Hg, pulse 75/min, and respirations 14/min. An abdominal examination shows mild tenderness of the right lower quadrant on deep palpation without guarding. Colonoscopy shows small aphthous-like ulcers in the right colon and terminal ileum. Biopsy from the terminal ileum shows noncaseating granulomas in all layers of the bowel wall. Which of the following is the most appropriate pharmacotherapy at this time?

A. Budesonide (Correct Answer)
B. Azathioprine
C. Ciprofloxacin
D. Metronidazole
E. Rectal mesalamine

Explanation: ***Budesonide*** - This patient presents with symptoms and findings (RLQ pain, aphthous ulcers, noncaseating granulomas in the terminal ileum) consistent with **Crohn's disease** isolated to the **ileum and right colon**. - **Budesonide** is a glucocorticoid with high first-pass metabolism, making it effective for localized ileal and right colonic Crohn's disease with fewer systemic side effects than prednisone. *Azathioprine* - **Azathioprine** is an immunomodulator used for maintaining remission in moderate to severe Crohn's disease, not typically for acute exacerbations as first-line monotherapy. - Its onset of action is slow (several weeks to months), making it unsuitable for immediate symptom control. *Ciprofloxacin* - **Ciprofloxacin** is an antibiotic mainly used when there is concern for bacterial overgrowth, abscess, or perianal disease in Crohn's, none of which are explicitly indicated here. - There is no evidence suggesting a primary bacterial infection as the cause of her current symptoms. *Metronidazole* - **Metronidazole** is an antibiotic often used for Crohn's disease with perianal involvement or fistulas, and sometimes for active colonic disease, but less effective for ileal involvement. - Like ciprofloxacin, it's not the primary treatment for uncomplicated flare of ileocolonic Crohn's. *Rectal mesalamine* - **Rectal mesalamine** is an aminosalicylate primarily used for mild to moderate **ulcerative colitis**, particularly proctitis or left-sided colitis due to its topical action. - It is ineffective for Crohn's disease involving the terminal ileum and right colon, as it would not reach this location in sufficient concentration.

Question 60: A research group wants to assess the safety and toxicity profile of a new drug. A clinical trial is conducted with 20 volunteers to estimate the maximum tolerated dose and monitor the apparent toxicity of the drug. The study design is best described as which of the following phases of a clinical trial?

A. Phase 0
B. Phase III
C. Phase V
D. Phase II
E. Phase I (Correct Answer)

Explanation: ***Phase I*** - **Phase I clinical trials** involve a small group of healthy volunteers (typically 20-100) to primarily assess **drug safety**, determine a safe dosage range, and identify side effects. - The main goal is to establish the **maximum tolerated dose (MTD)** and evaluate the drug's pharmacokinetic and pharmacodynamic profiles. *Phase 0* - **Phase 0 trials** are exploratory studies conducted in a very small number of subjects (10-15) to gather preliminary data on a drug's **pharmacodynamics and pharmacokinetics** in humans. - They involve microdoses, not intended to have therapeutic effects, and thus cannot determine toxicity or MTD. *Phase III* - **Phase III trials** are large-scale studies involving hundreds to thousands of patients to confirm the drug's **efficacy**, monitor side effects, compare it to standard treatments, and collect information that will allow the drug to be used safely. - These trials are conducted after safety and initial efficacy have been established in earlier phases. *Phase V* - "Phase V" is not a standard, recognized phase in the traditional clinical trial classification (Phase 0, I, II, III, IV). - This term might be used in some non-standard research contexts or for post-marketing studies that go beyond Phase IV surveillance, but it is not a formal phase for initial drug development. *Phase II* - **Phase II trials** involve several hundred patients with the condition the drug is intended to treat, focusing on **drug efficacy** and further evaluating safety. - While safety is still monitored, the primary objective shifts to determining if the drug works for its intended purpose and at what dose.

Question 61: A 3-year-old boy is brought to his pediatrician by his mother when he developed redness, burning, itching, and exquisite pain all over his arms, lower legs, neck, and face. The mother states that she just recently began taking him to the local playground in the afternoons. She reports that she applied liberal amounts of sunscreen before and during the time outside. She states that they were at the playground for 30 minutes to 1 hour each day for the last 3 days. The patient has experienced prior episodes of redness and pain after being outdoors, but they were relatively minor and resolved within 12 hours. She says his current presentation is much more severe with more exquisite pain than in the past. The patient's vital signs are as follows: T 37.2 C, HR 98, BP 110/62, RR 16, and SpO2 99%. Physical examination reveals edema, erythema, and petechiae over the patient's face, neck, arms, and lower legs. No blistering or scarring of the skin is noted. Which of the following is the best treatment option for this patient's condition?

A. Start therapeutic phlebotomy
B. Recommend use of a high SPF topical sunscreen
C. Prescribe chloroquine
D. Initiate oral beta carotene
E. Begin dexamethasone taper (Correct Answer)

Explanation: ***Begin dexamethasone taper*** - The patient's symptoms (redness, burning, itching, exquisite pain, edema, erythema, petechiae in sun-exposed areas) following sun exposure are highly suggestive of **erythropoietic protoporphyria (EPP)**, which is characterized by painful photosensitivity. - While supportive care and sun protection are crucial, **oral corticosteroids** like dexamethasone can provide significant relief during acute, severe phototoxic reactions by reducing inflammation. A taper is appropriate to manage the acute exacerbation. *Start therapeutic phlebotomy* - **Therapeutic phlebotomy** is indicated in conditions like **hemochromatosis** to reduce iron overload. - It is not a treatment for porphyrias, and specifically not for erythropoietic protoporphyria. *Recommend use of a high SPF topical sunscreen* - While **sunscreen** is generally recommended for sun protection, it is typically **ineffective** in preventing the reactions seen in photosensitivity disorders like EPP because the relevant light wavelengths (visible light) often penetrate, and the underlying mechanism is not superficial UV damage. - The patient's mother already applied liberal amounts of sunscreen, yet the symptoms occurred, further suggesting it's not adequate for this condition. *Prescribe chloroquine* - **Chloroquine** (and hydroxychloroquine) is used in some porphyrias, specifically **porphyria cutanea tarda (PCT)**, to chelate and remove porphyrins. - However, it can **exacerbate** EPP due to its effects on porphyrin metabolism and liver function, making it contraindicated in this condition. *Initiate oral beta carotene* - **Oral beta-carotene** is sometimes used as a photoprotective agent in certain photosensitivity disorders, including EPP, to increase the threshold for light exposure. - While it can be a part of long-term management, it is primarily a **prophylactic** measure and is generally **not effective for treating acute, severe exacerbations** or providing rapid relief from acute pain and inflammation.

Question 62: A 36-year-old woman comes to the physician because of prolonged stiffness in the morning and progressive pain and swelling of her wrists and hands over the past 4 months. Examination shows bilateral swelling and mild tenderness of the wrists and the second, third, and fourth metacarpophalangeal joints. Her range of motion is limited by pain. Serum studies show elevated anti-cyclic citrullinated peptide antibodies. Treatment with methotrexate is begun. At a follow-up examination, her serum aspartate aminotransferase (AST) concentration is 75 U/L and her serum alanine aminotransferase (ALT) concentration is 81 U/L. Which of the following substances is essential for the function of these enzymes?

A. Thiamine
B. Pyridoxine (Correct Answer)
C. Folic acid
D. Riboflavin
E. Niacin

Explanation: ***Pyridoxine*** - **Pyridoxine (Vitamin B6)** is a crucial **cofactor** for **aminotransferase enzymes** like AST and ALT, functioning as **pyridoxal phosphate (PLP)**. - In the context of **methotrexate treatment**, monitoring liver enzymes is essential due to potential **hepatotoxicity**, and disturbances in pyridoxine metabolism can impact enzyme activity. *Thiamine* - **Thiamine (Vitamin B1)** is essential for enzymes involved in **carbohydrate metabolism**, particularly in the form of **thiamine pyrophosphate (TPP)**. - It plays a primary role in reactions such as those catalyzed by **pyruvate dehydrogenase** and **alpha-ketoglutarate dehydrogenase**, not aminotransferases. *Folic acid* - **Folic acid (Vitamin B9)** is primarily involved in **one-carbon metabolism**, including **DNA synthesis** and repair. - It is not a cofactor for AST or ALT; however, **leucovorin (folinic acid)** is often co-administered with methotrexate to mitigate its side effects. *Riboflavin* - **Riboflavin (Vitamin B2)** is a precursor for **flavin adenine dinucleotide (FAD)** and **flavin mononucleotide (FMN)**, which are cofactors for **redox reactions**. - Enzymes like **succinate dehydrogenase** and **acyl-CoA dehydrogenase** require riboflavin, but not AST or ALT. *Niacin* - **Niacin (Vitamin B3)** is a precursor for **nicotinamide adenine dinucleotide (NAD+)** and **nicotinamide adenine dinucleotide phosphate (NADP+)**, which are vital for many **dehydrogenase reactions**. - These coenzymes are crucial for **energy metabolism**, but not directly for the catalytic activity of aminotransferases.

Question 63: A 45-year-old homeless man presents to the emergency department with a 1-week history of an intensely pruritic, red rash on his hands, wrists, and finger webs. The itching is worse at night. Physical examination reveals small, erythematous papules and burrows. A topical drug with which of the following mechanisms of action is most likely to be effective in treating this condition?

A. Increase in keratinocyte turnover
B. Inhibition of histamine-1 receptors
C. Decrease in peptidoglycan synthesis
D. Inhibition of nuclear factor-κB
E. Binding to sodium channels (Correct Answer)

Explanation: ***Binding to sodium channels*** - The clinical presentation of **intensely pruritic rash**, especially worse at night, with **burrows** on hands, wrists, and finger webs, is highly suggestive of **scabies**. - Scabies is caused by the mite *Sarcoptes scabiei*, and treatment often involves **permethrin**, which acts by **binding to sodium channels** in the mite's nervous system, leading to paralysis and death. *Increase in keratinocyte turnover* - This mechanism of action is characteristic of drugs used to treat conditions like **psoriasis**, where the goal is to reduce rapid skin cell proliferation. - It is not relevant for parasitic infestations like scabies, which require an agent to directly kill the mites. *Inhibition of histamine-1 receptors* - Antihistamines, which block H1 receptors, are used to alleviate **pruritus** associated with allergic reactions or other inflammatory skin conditions. - While they can help with the *symptom* of itching, they do not address the underlying *cause* of scabies (the mite infestation itself). *Decrease in peptidoglycan synthesis* - This mechanism is characteristic of **antibiotics** like **penicillins** and **cephalosporins**, which target the bacterial cell wall. - It is effective against bacterial infections but has no utility in treating parasitic infestations like scabies, which are caused by arthropods, not bacteria. *Inhibition of nuclear factor-κB* - **NF-κB** is a protein complex that controls **transcription of DNA**, cytokine production, and cell survival, and its inhibition is often targeted in **inflammatory diseases** or cancers. - This mechanism is not directly involved in the eradication of scabies mites.

Question 64: An 8-year-old boy is brought to the physician because of a 1-day history of severe left hand pain. He has had similar painful episodes in the past that required hospitalization. Physical examination shows pale conjunctivae. There is tenderness on palpation of the wrist and the small joints of the left hand. Peripheral blood smear shows crescent-shaped erythrocytes. He is started on a pharmacologic agent that is known to cause macrocytosis. This drug causes an arrest in which of the following cell cycle phases?

A. S phase (Correct Answer)
B. G0 phase
C. G2 phase
D. M phase
E. G1 phase

Explanation: ***S phase*** - This patient presents with **sickle cell disease** given the history of recurrent severe pain episodes, pale conjunctivae (suggesting anemia), and **crescent-shaped erythrocytes** on peripheral blood smear. - The pharmacologic agent that causes **macrocytosis** and is used in sickle cell disease is **hydroxyurea** through increasing **fetal hemoglobin**; it primarily works by inhibiting **ribonucleotide reductase**, an enzyme essential for **DNA synthesis**, thereby arresting cells in the **S phase**. *G0 phase* - The **G0 phase** is a resting phase where cells are not actively dividing or preparing to divide. - Hydroxyurea targets rapidly dividing cells by interfering with DNA replication, so it does not primarily arrest cells in the inactive G0 phase. *G2 phase* - The **G2 phase** is the growth phase where the cell checks its DNA and prepares for mitosis. - While hydroxyurea can indirectly affect the G2/M checkpoint, its direct mechanism of action is primarily in the S phase by preventing proper DNA synthesis. *M phase* - The **M phase** is the stage of cell division, including mitosis and cytokinesis. - Drugs that block the M phase typically interfere with **microtubule formation** (e.g., vinca alkaloids, taxanes), which is not the primary mechanism of hydroxyurea. *G1 phase* - The **G1 phase** is the initial growth phase where the cell grows and synthesizes proteins. - While cells must pass through G1 before entering S phase, hydroxyurea's direct DNA synthesis inhibition occurs during the S phase rather than preventing entry into S from G1.

Question 65: A 33-year-old woman presents to her local clinic in rural eastern India complaining of neck pain and fever. She reports a 4 day history of severe neck pain, neck stiffness, mild diarrhea, and fever. She has not taken her temperature. She works as a laborer and frequently carries heavy weights on her back. She is prescribed a medication and told to come back if her symptoms do not improve. Her symptoms resolve after a couple days. Six months later, she gives birth to a newborn male at 34 weeks gestation. His temperature is 97.8°F (36.6°C), blood pressure is 90/55 mmHg, pulse is 110/min, and respirations are 24/min. On examination, the baby is irritable with a weak cry. Ashen gray cyanosis is noted diffusely. What is the mechanism of action of the drug responsible for this child's presentation?

A. DNA-dependent RNA polymerase inhibitor
B. Dihydropteroate synthase inhibitor
C. DNA gyrase inhibitor
D. 30S ribosomal subunit inhibitor
E. 50S ribosomal subunit inhibitor (Correct Answer)

Explanation: ***50S ribosomal subunit inhibitor*** - The mother's symptoms (neck pain, stiffness, fever, mild diarrhea) and rapid improvement suggest a bacterial infection treated with an antibiotic. Given the newborn's presentation of **gray baby syndrome** (ashen gray cyanosis, irritability, weak cry, hypothermia, hypotension), the likely causative drug is **chloramphenicol**. - **Chloramphenicol** inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**, which can cause idiosyncratic toxicity in neonates due to underdeveloped glucuronidation enzymes needed for its metabolism. *DNA-dependent RNA polymerase inhibitor* - This mechanism describes drugs like **rifampin**, which is primarily used for **tuberculosis** and does not cause gray baby syndrome. - Rifampin's side effects include **red-orange discoloration** of bodily fluids and **hepatotoxicity**, which are distinct from the described neonatal symptoms. *Dihydropteroate synthase inhibitor* - This mechanism is characteristic of **sulfonamides** (e.g., sulfamethoxazole), which inhibit folic acid synthesis in bacteria. - Sulfonamides are associated with **kernicterus** in neonates (due to displacement of bilirubin from albumin), not gray baby syndrome. *DNA gyrase inhibitor* - This describes **fluoroquinolones** (e.g., ciprofloxacin), which block bacterial DNA replication and transcription. - Fluoroquinolones are generally **contraindicated in pregnancy and children** due to concerns about cartilage damage, but they do not cause gray baby syndrome. *30S ribosomal subunit inhibitor* - This mechanism is used by **tetracyclines** and **aminoglycosides**. - **Tetracyclines** can cause **tooth discoloration** and **bone growth inhibition** in children, while **aminoglycosides** are associated with **ototoxicity** and **nephrotoxicity**; neither causes gray baby syndrome.

Question 66: A 25-year-old man presents to the physician with 2 days of profuse, watery diarrhea. He denies seeing blood or mucus in the stools. On further questioning, he reveals that he eats a well-balanced diet and generally prepares his meals at home. He remembers having some shellfish from a street vendor 3 days ago. He takes no medications. His past medical history is unremarkable. Which of the following mechanisms most likely accounts for this patient’s illness?

A. Tyrosine kinase phosphorylation
B. ADP-ribosylation of Gs protein (Correct Answer)
C. Tyrosine kinase dephosphorylation
D. Osmotic effect of intestinal contents
E. Inflammation of the gastrointestinal wall

Explanation: ***ADP-ribosylation of Gs protein*** - The patient's history of consuming **shellfish from a street vendor** and presenting with **profuse, watery diarrhea** strongly suggests **cholera**. - **Cholera toxin** works by irreversibly ADP-ribosylating the **Gs alpha subunit**, leading to constitutive activation of **adenylate cyclase** and increased intracellular **cAMP**, which causes excessive fluid and electrolyte secretion into the intestinal lumen. *Tyrosine kinase phosphorylation* - This mechanism is characteristic of signaling pathways involved in growth and differentiation, often seen with **growth factor receptors**, and is not the primary cause of acute, watery diarrhea from food poisoning. - While some bacterial toxins can affect intracellular signaling, **tyrosine kinase phosphorylation** is not the direct mechanism for the massive fluid loss seen in cholera. *Tyrosine kinase dephosphorylation* - This process typically downregulates cell signaling pathways, which would likely **decrease** cellular activity, rather than trigger the profuse secretion seen in this patient's presentation. - It is not a known mechanism for the pathogenesis of infectious diarrheal diseases such as cholera. *Osmotic effect of intestinal contents* - While **osmotic diarrhea** is characterized by the presence of non-absorbable solutes in the gut lumen, drawing water in, the history here points more to an actively secreted fluid loss. - The sheer volume and rapid onset of the diarrhea suggest an active secretory mechanism rather than simply an osmotic effect from malabsorption. *Inflammation of the gastrointestinal wall* - **Inflammatory diarrhea** typically involves blood or mucus in the stool, fever, and abdominal pain, none of which are reported by the patient. - The patient's "profuse, watery" diarrhea without blood or mucus signifies a non-inflammatory, secretory etiology often caused by toxins.

Question 67: A researcher is studying a new antituberculosis drug. In the laboratory, the drug has been shown to be effective against mycobacteria located within phagolysosomes of macrophages, but it is also significantly less effective against extracellular tuberculoid bacteria. The characteristics of this drug are most similar to which of the following agents?

A. Isoniazid
B. Pyrazinamide (Correct Answer)
C. Ethambutol
D. Streptomycin
E. Rifampin

Explanation: ***Pyrazinamide*** - Pyrazinamide is unique among antituberculosis drugs for its efficacy in the **acidic environment of phagolysosomes**, where dormant mycobacteria reside. - It is **less effective against actively replicating extracellular bacteria** at neutral pH, aligning with the drug's described characteristics. *Isoniazid* - Isoniazid is primarily effective against **rapidly dividing, extracellular *M. tuberculosis*** by inhibiting mycolic acid synthesis. - While it can penetrate macrophages, its activity is not specifically enhanced or limited by the acidic phagolysosomal environment as described. *Ethambutol* - Ethambutol primarily inhibits **arabinogalactan synthesis**, affecting the cell wall of growing mycobacteria, both intracellular and extracellular. - Its efficacy is not selectively focused on the acidic intracellular environment. *Streptomycin* - Streptomycin is an **aminoglycoside antibiotic** that inhibits protein synthesis and is active against extracellular mycobacteria. - It has limited penetration into cells and is not particularly effective against intracellular organisms, nor is its activity pH-dependent. *Rifampin* - Rifampin is highly effective against both **extracellular and intracellular mycobacteria** by inhibiting DNA-dependent RNA polymerase. - It exhibits strong sterilizing activity across various environments, which contradicts the described drug's selective efficacy.

Question 68: A 44-year-old woman presents to the emergency department with a headache, vertigo, confusion, and dyspnea. A relevant history cannot be obtained from the patient because she seems confused and gives incoherent responses to questions. Her husband says that she was cleaning the kitchen this morning until the curtains caught on fire earlier this morning from the stove’s flame. Her vitals include: pulse 100/min, respirations 20/min, blood pressure 130/80 mm Hg, oxygen saturation 97% on room air. On physical examination, the patient is oriented x 0. The skin has a bright cherry-red color. Laboratory testing shows: pH 7.35 PaO2 90 mm Hg pCO2 40 mm Hg HCO3- 26 mEq/L SpO2 97% Blood lactate 11 mmol/L Which of the following is the most likely diagnosis in this patient?

A. Cyanide poisoning
B. Polycythemia
C. Carbon monoxide poisoning (Correct Answer)
D. High altitude
E. Anemia

Explanation: ***Carbon monoxide poisoning*** - The patient's presentation with **headache, vertigo, confusion, dyspnea**, and particularly the **cherry-red skin** in the context of **exposure to a kitchen fire**, is highly suggestive of **carbon monoxide (CO) poisoning**. The cherry-red skin coloration is caused by **carboxyhemoglobin** and is a classic (though not always present) sign of CO toxicity. - The **normal PaO2 (90 mm Hg)** indicates adequate oxygen dissolved in plasma, but pulse oximetry shows **falsely normal SpO2 (97%)** because standard pulse oximeters cannot differentiate between **oxyhemoglobin and carboxyhemoglobin**. This creates a false sense of adequate oxygenation. - The **elevated lactate (11 mmol/L)** results from **tissue hypoxia** as CO binds hemoglobin with 200-250 times greater affinity than oxygen, preventing oxygen delivery to tissues and causing **cellular hypoxia**. - **House fires** are the most common source of CO exposure, making this the most likely diagnosis given the clinical context. *Cyanide poisoning* - **Cyanide poisoning** can occur from smoke inhalation when synthetic materials burn and can cause confusion, dyspnea, and lactic acidosis due to **inhibition of cytochrome oxidase**, preventing cellular oxygen utilization. - However, cyanide typically causes **pink or flushed skin** rather than the classic **cherry-red color** seen with carboxyhemoglobin in CO poisoning. - While both can present with elevated lactate, the **cherry-red skin** is pathognomonic for CO, not cyanide. Additionally, cyanide poisoning would typically show **very high lactate levels** (often >15-20 mmol/L) due to complete blockade of oxidative phosphorylation. *Polycythemia* - **Polycythemia** involves an abnormally high concentration of hemoglobin, which can cause symptoms like headache and vertigo but is a **chronic condition**, not an acute presentation following fire exposure. - The **cherry-red skin** and acute confusion in the context of **smoke exposure** are not features of polycythemia. *High altitude* - **High altitude sickness** presents with headache, vertigo, and dyspnea due to **hypobaric hypoxia** causing a **decreased PaO2**, which is not seen in this patient (PaO2 is 90 mm Hg, which is normal). - The **cherry-red skin** and acute onset after a kitchen fire are completely inconsistent with high altitude sickness. *Anemia* - **Anemia** is a deficiency of red blood cells or hemoglobin leading to symptoms like fatigue, dyspnea, and **pallor** (not cherry-red skin). - The laboratory findings with **normal PaO2 and SpO2** and the acute presentation following fire exposure rule out anemia as the cause.

Question 69: A 28-year-old woman comes to the physician because of a two-month history of fatigue and low-grade fevers. Over the past 4 weeks, she has had increasing shortness of breath, a productive cough, and a 5.4-kg (11.9-lb) weight loss. Three months ago, the patient returned from a two-month trip to China. The patient appears thin. Her temperature is 37.9°C (100.2°F), pulse is 75/min, and blood pressure is 125/70 mm Hg. Examination shows lymphadenopathy of the anterior and posterior cervical chain. Rales are heard at the left lower lobe of the lung on auscultation. Laboratory studies show a leukocyte count of 11,300/mm3 and an erythrocyte sedimentation rate of 90 mm/h. An x-ray of the chest shows a patchy infiltrate in the left lower lobe and ipsilateral hilar enlargement. Microscopic examination of the sputum reveals acid-fast bacilli; polymerase chain reaction is positive. Sputum cultures are pending. After placing the patient in an airborne infection isolation room, which of the following is the most appropriate next step in management?

A. Administer only isoniazid for 9 months
B. Administer isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months, followed by isoniazid and rifampin for 4 months (Correct Answer)
C. Await culture results before initiating treatment
D. Obtain CT scan of the chest
E. Perform interferon-γ release assay

Explanation: ***Administer isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months, followed by isoniazid and rifampin for 4 months*** - This patient presents with symptoms such as **fatigue, fever, weight loss, productive cough, and shortness of breath**, along with **lymphadenopathy, rales, patchy infiltrate, ipsilateral hilar enlargement, and acid-fast bacilli in sputum**, all highly suggestive of active **pulmonary tuberculosis (TB)**. - Given the strong clinical and microbiological evidence (acid-fast bacilli, positive PCR), immediate initiation of a **four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol)** is crucial to prevent disease progression, reduce transmission, and ensure effective treatment. *Administer only isoniazid for 9 months* - **Isoniazid monotherapy** is typically used for **latent tuberculosis infection (LTBI)**, not active TB, as it is insufficient to treat active disease and carries a high risk of developing drug resistance. - The patient's symptoms, imaging findings, and positive acid-fast bacilli smear indicate **active disease**, not just latent infection. *Await culture results before initiating treatment* - Delaying treatment for active TB until **culture results** are available (which can take several weeks) is inappropriate and can lead to disease progression, increased morbidity, and higher risk of transmission to others. - The **acid-fast bacilli smear and PCR positivity** provide sufficient evidence to initiate empiric treatment immediately. *Obtain CT scan of the chest* - While a **CT scan** might provide more detailed imaging information, it is not the most immediate next step for management when active TB is strongly suspected and requires urgent treatment initiation. - The **chest x-ray findings** are already consistent with TB and sufficient to guide initial management. *Perform interferon-γ release assay* - An **interferon-γ release assay (IGRA)** is used to diagnose **latent tuberculosis infection (LTBI)**, not active TB, and does not differentiate between the two. - The patient's presentation with active symptoms, positive sputum smear, and positive PCR strongly indicates **active TB**, rendering an IGRA redundant and not helpful for determining the immediate treatment course.

Question 70: A 13-year-old girl presents with a 4-week history of unrelenting cough, night sweats, and fever. No known past medical history and no current medications. The patient recently immigrated to the country from a rural town in northern India. Vaccination status is unknown. Her temperature is 38.5°C (101.3°F), pulse is 115/min, blood pressure is 95/65 mm Hg, and respiratory rate is 22/min. Physical examination is significant for decreased breath sounds in the right upper lobe and multiple right cervical lymphadenopathies. A chest radiograph reveals multiple cavitations in the right upper lobe and right hilar lymphadenopathy. A sputum culture shows acid-fast bacilli. Which of the following compounds must be included in addition to the recommended antimicrobial therapy in this patient?

A. Thiamine
B. Folic acid
C. Riboflavin
D. Niacin
E. Pyridoxine (Correct Answer)

Explanation: ***Pyridoxine*** - This patient has **tuberculosis (TB)**, as evidenced by a 4-week history of cough, night sweats, fever, cavitary lesions, hilar lymphadenopathy, and **acid-fast bacilli** in sputum. Standard TB treatment includes **isoniazid (INH)**, which can cause **peripheral neuropathy** due to its interference with **pyridoxine (vitamin B6)** metabolism. - Supplementation with **pyridoxine** is essential for patients receiving INH to prevent this adverse effect, especially in those with risk factors like malnutrition, diabetes, or HIV. *Thiamine* - **Thiamine (vitamin B1)** deficiency is commonly associated with **alcoholism** (leading to Wernicke-Korsakoff syndrome) or malnutrition, and is not specifically indicated for prevention of side effects from standard TB treatment. - There is no specific drug in the standard anti-TB regimen that necessitates thiamine supplementation to prevent its adverse effects. *Folic acid* - **Folic acid (vitamin B9)** supplementation is crucial in conditions like **megaloblastic anemia** or during pregnancy and in patients on drugs like methotrexate. - It is not a routine supplement given with anti-TB treatment to prevent drug-induced side effects. *Riboflavin* - **Riboflavin (vitamin B2)** deficiencies can cause angular cheilitis or glossitis, but it is not specifically indicated for prevention of side effects from standard TB treatment. - No component of the typical anti-TB regimen directly interferes with riboflavin metabolism in a way that requires routine supplementation. *Niacin* - **Niacin (vitamin B3)** deficiency (pellagra) is characterized by dermatitis, diarrhea, and dementia. - It is not routinely supplemented to counteract side effects of anti-TB medications.

Question 71: A 78-year-old man receives chemotherapy for advanced hepatocellular carcinoma. Despite appropriate therapy, he dies 4 months later. Histopathological examination of the cancer cells shows the presence of a transmembrane efflux pump protein that is known to cause decreased intracellular concentrations of chemotherapeutic drugs. Which of the following best describes this membrane protein?

A. G protein
B. Cadherin
C. P-glycoprotein (Correct Answer)
D. Tyrosine receptor
E. Channel protein

Explanation: **P-glycoprotein** - **P-glycoprotein** (also known as **MDR1**) is a well-known **efflux pump** that actively transports many chemotherapy drugs out of cancer cells, leading to **multidrug resistance**. - Its presence explains the **decreased intracellular concentrations** of chemotherapy drugs and the poor response to treatment in this patient. *G protein* - **G proteins** are intracellular signaling molecules that mediate responses to various extracellular stimuli, not primarily involved in drug efflux. - They are typically associated with **G protein-coupled receptors** and downstream signaling pathways, not direct drug transport. *Cadherin* - **Cadherins** are cell adhesion molecules that play a crucial role in cell-cell binding and maintaining tissue structure. - They are not involved in the active transport of drugs across the cell membrane. *Tyrosine receptor* - **Tyrosine kinase receptors** are transmembrane proteins that bind to growth factors and initiate intracellular signaling cascades, promoting cell growth and differentiation. - They are involved in signaling, not in the active transport of chemotherapy drugs out of the cell. *Channel protein* - **Channel proteins** facilitate the passive diffusion of ions or small molecules across the cell membrane, typically down their electrochemical gradient. - While they are transmembrane proteins, they do not actively pump drugs out against a concentration gradient, which is characteristic of multidrug resistance.

Question 72: A 33-year-old woman comes to the physician for a routine health maintenance examination. She feels well. She was diagnosed with multiple sclerosis one year ago. She has had two exacerbations since then, each lasting about one week and each requiring hospitalization for corticosteroid treatment. Her most recent exacerbation was three weeks ago. In between these episodes she has had no neurologic symptoms. She takes a multivitamin and a calcium supplement daily. Her vital signs are within normal limits. Examination, including neurologic examination, shows no abnormalities. Which of the following is the most appropriate next step in pharmacotherapy?

A. Supportive therapy only as needed
B. Natalizumab
C. Mitoxantrone
D. Interferon beta (Correct Answer)
E. Methylprednisolone

Explanation: ***Interferon beta*** - This patient presents with **relapsing-remitting multiple sclerosis (RRMS)**, characterized by acute exacerbations followed by periods of full recovery, without disease progression between attacks. **Interferon beta** is a first-line disease-modifying therapy (DMT) for RRMS, reducing the frequency and severity of relapses and slowing disability progression. - Given that she has had **two exacerbations** within a year, indicating active disease not adequately controlled, initiating a DMT like interferon beta is essential for long-term management and prevention of further neurological damage. *Supportive therapy only as needed* - While supportive care is important during acute exacerbations, relying solely on it for a patient with **active RRMS** who has had multiple relapses is insufficient. - This approach fails to address the underlying disease process and will likely lead to continued relapses and long-term accumulation of disability. *Natalizumab* - **Natalizumab** is a highly effective DMT for MS, but it is typically reserved for patients with **highly active MS** or those who have failed first-line therapies due to its risk of **progressive multifocal leukoencephalopathy (PML)**. - It would not be the most appropriate *initial* pharmacotherapy for a patient whose symptoms suggest moderate activity, without prior DMT failure. *Mitoxantrone* - **Mitoxantrone** is an immunosuppressant used in **rapidly worsening MS** or secondary progressive MS, but its use is limited due to significant toxicities, including **cardiotoxicity** and risk of **secondary leukemia**. - It is generally considered a highly potent, later-line agent and not appropriate for initial management of RRMS. *Methylprednisolone* - **Methylprednisolone** (a corticosteroid) is used to treat **acute MS exacerbations** to shorten their duration and reduce symptom severity. - While she received it for her recent exacerbations, it is not a **disease-modifying therapy** for long-term management and prevention of future relapses. It addresses acute symptoms, not the underlying autoimmune process.

Question 73: A 44-year-old man, with a history of intravenous (IV) drug use, presented to the emergency department due to worsening non-productive cough, exertional dyspnea, and night sweats. His cough started 3 weeks ago and progressively worsened. He is homeless and well-known by the hospital staff. He was previously admitted to the hospital after an overdose of opioids. He takes no medication. At the hospital, the vital signs included: blood pressure 101/68 mm Hg, heart rate 99/min, respiratory rate 20/min, oxygen saturation of 91% on room air, and oral temperature of 37.4°C (99.3°F). His chest X-ray showed left perihilar shadowing. The laboratory results included: WBC count 8,800/mm3 Arterial pH 7.39 Rapid HIV testing positive with an elevated viral load PaCO2 41 mm Hg PaO2 76 mm Hg He was admitted for the treatment of presumed sepsis and pneumonia, and he was immediately started on IV ceftriaxone. An induced sputum specimen shows multiple kidney bean-shaped cysts that are approximately 5 um. These cysts stain positive with methenamine silver. What is the preferred antibiotic therapeutic regimen for this condition?

A. Intravenous liposomal amphotericin B with flucytosine
B. Isoniazid, rifabutin, pyrazinamide and ethambutol
C. Fluconazole with flucytosine
D. Trimethoprim-sulfamethoxazole (Correct Answer)
E. Clindamycin and primaquine, with adjunctive prednisone

Explanation: ***Trimethoprim-sulfamethoxazole*** - The patient's symptoms (non-productive cough, dyspnea, night sweats), history of **IV drug use**, positive **HIV** test with elevated viral load, and chest X-ray findings are highly suggestive of **Pneumocystis pneumonia (PcP)**. - The sputum analysis showing **kidney bean-shaped cysts** approximately 5 µm and staining positive with **methenamine silver** confirms PcP caused by *Pneumocystis jirovecii*. **Trimethoprim-sulfamethoxazole (TMP-SMX)** is the first-line treatment for PcP. *Intravenous liposomal amphotericin B with flucytosine* - This regimen is primarily used for severe fungal infections like **cryptococcal meningitis** or disseminated candidiasis, not *Pneumocystis jirovecii* pneumonia. - While *Pneumocystis* was once considered a fungus, it is now classified as a unique organism requiring specific antiprotozoal-like treatment, not typical antifungal agents. *Isoniazid, rifabutin, pyrazinamide and ethambutol* - This is a standard multi-drug regimen for treating **active tuberculosis (TB)**. - Although TB can cause similar pulmonary symptoms in immunocompromised patients, the sputum microscopy findings of *Pneumocystis* cysts rule out TB as the primary diagnosis requiring this specific regimen. *Fluconazole with flucytosine* - **Fluconazole** is an antifungal drug primarily used for candidiasis and cryptococcal infections, but it is **not effective** against *Pneumocystis jirovecii*. - **Flucytosine** is also an antifungal agent used in combination with amphotericin B for severe fungal infections, but it has no role in treating PcP. *Clindamycin and primaquine, with adjunctive prednisone* - This combination is an **alternative treatment regimen** for moderate to severe PcP, often used in patients who cannot tolerate TMP-SMX due to adverse effects. - While it is a valid treatment option, **TMP-SMX** remains the **preferred first-line therapy** due to its efficacy and broader availability, unless contraindications exist.

Question 74: A 15-year-old boy comes to the physician because of skin changes on his face, chest, and back over the past year. Treatment with over-the-counter benzoyl peroxide has been ineffective. Physical examination shows numerous open comedones, inflammatory papules, and pustules on his face, chest, and back. Which of the following is the most likely underlying mechanism of this patient’s skin condition?

A. Hyperkeratinization of hair follicles (Correct Answer)
B. Type IV hypersensitivity reaction
C. Formation of superficial epidermal inclusion cyst
D. Excess androgen production
E. Hyperplasia of pilosebaceous glands

Explanation: **Hyperkeratinization of hair follicles** - The primary event in the pathogenesis of **acne vulgaris** is the **shedding of hyperkeratinized corneocytes** into the lumen of the hair follicle, which then combines with sebum to form a microcomedone. - This process leads to the **obstruction of the pilosebaceous unit**, creating an anaerobic environment conducive to the proliferation of *Cutibacterium acnes* and the development of inflammatory lesions like papules and pustules. *Type IV hypersensitivity reaction* - This mechanism involves **T-cell mediated delayed hypersensitivity**, leading to conditions like **allergic contact dermatitis** or **tuberculosis**. - Acne vulgaris is not primarily an allergic reaction mediated by T cells; its pathogenesis involves follicular obstruction, sebum production, bacterial colonization, and inflammation. *Formation of superficial epidermal inclusion cyst* - Epidermal inclusion cysts (also known as epidermoid cysts) are typically solitary, slow-growing cysts that result from the **implantation of epidermal cells into the dermis**, often due to trauma or blocked hair follicles, but they are not the underlying mechanism for widespread acne. - While some severe acne lesions can rarely lead to cyst formation, the presence of numerous **comedones, papules, and pustules** indicates typical acne vulgaris, not primarily cyst formation. *Excess androgen production* - While **androgens stimulate sebum production**, which is a contributing factor to acne, they are not the initiating mechanism for the follicular obstruction itself. - Most adolescents with acne have **normal androgen levels**; the skin's sebaceous glands are simply more sensitive to circulating androgens, leading to increased sebum. *Hyperplasia of pilosebaceous glands* - **Sebaceous gland hyperplasia** refers to an increase in the number and size of sebaceous glands, leading to an overproduction of sebum, which contributes to acne. - However, the fundamental initiating event for comedone formation in acne is the **follicular hyperkeratinization and obstruction**, rather than simply the glands being hyperplastic.

Question 75: A 4-year-old girl is brought to the emergency department by her father for the evaluation of abdominal pain for 1 hour after drinking a bottle of rust remover. The father reports that she vomited once on the way to the hospital and that her vomit was not bloody. The patient has pain with swallowing. She appears uncomfortable. Oral examination shows mild erythema of the epiglottis and heavy salivation. Which of the following is the most likely long-term complication in this patient?

A. Esophageal strictures (Correct Answer)
B. Esophageal webs
C. Mallory-Weiss tears
D. Thyroglossal fistula
E. Oral cavity cancer

Explanation: ***Esophageal strictures*** - Ingestion of corrosive substances like **rust remover** (typically acidic) causes **severe chemical burns** to the esophagus, leading to inflammation and tissue damage. - Over time, as the damaged esophageal tissue heals, it can form **fibrotic scar tissue**, resulting in the narrowing of the esophageal lumen, known as strictures, which can lead to dysphagia. *Esophageal webs* - Esophageal webs are **thin, eccentric mucosal folds** that protrude into the esophageal lumen, often congenital or associated with iron deficiency anemia (Plummer-Vinson syndrome). - While they can cause dysphagia, they are **not typically a direct complication of acute caustic ingestion**. *Mallory-Weiss tears* - These are **longitudinal mucosal tears** at the gastroesophageal junction, usually caused by forceful vomiting, which can lead to **upper gastrointestinal bleeding**. - Although the patient vomited, it was not bloody, and Mallory-Weiss tears are an **acute complication** rather than a long-term structural sequela of corrosive ingestion. *Thyroglossal fistula* - A thyroglossal fistula is a **persistently open tract** that results from the incomplete obliteration of the thyroglossal duct during embryonic development. - This is a **congenital anomaly** unrelated to caustic ingestion and typically presents as a neck mass or drainage from the anterior neck. *Oral cavity cancer* - While long-term exposure to certain carcinogens can increase the risk of oral cancers, a single acute ingestion of a caustic substance is **not typically a direct cause** of oral cavity cancer. - The immediate and most common long-term complication from such an event is esophageal damage.

Question 76: A 7-month-old girl is brought to the pediatrician by her parents with a mild, persistent fever for the past week. The patient’s mother also states she is feeding poorly and has become somewhat lethargic. The patient was born at term and the delivery was uncomplicated. The child’s birth weight was 3.5 kg (7.7 lb) and at 6 months was 7.0 kg (15.4 lb). She is fully immunized. The patient’s father recently returned from a business trip to India with a mild cough and was diagnosed with tuberculosis. The patient’s mother tests negative for tuberculosis The patient’s temperature is 38.1℃ (100.5℉). Today, she weighs 7.0 kg (15.4 lb). Cardiopulmonary auscultation reveals diminished breath sounds in the upper lobes. A chest radiograph demonstrates hilar lymphadenopathy and infiltrates in the upper lobes. Gastric aspirates are positive for acid-fast bacilli, however, cultures are still pending. Father and daughter are both started on standard antitubercular therapy. Which of the following is the appropriate management for the patient’s mother?

A. Isoniazid and rifampicin
B. Isoniazid alone (Correct Answer)
C. No medication is required
D. Isoniazid, rifampicin, and pyrazinamide
E. Isoniazid, rifampicin, pyrazinamide, and ethambutol

Explanation: ***Isoniazid alone*** - The mother is a **close household contact** to TWO active tuberculosis cases (her husband and daughter), placing her at extremely high risk for TB infection. - Although her TB test is currently **negative**, she may be in the **window period** (8-10 weeks post-exposure before test conversion) or at ongoing risk of infection. - **Preventive therapy with isoniazid** (daily for 9 months or twice-weekly for 9 months) is recommended by CDC guidelines for high-risk contacts, even with negative initial testing, to prevent development of active TB. - She should undergo **repeat TB testing in 8-10 weeks** to detect delayed conversion. *Isoniazid and rifampicin* - This combination (3-4 months duration) is an **alternative regimen for LTBI treatment**, shorter than isoniazid monotherapy. - However, for contacts with **negative testing**, single-drug prophylaxis with isoniazid is the standard first-line recommendation. - This regimen would be appropriate if she had **documented LTBI** (positive test) and needed a shorter course. *No medication is required* - This would be **inappropriate** given her extremely high-risk exposure to two household members with active TB. - Even with negative testing, household contacts warrant preventive therapy due to the risk of recent infection in the window period and ongoing exposure. - Failure to provide prophylaxis could result in progression to active TB. *Isoniazid, rifampicin, and pyrazinamide* - This three-drug regimen is used for the **intensive phase of active TB treatment**, not for preventive therapy in contacts. - The mother has **no evidence of active disease** (negative test, asymptomatic), so this would be overtreatment with unnecessary toxicity risk. *Isoniazid, rifampicin, pyrazinamide, and ethambutol* - This four-drug regimen is the standard for treating **active tuberculosis** or when drug resistance is suspected. - This represents significant **overtreatment** for a contact with negative testing and no clinical evidence of disease. - Would expose her to unnecessary adverse effects including hepatotoxicity and optic neuritis.

Question 77: A 42-year-old man with non-small cell lung cancer is enrolled in a clinical trial for a new chemotherapeutic drug. The drug prevents microtubule depolymerization by binding to the beta subunit of tubulin. The mechanism of action of this new drug is most similar to which of the following?

A. Bleomycin
B. Irinotecan
C. Vincristine
D. Cladribine
E. Paclitaxel (Correct Answer)

Explanation: ***Paclitaxel*** - **Paclitaxel** is a **taxane** that stabilizes microtubules by binding to the **beta-tubulin subunit**, preventing their depolymerization and arresting cells in metaphase. - This mechanism is consistent with the described drug's action of preventing **microtubule depolymerization**. *Bleomycin* - **Bleomycin** is an **antitumor antibiotic** that causes **DNA strand breaks** by forming free radicals. - Its mechanism is entirely different from microtubule stabilization. *Irinotecan* - **Irinotecan** is a **topoisomerase I inhibitor** that prevents DNA unwinding, leading to DNA damage and cell death. - This drug targets DNA replication and repair, not microtubule dynamics. *Vincristine* - **Vincristine** is a **vinca alkaloid** that inhibits microtubule formation by binding to **beta-tubulin**, preventing its polymerization (assembly). - While it also targets microtubules, its action is to *prevent polymerization*, whereas the new drug prevents *depolymerization*. *Cladribine* - **Cladribine** is a **purine analog** that inhibits DNA synthesis by incorporating into DNA and RNA, leading to strand breaks and cell death. - This drug primarily interferes with nucleic acid metabolism, not microtubule function.

Question 78: A 33-year-old Hispanic woman who recently immigrated to the United States with her newborn daughter is presenting to a free clinic for a wellness checkup for her baby. As part of screening for those immigrating or seeking refuge in the United States, she and her child are both evaluated for tuberculosis. The child’s purified protein derivative (PPD) test and chest radiograph are negative, and although the mother’s chest radiograph is also negative, her PPD is positive. She states that she is currently asymptomatic and has no known history of tuberculosis (TB). The mother’s vital signs include: blood pressure 124/76 mm Hg, heart rate 74/min, and respiratory rate 14/min. She is advised to begin treatment with isoniazid, supplemented with pyridoxine for the next 9 months. She asks about the potential for harm to the child if she begins this course of treatment since she is breastfeeding. Which of the following is the most appropriate response to this patient’s concerns?

A. “You should not breastfeed your baby for the next 9 months because isoniazid in breast milk can damage your child’s liver.”
B. “You should not breastfeed your baby for the next 9 months because pyridoxine in breast milk can damage your child’s liver.”
C. “You may breastfeed your baby because you are asymptomatic and because neither isoniazid nor pyridoxine will harm your child.” (Correct Answer)
D. “You should not breastfeed your baby because she is at greater risk for infection with TB than for adverse side effects of your treatment regimen.”
E. “You may breastfeed your baby because pyridoxine will prevent isoniazid from causing peripheral neuropathy.”

Explanation: ***“You may breastfeed your baby because you are asymptomatic and because neither isoniazid nor pyridoxine will harm your child.”*** - The **benefits of breastfeeding** (providing immunity, nutrition, and bonding) generally outweigh the minimal risks associated with isoniazid and pyridoxine secretion into breast milk. - Since the mother is **asymptomatic** and her chest X-ray is negative, she has **latent tuberculosis infection (LTBI)**, making transmission to the infant highly unlikely through casual contact, and therefore breastfeeding is safe. *“You should not breastfeed your baby for the next 9 months because isoniazid in breast milk can damage your child’s liver.”* - While **isoniazid (INH)** can cause drug-induced hepatitis in adults, the amount excreted in breast milk is typically very low and **not considered harmful** to the infant's liver. - The American Academy of Pediatrics states that INH is **compatible with breastfeeding**. *“You should not breastfeed your baby for the next 9 months because pyridoxine in breast milk can damage your child’s liver.”* - **Pyridoxine (vitamin B6)** is a vitamin and is added to the treatment regimen to **prevent INH-induced peripheral neuropathy**; it is not harmful to the infant's liver and is naturally present in breast milk. - There is **no evidence** that pyridoxine in breast milk can cause liver damage in an infant. *“You should not breastfeed your baby because she is at greater risk for infection with TB than for adverse side effects of your treatment regimen.”* - The mother has **latent TB**, not active TB, meaning she is **not contagious** and cannot spread the infection to her infant. - Breastfeeding does not increase the risk of TB transmission from a mother with LTBI, and preventing transmission is best achieved through treating the mother's LTBI. *“You may breastfeed your baby because pyridoxine will prevent isoniazid from causing peripheral neuropathy.”* - This statement accurately describes a function of **pyridoxine** for the mother (preventing **peripheral neuropathy**), but it does not address the infant's safety concerning breast milk intake. - While correct that pyridoxine prevents this side effect in the mother, it's not the primary reason why breastfeeding is safe for the infant.

Question 79: A 54-year-old woman presents with acute pain in her left toe. She says she hasn't been able to wear closed shoes for 2 weeks. Past medical history is significant for gastroesophageal reflux disease, diagnosed 2 years ago. The patient is afebrile and vital signs are within normal limits. Her BMI is 31 kg/m2. On physical examination, the left toe is warm to touch, swollen, and erythematous. A joint fluid aspiration from the left toe is performed and shows needle-shaped negatively birefringent urate crystals. The patient is started on methotrexate for gout prophylaxis. On her follow-up visit 6 weeks later, she has an elevated homocysteine level, a decreased serum folic acid level, and a normal methylmalonic acid level. Which of the following drugs would most likely cause a similar side effect to that seen in this patient?

A. Cisplatin
B. α-Methyldopa
C. Cephalosporins
D. Penicillins
E. Azathioprine (Correct Answer)

Explanation: ***Azathioprine*** - Both methotrexate and azathioprine are **antimetabolites** that cause **myelosuppression** by interfering with nucleic acid synthesis in rapidly dividing cells - Methotrexate inhibits dihydrofolate reductase, blocking folate metabolism essential for purine and thymidine synthesis, leading to **folate deficiency** (elevated homocysteine, low folate) - Azathioprine, a purine analog, inhibits purine synthesis and can cause similar **bone marrow suppression**, though through a different mechanism - Both agents share common toxicities including leukopenia, thrombocytopenia, and increased infection risk *Cisplatin* - Cisplatin is a **platinum-based alkylating agent** that cross-links DNA strands - Primary toxicities are **nephrotoxicity**, ototoxicity, and peripheral neuropathy—not related to folate metabolism or antimetabolite effects *α-Methyldopa* - Alpha-methyldopa is a **centrally-acting antihypertensive** (alpha-2 agonist) used especially in pregnancy - Side effects include sedation, orthostatic hypotension, and hemolytic anemia—**not myelosuppression or folate-related effects** *Cephalosporins* - Cephalosporins are **beta-lactam antibiotics** that inhibit bacterial cell wall synthesis - Well-tolerated with main side effects being **gastrointestinal upset and hypersensitivity reactions**—no antimetabolite effects *Penicillins* - Penicillins are **beta-lactam antibiotics** with similar mechanism to cephalosporins - Primary concern is **hypersensitivity reactions** (rash to anaphylaxis)—no antimetabolite or bone marrow suppression effects

Question 80: A 22-year-old female with a history of bipolar disease presents to the emergency room following an attempted suicide. She reports that she swallowed a bottle of pain reliever pills she found in the medicine cabinet five hours ago. She currently reports malaise, nausea, and anorexia. She has vomited several times. Her history is also notable for alcohol abuse. Her temperature is 99.4°F (37.4°C), blood pressure is 140/90 mmHg, pulse is 90/min, and respirations are 20/min. Physical examination reveals a pale, diaphoretic female in distress with mild right upper quadrant tenderness to palpation. Liver function tests and coagulation studies are shown below: Serum: Alkaline phosphatase: 110 U/L Aspartate aminotransferase (AST, GOT): 612 U/L Alanine aminotransferase (ALT, GPT): 557 U/L Bilirubin, Total: 2.7 mg/dl Bilirubin, Direct: 1.5 mg/dl Prothrombin time: 21.7 seconds Partial thromboplastin time (activated): 31 seconds International normalized ratio: 2.0 Serum and urine drug levels are pending. Which of the following medications should be administered to this patient?

A. Atropine
B. Flumazenil
C. Fomepizole
D. Physostigmine
E. N-acetylcysteine (Correct Answer)

Explanation: ***N-acetylcysteine*** - The patient's symptoms (malaise, nausea, anorexia, vomiting, RUQ tenderness), elevated transaminases (AST, ALT), hyperbilirubinemia, and coagulopathy (elevated PT/INR) following a pain reliever overdose strongly suggest **acetaminophen toxicity**. - **N-acetylcysteine (NAC)** is the antidote for acetaminophen overdose, working by replenishing **glutathione** stores and detoxifying the toxic metabolite **NAPQI**, preventing further hepatic damage. *Atropine* - **Atropine** is an anticholinergic medication used to treat bradycardia or organophosphate poisoning. - The patient's symptoms and vital signs are not consistent with cholinergic toxicity. *Flumazenil* - **Flumazenil** is a benzodiazepine receptor antagonist used to reverse the effects of **benzodiazepine overdose**. - There is no clinical indication for benzodiazepine overdose in this patient presentation. *Fomepizole* - **Fomepizole** is an alcohol dehydrogenase inhibitor used as an antidote for **methanol** or **ethylene glycol** poisoning. - While the patient has a history of alcohol abuse, her current presentation and lab findings are not consistent with methanol or ethylene glycol toxicity. *Physostigmine* - **Physostigmine** is a **cholinesterase inhibitor** used to treat anticholinergic toxicity. - The patient's symptoms and vital signs are not indicative of anticholinergic poisoning.

Question 81: A 67-year-old woman presents to the infectious disease clinic after her PPD was found to be positive. A subsequent chest radiography shows a cavity in the apex of the right upper lobe, along with significant hilar adenopathy. The patient is diagnosed with tuberculosis and is started on the standard four-drug treatment regimen. Four weeks later, she returns for her first follow-up appointment in panic because her eyes have taken on an orange/red hue. Which of the following describes the mechanism of action of the drug most likely responsible for this side effect?

A. Inhibition of RNA polymerase (Correct Answer)
B. Inhibition of squalene epoxidase
C. Inhibition of arabinosyltransferase
D. Inhibition of mycolic acid synthesis
E. Inhibition of topoisomerase

Explanation: ***Inhibition of RNA polymerase*** - The drug most likely responsible for the **orange/red discoloration of tears, sweat, saliva, and urine is rifampin**. - **Rifampin exerts its bactericidal effect by inhibiting bacterial DNA-dependent RNA polymerase**, thereby blocking RNA synthesis. *Inhibition of squalene epoxidase* - This mechanism of action is characteristic of **terbinafine**, an antifungal drug. - **Terbinafine is used to treat fungal infections** like dermatophytosis and onychomycosis, not tuberculosis. *Inhibition of arabinosyltransferase* - This is the **mechanism of action for ethambutol**, another first-line drug for tuberculosis. - While ethambutol is part of the standard regimen, its primary side effect is **optic neuritis**, not orange discoloration of bodily fluids. *Inhibition of mycolic acid synthesis* - This mechanism is primarily associated with **isoniazid (INH)**, a key drug in tuberculosis treatment. - **Isoniazid's main toxicities include hepatotoxicity and peripheral neuropathy**, not the red-orange discoloration. *Inhibition of topoisomerase* - This mechanism is characteristic of **fluoroquinolone antibiotics**, such as ciprofloxacin and levofloxacin. - While fluoroquinolones can be used in some tuberculosis regimens, they are typically **second-line agents** and do not cause the orange/red bodily fluid discoloration.

Question 82: A 60-year-old man comes to the physician because of persistent fatigue over the past ten months. His previous annual health maintenance examination showed no abnormalities. He appears pale. Physical examination shows numerous petechial lesions over the abdomen and marked splenomegaly. His serum hemoglobin concentration is 9.4 g/dL, leukocyte count is 4,100/mm3, and thrombocyte count is 110,000/mm3. A peripheral blood smear shows large white blood cells with centrally placed nuclei and multiple fine, radial cytoplasmic projections that stain positively for tartrate-resistant acid phosphatase (TRAP). Which of the following is the most likely characteristic of the medication used as first-line treatment for this patient's condition?

A. Increases risk of thromboembolic events
B. Inhibits progression from G2 phase
C. Unable to cross the blood-brain barrier
D. Resistant to breakdown by adenosine deaminase (Correct Answer)
E. Requires bioactivation by the liver

Explanation: ***Resistant to breakdown by adenosine deaminase*** - The patient's presentation with **fatigue**, **pale appearance**, **petechiae**, **splenomegaly**, **pancytopenia**, and characteristic **"hairy cells"** (large leukocytes with fine, radial cytoplasmic projections that stain **TRAP-positive**) is highly indicative of **hairy cell leukemia (HCL)**. - The first-line treatment for HCL involves purine analogs like **cladribine** or **pentostatin**. These drugs are **resistant to breakdown by adenosine deaminase (ADA)**, allowing them to accumulate in lymphoid cells and induce apoptosis. *Increases risk of thromboembolic events* - While some cancer treatments can increase the risk of thromboembolic events, purine analogs like cladribine and pentostatin are **not primarily known for this side effect**. - **Thromboembolic events** are more commonly associated with certain chemotherapies (e.g., thalidomide, lenalidomide) or direct effects of some cancers. *Inhibits progression from G2 phase* - This statement describes the mechanism of action of **microtubule inhibitors** (e.g., taxanes, vinca alkaloids) which arrest cells in the **M phase** or **G2/M phase** of the cell cycle. - **Purine analogs** like cladribine and pentostatin are **cytotoxic during the S phase** by interfering with DNA synthesis and repair, not typically by arresting G2 phase progression. *Unable to cross the blood-brain barrier* - While many chemotherapy drugs have difficulty crossing the **blood-brain barrier (BBB)**, **cladribine (2-CdA)**, which is a common first-line agent for HCL, **does penetrate the central nervous system (CNS)**. - This characteristic can be relevant in certain CNS lymphomas or leukemias, but it's not the defining feature of HCL treatment. *Requires bioactivation by the liver* - **Purine analogs** like cladribine and pentostatin are **intracellularly phosphorylated** to their active triphosphate forms by **kinases** within the target cells. - This activation is **not primarily hepatic bioactivation** but rather occurs within the lymphoid cells themselves, where they interfere with DNA metabolism.

Question 83: A 2-year-old girl is rushed to the emergency department by her parents following ingestion of unknown pills from an unmarked bottle she found at the park. The parents are not sure how many pills she ingested but say the child has been short of breath since then. Her respiratory rate is 50/min and pulse is 150/min. Examination shows the girl to be quite restless and agitated. No other findings are elicited. Laboratory testing shows: Serum electrolytes Sodium 142 mEq/L Potassium 4.0 mEq/L Chloride 105 mEq/L Bicarbonate 14 mEq/L Serum pH 7.23 The girl most likely ingested which of the following drugs?

A. Spironolactone
B. Calcium carbonate
C. Codeine
D. Salicylates/Aspirin (Correct Answer)
E. Acetaminophen

Explanation: ***Salicylates/Aspirin*** - This presentation is **classic for salicylate (aspirin) poisoning** in a child. Salicylates cause **direct stimulation of the respiratory center**, leading to **tachypnea** and respiratory alkalosis initially, but also cause **uncoupling of oxidative phosphorylation**, resulting in **high anion gap metabolic acidosis**. - The anion gap here is **elevated at 23 mEq/L** (142 - (105 + 14) = 23; normal is 8-12), consistent with salicylate toxicity. - In **pediatric patients**, the metabolic acidosis component often **predominates** and may present without preceding respiratory alkalosis, unlike adults who typically show mixed acid-base disturbances. - Clinical features include **tachycardia, tachypnea, agitation, restlessness**, hyperthermia, tinnitus, and altered mental status - matching this patient's presentation. - Treatment involves activated charcoal (if early), alkaline diuresis with sodium bicarbonate, and hemodialysis for severe cases. *Acetaminophen* - Acetaminophen overdose does **NOT** cause acute metabolic acidosis, tachypnea, or tachycardia immediately after ingestion. - The **first 24 hours** after acetaminophen ingestion are typically **asymptomatic** or show only mild nausea and vomiting. - **Metabolic acidosis with elevated lactate** occurs only in **late-stage toxicity** (48-72 hours post-ingestion) when severe **hepatic failure** develops, not acutely as presented here. - This patient's immediate symptoms after ingestion rule out acetaminophen as the culprit. *Spironolactone* - Spironolactone is a **potassium-sparing diuretic** that can cause **hyperkalemia** and **non-anion gap (hyperchloremic) metabolic acidosis**. - This patient has a **high anion gap** metabolic acidosis, which is inconsistent with spironolactone toxicity. - Overdose would cause **dehydration, hypotension**, and electrolyte disturbances, not the acute agitation and tachypnea seen here. *Calcium carbonate* - Calcium carbonate causes **metabolic alkalosis** (milk-alkali syndrome), not metabolic acidosis. - Would present with hypercalcemia symptoms: confusion, constipation, polyuria, and renal insufficiency. - Does not cause tachypnea, tachycardia, or the acid-base disturbance seen in this case. *Codeine* - Codeine is an **opioid** causing **CNS and respiratory depression**. - Classic opioid toxidrome: **miosis, bradypnea, decreased respiratory rate**, and sedation - the opposite of this presentation. - Would not cause tachypnea, tachycardia, agitation, or metabolic acidosis.

Question 84: A 55-year-old woman with diabetes presents to the emergency department due to swelling of her left leg, fever, and chills for the past 2 days. The woman’s maximum recorded temperature at home was 38.3°C (101.0°F). Her left leg is red and swollen from her ankle to the calf, with an ill-defined edge. Her vital signs include: blood pressure 120/78 mm Hg, pulse rate 94/min, temperature 38.3°C (101.0°F), and respiratory rate 16/min. On physical examination, her left leg shows marked tenderness and warmth compared with her right leg. The left inguinal lymph node is enlarged to 3 x 3 cm. Which of the following chemical mediators is the most likely cause of the woman’s fever?

A. Bradykinin
B. Histamine
C. PGE2 (Correct Answer)
D. Arachidonic acid
E. LTB4

Explanation: ***PGE2*** - **Prostaglandin E2 (PGE2)** is a potent **pyrogen** that acts on the **hypothalamus** to reset the body's thermoregulatory set point, leading to fever. - In infections like **cellulitis**, inflammatory mediators stimulate the production of PGE2, causing the systemic symptom of fever. *Bradykinin* - **Bradykinin** primarily mediates **pain** and **vasodilation** at the site of inflammation. - While it contributes to local signs of inflammation, it is not a direct mediator of systemic fever. *Histamine* - **Histamine** is a key mediator in immediate **hypersensitivity reactions** and local inflammation, causing **vasodilation** and increased **vascular permeability**. - It does not directly induce fever by acting on the thermoregulatory center. *Arachidonic acid* - **Arachidonic acid** is a **precursor** molecule derived from membrane phospholipids, which is metabolized to various inflammatory mediators like prostaglandins and leukotrienes. - It is not a direct chemical mediator of fever itself; rather, its downstream products such as PGE2 are. *LTB4* - **Leukotriene B4 (LTB4)** is a potent **chemotactic agent** for neutrophils, playing a role in immune cell recruitment to the site of inflammation. - While involved in inflammation, LTB4 does not directly cause fever.

Question 85: An American pediatrician travels to Bangladesh on a medical mission. While working in the local hospital's emergency room, she sees a 2-week-old boy who was brought in by his mother with muscle spasms and difficulty sucking. The mother gave birth at home at 38 weeks gestation and was attended to by her older sister who has no training in midwifery. The mother had no prenatal care. She has no past medical history and takes no medications. The family lives on a small fishing vessel on a major river, which also serves as their fresh water supply. The boy's temperature is 99°F (37.2°C), blood pressure is 100/60 mmHg, pulse is 130/min, and respirations are 22/min. On exam, the boy's arms are flexed at the elbow, his knees are extended, and his neck and spine are hyperextended. Tone is increased in the bilateral upper and lower extremities. He demonstrates sustained facial muscle spasms throughout the examination. The umbilical stump is foul-smelling. Cultures are taken, and the appropriate treatment is started. This patient's condition is most likely caused by a toxin with which of the following functions?

A. Binding to MHC II and the T cell receptor simultaneously
B. Blocking voltage-gated sodium channel opening
C. Blocking release of GABA and glycine (Correct Answer)
D. Blocking voltage-gated calcium channel opening
E. Blocking release of acetylcholine

Explanation: ***Blocking release of GABA and glycine*** - The clinical presentation of muscle spasms, hyperextension (opisthotonus), difficulty sucking, and a foul-smelling umbilical stump in a neonate born at home in a developing country strongly suggests **neonatal tetanus**. - **Tetanus toxin (tetanospasmin)**, produced by *Clostridium tetani*, acts by preventing the release of inhibitory neurotransmitters **GABA** and **glycine** from Renshaw cells in the spinal cord, leading to uncontrolled muscle contractions and spasms. *Binding to MHC II and the T cell receptor simultaneously* - This describes the action of **superantigens**, such as **toxic shock syndrome toxin-1 (TSST-1)** from *Staphylococcus aureus* or streptococcal pyrogenic exotoxins. - Superantigens cause widespread T cell activation and cytokine release, leading to symptoms like fever, rash, and shock, which are not the primary symptoms here. *Blocking voltage-gated sodium channel opening* - Toxins that block voltage-gated sodium channels, such as **tetrodotoxin** (from pufferfish) and **saxitoxin** (from shellfish), interfere with nerve impulse propagation. - This typically results in **paralysis** and numbness, rather than the sustained muscle spasms seen in this patient. *Blocking voltage-gated calcium channel opening* - Blocking voltage-gated calcium channels can impair neurotransmitter release at the presynaptic terminal, leading to **muscle weakness** or paralysis. - Examples include toxins like **conotoxins** (from cone snails) or certain autoimmune conditions attacking these channels (e.g., Lambert-Eaton myasthenic syndrome), which do not fit the spastic presentation described. *Blocking release of acetylcholine* - This is the mechanism of **botulinum toxin**, produced by *Clostridium botulinum*, which blocks the release of **acetylcholine** at the neuromuscular junction. - This leads to **flaccid paralysis**, not the spastic paralysis and sustained muscle contractions observed in the patient.

Question 86: A 55-year-old male presents to his primary care physician for a normal check-up. He has a history of atrial fibrillation for which he takes metoprolol and warfarin. During his last check-up, his international normalized ratio (INR) was 2.5. He reports that he recently traveled to Mexico for a business trip where he developed a painful red rash on his leg. He was subsequently prescribed an unknown medication by a local physician. The rash resolved after a few days and he currently feels well. His temperature is 98.6°F (37°C), blood pressure is 130/80 mmHg, pulse is 95/min, and respirations are 18/min. Laboratory analysis reveals that his current INR is 4.5. Which of the following is the most likely medication this patient took while in Mexico?

A. Griseofulvin
B. Rifampin
C. St. John’s wort
D. Trimethoprim-sulfamethoxazole (Correct Answer)
E. Phenobarbital

Explanation: ***Trimethoprim-sulfamethoxazole*** - **Trimethoprim-sulfamethoxazole** is a potent inhibitor of **CYP2C9**, the primary enzyme responsible for metabolizing **warfarin**, leading to significantly increased INR and bleeding risk. - The patient's **elevated INR (4.5)** from a previous stable level of 2.5 strongly suggests an interaction with a medication that inhibits warfarin metabolism, and trimethoprim-sulfamethoxazole is a common culprit. - TMP-SMX is commonly used to treat **cellulitis** and other skin infections, which aligns with the clinical presentation of a painful red rash. *Griseofulvin* - **Griseofulvin** is an antifungal agent that acts as a **CYP inducer**, which would *increase* warfarin metabolism and lead to a *decreased* INR, not the elevated INR seen in this patient. - While it could treat fungal skin infections (e.g., tinea), it would cause the opposite effect on warfarin levels. *Rifampin* - **Rifampin** is a strong **CYP inducer**, meaning it would *increase* warfarin metabolism and thus *decrease* INR, leading to a higher risk of clotting, which is the opposite of what is seen in this patient. - It is often used for tuberculosis or serious bacterial infections, not typically for a simple skin rash. *St. John's wort* - **St. John's wort** is a known **CYP inducer**, similar to rifampin, and would lead to a *decrease* in warfarin levels and INR. - It is an herbal supplement primarily used for depression and would not typically be prescribed by a physician for a rash. *Phenobarbital* - **Phenobarbital** is a potent **CYP inducer**, which would *accelerate* warfarin metabolism and result in a *decreased* INR, increasing the risk of thrombosis. - It is an anticonvulsant and sedative, not a medication typically prescribed for a rash.

Question 87: A 17-year-old girl is brought to the emergency department 6 hours after she attempted suicide by consuming 16 tablets of acetaminophen (500 mg per tablet). At present, she does not have any complaints or symptoms. The patient is afebrile and vital signs are within normal limits. Physical examination is unremarkable. Laboratory findings show a serum acetaminophen level that is predictive of ‘probable hepatic toxicity’ on the Rumack-Matthew nomogram. Treatment is started with a drug, which is a precursor of glutathione and is a specific antidote for acetaminophen poisoning. Which of the following is an additional beneficial mechanism of action of this drug in this patient?

A. Promotes glucuronidation of unmetabolized acetaminophen
B. Promotes microcirculatory blood flow (Correct Answer)
C. Promotes fecal excretion of unabsorbed acetaminophen
D. Prevents gastrointestinal absorption of acetaminophen
E. Promotes oxidation of N-acetyl-p-benzoquinoneimine (NAPQI)

Explanation: ***Promotes microcirculatory blood flow*** - **N-acetylcysteine** (NAC), the antidote for acetaminophen poisoning, acts as a **vasodilator** and **improves microcirculatory blood flow**, which can be beneficial in preventing and treating liver injury. - This benefit is particularly relevant in cases of severe poisoning, where compromised hepatic perfusion can exacerbate damage. *Promotes glucuronidation of unmetabolized acetaminophen* - NAC primarily works by replenishing **glutathione stores**, which are crucial for detoxifying the toxic metabolite **NAPQI**, not by enhancing glucuronidation. - Glucuronidation is a separate metabolic pathway that conjugates acetaminophen for excretion and is not directly augmented by NAC. *Promotes fecal excretion of unabsorbed acetaminophen* - NAC is given systemically (orally or intravenously) to counteract absorbed acetaminophen and does not directly promote fecal excretion of unabsorbed drug. - Activated charcoal is used to prevent absorption if given shortly after ingestion. *Prevents gastrointestinal absorption of acetaminophen* - NAC does not prevent the **Gastrointestinal absorption** of acetaminophen; it is administered after absorption has occurred and the drug is circulating in the body. - Measures like activated charcoal or gastric lavage are used to prevent absorption if the patient presents early enough. *Promotes oxidation of N-acetyl-p-benzoquinoneimine (NAPQI)* - NAC works by **reducing** the toxic metabolite **NAPQI** back to acetaminophen and by replenishing **glutathione**, which then detoxifies NAPQI. - It does not promote the *oxidation* of NAPQI; rather, it facilitates its *reduction* or conjugation to render it harmless.

Question 88: A 32-year-old woman is admitted to the hospital after undergoing an open cholecystectomy under general anesthesia. Preoperatively, the patient was administered a single dose of intravenous ceftriaxone. Now, the anesthetic effects have worn off, and her pain is well managed. The patient has a prior medical history of hypertension which has been well-controlled by captopril for 2 years. Her vitals currently show: blood pressure 134/82 mm Hg, heart rate 84/min, and respiratory rate 16/min. Postoperative laboratory findings are significant for the following: Serum glucose (random) 174 mg/dL Serum electrolytes Sodium 142 mEq/L Potassium 3.9 mEq/L Chloride 101 mEq/L Serum creatinine 0.9 mg/dL Blood urea nitrogen 10 mg/dL Alanine aminotransferase (ALT) 150 U/L Aspartate aminotransferase (AST) 172 U/L Serum bilirubin (total) 0.9 mg/dL Preoperative labs were all within normal limits. Which of the following drugs is most likely responsible for this patient’s abnormal laboratory findings?

A. Captopril
B. Propofol
C. Nitrous oxide
D. Sevoflurane (Correct Answer)
E. Ceftriaxone

Explanation: ***Sevoflurane*** - **Sevoflurane** is a volatile halogenated anesthetic that can rarely cause **postoperative hepatotoxicity** (halogenated anesthetic hepatitis) - This presents with **elevated transaminases** (ALT and AST) within 2-14 days post-surgery - Sevoflurane can also cause **transient hyperglycemia** through stress response and insulin resistance during and after anesthesia - While less hepatotoxic than halothane, sevoflurane metabolism produces trifluoroacetic acid derivatives that can trigger immune-mediated liver injury in susceptible individuals - Renal function remains normal, distinguishing this from fluoride-induced nephrotoxicity *Captopril* - **Captopril** is an ACE inhibitor that can rarely cause **cholestatic hepatitis** with chronic use - However, the patient has been on captopril for 2 years with normal preoperative labs, making it an unlikely cause of acute postoperative transaminase elevation - Does not explain the hyperglycemia observed *Propofol* - **Propofol** is an intravenous anesthetic that can cause **propofol infusion syndrome** with prolonged high-dose infusions (typically >48 hours) - While propofol can cause metabolic derangements, acute transaminase elevation is not a typical feature of short-term use for routine surgery - The degree of liver enzyme elevation seen here is more consistent with volatile anesthetic hepatotoxicity *Nitrous oxide* - **Nitrous oxide** inactivates **vitamin B12** (methionine synthase inhibition), leading to megaloblastic anemia and neurological complications with prolonged or repeated exposure - Does not cause acute hepatotoxicity or explain the elevated transaminases and glucose seen in this case *Ceftriaxone* - **Ceftriaxone** can cause **cholestatic hepatitis** and hyperbilirubinemia, particularly with prolonged use - However, this patient received only a **single preoperative dose**, making ceftriaxone an unlikely cause - The patient's bilirubin is normal (0.9 mg/dL), which would be elevated in ceftriaxone-induced cholestasis - Does not explain the hyperglycemia

Question 89: A 13-year-old girl is brought to the physician because of an itchy rash on her knee and elbow creases. She has had this rash since early childhood. Physical examination of the affected skin shows crusty erythematous papules with skin thickening. She is prescribed topical pimecrolimus. The beneficial effect of this drug is best explained by inhibition of which of the following processes?

A. Synthesis of tetrahydrofolic acid
B. Oxidation of inosine-5-monophosphate
C. Reduction of ribonucleotides
D. Oxidation of dihydroorotic acid
E. Calcineurin phosphatase activity (Correct Answer)

Explanation: ***Calcineurin phosphatase activity*** - Pimecrolimus is a **calcineurin inhibitor**, which works by blocking the phosphatase activity of calcineurin, an intracellular protein involved in T-cell activation. - Inhibiting calcineurin prevents the **dephosphorylation of NFAT (Nuclear Factor of Activated T-cells)**, thus impairing its translocation to the nucleus and subsequent transcription of pro-inflammatory cytokines like IL-2. *Synthesis of tetrahydrofolic acid* - Inhibition of **tetrahydrofolic acid synthesis** is the mechanism of action for drugs like **methotrexate** and **trimethoprim**, which interfere with folate metabolism. - These drugs are primarily used in chemotherapy or for bacterial infections, not directly for atopic dermatitis via calcineurin inhibition. *Oxidation of inosine-5-monophosphate* - The enzyme **inosine-5'-monophosphate dehydrogenase (IMPDH)** is involved in the de novo synthesis of guanine nucleotides. - Drugs like **mycophenolate mofetil** inhibit IMPDH, primarily used as immunosuppressants in transplant medicine and autoimmune diseases, not the primary mechanism for pimecrolimus. *Reduction of ribonucleotides* - The enzyme **ribonucleotide reductase** converts ribonucleotides to deoxyribonucleotides, a crucial step in DNA synthesis. - Hydroxyurea, for example, inhibits this enzyme, which is used in conditions like myeloproliferative disorders, not the mechanism of pimecrolimus. *Oxidation of dihydroorotic acid* - The enzyme **dihydroorotate dehydrogenase (DHODH)** is involved in the de novo pyrimidine synthesis pathway. - **Leflunomide** inhibits DHODH, an action used in the treatment of rheumatoid arthritis, which is distinct from the mechanism of action of pimecrolimus.

Question 90: A 57-year-old man comes to the emergency department because of pain in the sides of his abdomen and blood-tinged urine since the previous night. Over the last 2 days, he has also had progressive malaise, myalgia, and a generalized itchy rash. He has a history of gastroesophageal reflux that did not respond to ranitidine but has improved since taking pantoprazole 2 months ago. He occasionally takes acetaminophen for back pain. His vital signs are within normal limits. Examination shows a generalized, diffuse maculopapular rash. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 13 g/dL Leukocyte count 7,800/mm3 Serum Na+ 140 mEq/L Cl- 105 mEq/L K+ 4.6 mEq/L HCO3- 25 mEq/L Glucose 102 mg/dL Creatinine 4.1 mg/dL Renal ultrasonography shows no abnormalities. Which of the following findings is most likely to be observed in this patient?

A. Elevated levels of eosinophils in urine (Correct Answer)
B. Mesangial IgA deposits on renal biopsy
C. Urinary crystals on brightfield microscopy
D. Crescent-shape extracapillary cell proliferation
E. Papillary calcifications on CT imaging

Explanation: ***Elevated levels of eosinophils in urine*** - This patient's symptoms of **fever, rash, eosinophilia (implied by high creatinine and drug history), and acute kidney injury** after starting pantoprazole strongly suggest **acute interstitial nephritis (AIN)**. **Eosinophiluria** is a hallmark of AIN. - The history of recent initiation of **pantoprazole**, a proton pump inhibitor, is a significant clue as it is a common cause of drug-induced AIN. *Mesangial IgA deposits on renal biopsy* - **IgA nephropathy** typically presents with recurrent gross hematuria, often triggered by an upper respiratory infection. - It would not explain the prominent **maculopapular rash**, malaise, and myalgia, which are more characteristic of a drug reaction. *Urinary crystals on brightfield microscopy* - **Urinary crystals** are associated with conditions like nephrolithiasis or certain drug toxicities, but not typically with this constellation of symptoms including a rash and systemic malaise. - While the patient has flank pain and hematuria, the **acute kidney injury (creatinine 4.1 mg/dL)** and rash are inconsistent with simple crystaluria. *Crescent-shape extracapillary cell proliferation* - This finding is characteristic of **rapidly progressive glomerulonephritis (RPGN)**, which presents with severe acute renal failure and nephritic syndrome. - While the patient has acute kidney injury, the prominent **rash, malaise, and eosinophilia** in the context of drug exposure point away from RPGN as the primary diagnosis. *Papillary calcifications on CT imaging* - **Papillary calcifications** or **nephrocalcinosis** indicate calcium deposition in the kidney parenchyma, often seen in chronic conditions like hyperparathyroidism or renal tubular acidosis. - This imaging finding is not consistent with the acute presentation of systemic symptoms (rash, malaise) and acute kidney injury in this patient.

Question 91: A 57-year-old patient comes to the physician for a 2-month history of progressive dyspnea and cough productive of large amounts of yellow, blood-tinged sputum. He has a history of COPD and recurrent upper respiratory tract infections. Examination of the lung shows bilateral crackles and end-expiratory wheezing. An x-ray of the chest shows thin-walled cysts and tram-track opacities in both lungs. The physician prescribes nebulized N-acetylcysteine. Which of the following is the most likely effect of this drug?

A. Increase of ciliary beat rate
B. Inhibition of peptidoglycan crosslinking
C. Inhibition of phosphodiesterase
D. Breakdown of leukocyte DNA
E. Breaking of disulfide bonds (Correct Answer)

Explanation: ***Breaking of disulfide bonds*** - **N-acetylcysteine** is a **mucolytic** agent that works by cleaving the **disulfide bonds** in mucin glycoproteins, thereby reducing the viscosity of sputum. - This action helps to thin thick secretions, making them easier to clear from the airways, which is beneficial in conditions like **bronchiectasis** (suggested by the 'tram-track opacities' and 'thin-walled cysts' on X-ray, along with large amounts of sputum). *Increase of ciliary beat rate* - This is primarily enhanced by **beta-agonists** or **methylxanthines**, not N-acetylcysteine. - While improved mucociliary clearance is a goal, N-acetylcysteine achieves it by altering mucus properties, not directly by increasing ciliary activity. *Inhibition of peptidoglycan crosslinking* - This is the mechanism of action for **beta-lactam antibiotics** (e.g., penicillins, cephalosporins), which target bacterial cell walls. - N-acetylcysteine has no antibacterial properties or effects on bacterial cell wall synthesis. *Inhibition of phosphodiesterase* - **Phosphodiesterase inhibitors** (e.g., theophylline, roflumilast) work by increasing intracellular **cAMP** levels, leading to bronchodilation and anti-inflammatory effects. - This is not the mechanism by which N-acetylcysteine exerts its therapeutic effect. *Breakdown of leukocyte DNA* - This is the mechanism of action of **dornase alfa** (recombinant human deoxyribonuclease I), which is used in cystic fibrosis to break down DNA released from neutrophils in thick mucus. - N-acetylcysteine acts on mucin proteins, not DNA.

Question 92: A 42-year-old man presents to a free dermatology clinic, complaining of itchy skin over the past several days. He has no insurance and lives in a homeless shelter. The patient has no significant medical history. Physical evaluation reveals 2 mm erythematous papules and vesicles on his back and groin, with linear excoriation marks. Careful observation of his hands reveals serpiginous, grayish, threadlike elevations in the superficial epidermis, ranging from 3–9 mm in length in the webbing between several digits. What should be the suggested treatment in this case?

A. No medication should be administered, only proper hygiene.
B. Antiviral medication
C. Permethrin (Correct Answer)
D. Antifungal medication
E. Broad-spectrum antibiotic

Explanation: ***Permethrin*** - This patient's symptoms, including intense itching, erythematous papules and vesicles, linear excoriations, and especially the **serpiginous, grayish, threadlike elevations (burrows)** in the web spaces of the fingers, are classic signs of **scabies**. - **Permethrin cream** (5%) is the first-line treatment for scabies due to its high efficacy and safety profile, targeting the *Sarcoptes scabiei* mite. *No medication should be administered, only proper hygiene.* - While good hygiene is important for overall health, it is **insufficient** to eradicate a parasitic infestation like scabies. - Scabies requires **specific pharmacologic intervention** to kill the mites and eggs, as they are not simply washed away. *Antiviral medication* - **Antiviral medications** are used to treat viral infections (e.g., herpes, varicella), which do not present with the characteristic burrows or respond to antiviral agents. - The patient's symptoms are indicative of a **parasitic infestation**, not a viral one. *Antifungal medication* - **Antifungal medications** are indicated for fungal infections (e.g., ringworm, candidiasis), which typically present with a different morphology (e.g., annular lesions with raised borders) and lack the classic burrows seen in scabies. - The clinical presentation points away from a fungal etiology. *Broad-spectrum antibiotic* - **Broad-spectrum antibiotics** treat bacterial infections. While secondary bacterial infections can occur due to scratching in scabies, the primary issue here is the mite infestation itself, which antibiotics do not address. - Treating the primary scabies infestation is crucial to stop the itching and prevent further secondary infections.

Question 93: A 22-year-old man presents with abdominal cramps and diarrhea over the last few weeks. He notes that several of his bowel movements have a small amount of blood. Past medical history is significant for an intermittent cough that has been persistent since returning from Mexico last month. The patient takes no current medications. On physical examination, there is diffuse tenderness to palpation. Which of the following medications is indicated for this patient’s condition?

A. Pyrantel
B. Praziquantel
C. Albendazole
D. Mebendazole
E. Ivermectin (Correct Answer)

Explanation: ***Ivermectin*** - This patient's symptoms (abdominal cramps, bloody diarrhea, persistent cough, recent travel to Mexico) are highly suggestive of **Strongyloidiasis**. **Ivermectin** is the drug of choice for this parasitic infection. - Strongyloidiasis larvae can cause a **transient cough** as they migrate through the lungs, and adult worms in the intestines lead to gastrointestinal symptoms like **diarrhea** and abdominal pain. *Pyrantel* - **Pyrantel** is primarily effective against **pinworms**, **roundworms**, and **hookworms**, but not Strongyloides. - It works by neuromuscular blockade, causing paralysis and expulsion of the worms. *Praziquantel* - **Praziquantel** is the drug of choice for treating **tapeworm** infections (e.g., Taenia species) and **schistosomiasis**. - It acts by increasing the permeability of the worm's cells to calcium, leading to paralysis and death. *Albendazole* - **Albendazole** is a broad-spectrum anthelmintic effective against many intestinal nematodes, including **hookworm**, **roundworm**, and **whipworm**, and some tissue nematodes. - While it has some activity against Strongyloides, **Ivermectin is generally preferred** due to higher efficacy and fewer side effects in many cases of strongyloidiasis. *Mebendazole* - **Mebendazole** is effective against various intestinal worms such as **pinworms**, **roundworms**, and **hookworms**. - Its mechanism of action involves inhibiting microtubule synthesis, thereby impairing glucose uptake by the worms.

Question 94: A 38-year-old woman is diagnosed with a stage IIIa infiltrating ductal carcinoma involving the left breast. The tumor is ER/PR positive, HER-2 negative, poorly differentiated Bloom-Richardson grade 3. 4/20 regional nodes are positive. The patient undergoes a lumpectomy with axillary lymph node dissection, followed by chemotherapy and radiation therapy to the left breast and axilla. Her chemotherapy regimen involves doxorubicin, cyclophosphamide, and paclitaxel. Following completion of the intensive phase, she is started on tamoxifen as an adjuvant therapy. 6 months later, she presents with increasing fatigue, orthopnea, and paroxysmal nocturnal dyspnea. Physical examination reveals the presence of an S3 gallop, jugular venous distension (JVD), pedal edema, and ascites. She is diagnosed with congestive cardiac failure and admitted for further management. An echocardiogram confirms the diagnosis of dilated cardiomyopathy with severe systolic dysfunction and an ejection fraction of 10%. Her medical history prior to the diagnosis of breast cancer is negative for any cardiac conditions. The baseline echocardiogram prior to starting chemotherapy and a 12-lead electrocardiogram were normal. Which of the following is most likely responsible for her current cardiac condition?

A. Cyclophosphamide
B. Radiation therapy
C. Myocarditis
D. Doxorubicin (Correct Answer)
E. Tamoxifen

Explanation: ***Doxorubicin*** - **Doxorubicin** is a well-known anthracycline chemotherapy agent with a dose-dependent and cumulative cardiotoxic effect, often leading to **dilated cardiomyopathy** and congestive heart failure. - The patient's presentation with **severe heart failure** symptoms and a dramatic drop in ejection fraction after chemotherapy strongly implicates doxorubicin as the cause. *Cyclophosphamide* - While **cyclophosphamide** can cause cardiac toxicity, particularly at high doses, it more commonly manifests as **myocarditis** or pericarditis rather than chronic dilated cardiomyopathy with severe systolic dysfunction as described. - The cardiotoxicity of cyclophosphamide is generally less common and less severe than that of doxorubicin in typical breast cancer chemotherapy regimens. *Radiation therapy* - **Radiation therapy** to the chest can cause cardiac damage, including **pericarditis**, accelerated atherosclerosis, and restrictive cardiomyopathy. - However, the timeframe for significant radiation-induced cardiomyopathy leading to such severe dilated heart failure is typically much longer, often years after treatment, not 6 months. *Myocarditis* - **Myocarditis** can cause heart failure, but it is typically an **inflammatory process** of the myocardium, often triggered by viral infections, and is usually an acute rather than a cumulative, treatment-induced effect in this context. - While some chemotherapies can cause myocarditis, the clinical picture of a delayed, progressive cardiomyopathy with significantly reduced ejection fraction after specific cardiotoxic drugs points away from acute myocarditis as the primary cause. *Tamoxifen* - **Tamoxifen**, an antiestrogen used in ER/PR positive breast cancer, is generally not associated with significant **cardiotoxicity** or dilated cardiomyopathy. - Its main cardiovascular side effects are usually related to an increased risk of **thromboembolic events**, not direct myocardial damage leading to heart failure.

Question 95: A 56-year-old man comes to the physician for a follow-up examination. Two weeks ago, he was treated for an acute gout attack of the metatarsophalangeal joints of his right big toe. His symptoms improved with naproxen. He has had three other similar episodes of joint pain in his toes and ankles during the last year that improved with over-the-counter analgesics. He does not currently take any medications. He used to drink 3–5 beers daily but has recently cut down. He is a chef at a steakhouse. His temperature is 37.0°C (98.6°F), pulse is 76/min, and blood pressure is 147/83 mm Hg. Examination of his right big toe shows minimal tenderness; there is no warmth or apparent deformity. The remainder of the examination shows no abnormalities. His serum creatinine concentration is 0.9 mg/dL. Long-term treatment with which of the following drugs is most appropriate to prevent future gout attacks?

A. Pegloticase
B. Aspirin
C. Allopurinol (Correct Answer)
D. Colchicine
E. Probenecid

Explanation: ***Allopurinol*** - This patient has a history of recurrent gout attacks (four episodes in the last year), indicating the need for **long-term urate-lowering therapy**. - **Allopurinol** is a **xanthine oxidase inhibitor** that reduces uric acid production, making it the first-line urate-lowering agent for preventing future gout attacks. *Pegloticase* - This drug is reserved for patients with **severe, refractory chronic gout** who have failed other urate-lowering therapies or have significant tophi. - Its mechanism involves converting uric acid to allantoin, which is then excreted, but it carries risks of **infusion reactions** and **anaphylaxis**. *Aspirin* - **Low-dose aspirin** can actually **elevate uric acid levels** by inhibiting tubular uric acid secretion, potentially worsening gout. - While it has anti-inflammatory properties at higher doses, it is not used for chronic gout prevention due to its hyperuricemic effect and risk of GI side effects. *Colchicine* - **Colchicine** is effective for the **acute treatment of gout flares** and as a prophylactic agent to prevent flares during the initiation of urate-lowering therapy. - However, it does not lower uric acid levels and is not a long-term monotherapy for preventing gout attacks in patients with recurrent episodes. *Probenecid* - **Probenecid** is a **uricosuric agent** that increases renal excretion of uric acid. - It is typically used as a second-line agent in patients with underexcretion of uric acid and normal renal function, or as an add-on to allopurinol if target uric acid levels are not met. This patient's creatinine is normal, but allopurinol is preferred as first line.

Question 96: A 67-year-old woman who was recently diagnosed with Crohn disease comes to the physician for evaluation of her immunosuppressive therapy. She has had recurrent flares since her diagnosis. Physical examination shows two shallow ulcers on her oral mucosa. The physician considers adding azathioprine to her medication regimen. A deficiency of which of the following enzymes would diminish the therapeutic effect of this drug?

A. Phosphoribosyl pyrophosphate synthetase
B. Dihydrofolate reductase
C. Thymidylate synthase
D. Xanthine oxidase
E. Hypoxanthine-guanine phosphoribosyl transferase (Correct Answer)

Explanation: ***Hypoxanthine-guanine phosphoribosyl transferase*** - **Azathioprine** is a prodrug converted to **6-mercaptopurine (6-MP)**, which is then activated to **thioguanine nucleotides** (active metabolites) via the purine salvage pathway. - **Hypoxanthine-guanine phosphoribosyl transferase (HGPRT)** is essential for converting 6-MP into its active thiopurine metabolites that inhibit purine synthesis and suppress the immune system. - A deficiency in **HGPRT** (as seen in **Lesch-Nyhan syndrome**) would lead to reduced formation of active drug metabolites, thereby **diminishing therapeutic efficacy** in treating Crohn disease. *Phosphoribosyl pyrophosphate synthetase* - This enzyme synthesizes **phosphoribosyl pyrophosphate (PRPP)**, a precursor for de novo **purine and pyrimidine synthesis**. - While important for nucleotide metabolism, a deficiency would not directly reduce the activation of azathioprine through the salvage pathway. *Dihydrofolate reductase* - **Dihydrofolate reductase (DHFR)** is the target of **methotrexate**, which blocks the reduction of dihydrofolate to tetrahydrofolate, inhibiting DNA synthesis. - It is not involved in the metabolism or activation of azathioprine. *Thymidylate synthase* - **Thymidylate synthase** converts deoxyuridylate to deoxythymidylate, a critical step in DNA synthesis. - This enzyme is targeted by drugs like **5-fluorouracil (5-FU)** but is not related to azathioprine's mechanism of action. *Xanthine oxidase* - **Xanthine oxidase** catabolizes azathioprine and 6-MP into **inactive metabolites**, thereby **reducing drug levels and toxicity**. - **Inhibition** of xanthine oxidase (e.g., by **allopurinol**) increases active thiopurine metabolites, enhancing both therapeutic effect and toxicity risk. - Xanthine oxidase deficiency would **increase** rather than diminish therapeutic effect.

Question 97: A 75 year-old gentleman presents to the primary care physician with a 2 week history of right sided achilles tendon pain. He states that the pain has had a gradual onset and continues to worsen, now affecting the left side for the past 2 days. He denies any inciting event. Of note the patient performs self-catheterization for episodes of urinary retention and has been treated on multiple occasions for recurrent urinary tract infections. What is the most important next step in management for this patient's achilles tendon pain?

A. Switch medication and avoid exercise (Correct Answer)
B. Perform MRI
C. Refer patient to an orthopedic surgeon
D. Place permanent urinary catheter
E. Perform CT scan

Explanation: ***Switch medication and avoid exercise*** - This patient is likely experiencing **fluoroquinolone-induced tendinopathy**, a known side effect of this class of antibiotics. Given his history of recurrent UTIs and self-catheterization, he is likely on or has recently been on fluoroquinolones. - The most crucial step is to **discontinue the offending drug** (fluoroquinolone) and advise **rest/avoidance of exercise** to prevent tendon rupture, especially of the Achilles tendon. *Perform MRI* - While an MRI could confirm tendinopathy, it is **not the most important *initial* step in management**. The clinical picture strongly suggests drug-induced tendinopathy, making medication cessation more urgent. - Delaying medication change to await imaging results could **increase the risk of tendon rupture**. *Refer patient to an orthopedic surgeon* - Referral to an orthopedic surgeon might be necessary if the tendinopathy progresses to a **rupture** or if conservative measures fail. - However, the immediate and most critical action is to **address the likely cause** by discontinuing the suspected medication, not immediately involving surgery. *Place permanent urinary catheter* - While appropriate management of urinary retention is important, placing a permanent catheter is **not directly related to the acute management of Achilles tendon pain** and does not address the likely drug-induced cause. - This is a long-term management decision for his urological condition and **not the priority** for his tendon issue. *Perform CT scan* - A CT scan has **limited utility** for diagnosing tendon pathology, as it is less effective than MRI for soft tissue visualization. - It would expose the patient to **unnecessary radiation** without providing significant diagnostic benefit for tendinopathy.

Question 98: A 32-year-old woman, gravida 2, para 1, at 20 weeks' gestation comes to the physician for a prenatal visit. She feels well. Her first pregnancy was uncomplicated and the child was delivered vaginally. Medications include folic acid and an iron supplement. Her temperature is 37°C (98.6°F), pulse is 98/min, respirations are 18/min, and blood pressure is 108/76 mm Hg. Abdominal examination shows a uterus that is consistent with a 20-week gestation. The second-trimester scan shows no abnormalities. The patient intends to travel next month to Mozambique to visit her grandmother. Which of the following drugs is most suitable for pre-exposure prophylaxis against malaria?

A. Mefloquine (Correct Answer)
B. Primaquine
C. Chloroquine
D. Doxycycline
E. Proguanil

Explanation: ***Mefloquine*** - **Mefloquine** is the **most appropriate antimalarial prophylaxis** for pregnant women traveling to **chloroquine-resistant areas** such as Mozambique, particularly after the first trimester. - Mozambique has **widespread chloroquine-resistant *P. falciparum* malaria**, making mefloquine the preferred choice according to CDC and WHO guidelines. - While mefloquine is avoided in the first trimester due to limited safety data, it is considered **safe in the second and third trimesters** of pregnancy. - Though neuropsychiatric side effects can occur, the benefits outweigh risks when traveling to high-risk malaria areas during pregnancy. *Primaquine* - **Primaquine** is *contraindicated* in pregnancy because it can cause **hemolytic anemia** in the fetus if the fetus has **glucose-6-phosphate dehydrogenase (G6PD) deficiency**. - It is used primarily for the **radical cure** of *P. vivax* and *P. ovale* malaria (to eradicate liver hypnozoites), not as a primary prophylactic agent. *Chloroquine* - While **chloroquine** is safe in pregnancy and preferred for **chloroquine-sensitive malaria** areas, it is *not appropriate for Mozambique*. - Mozambique has **high rates of chloroquine-resistant *P. falciparum* malaria**, making chloroquine ineffective for prophylaxis in this region. - Chloroquine would only be suitable for travel to areas with confirmed chloroquine-sensitive malaria (e.g., Central America west of Panama Canal, parts of the Middle East). *Doxycycline* - **Doxycycline** is *contraindicated* in pregnancy and in children under eight years old due to its potential to cause **permanent dental discoloration**, **enamel hypoplasia**, and inhibition of **bone growth** in the developing fetus. *Proguanil* - **Atovaquone-proguanil** (Malarone) has limited safety data in pregnancy and is generally not recommended as a first-line option when other proven alternatives are available. - While some data suggest it may be safe, **mefloquine** is preferred for chloroquine-resistant areas during pregnancy due to more extensive safety documentation in the second and third trimesters.

Question 99: A 54-year-old woman presents for follow-up care for her type 2 diabetes mellitus. She was diagnosed approximately 2 years ago and was treated with dietary modifications, an exercise regimen, metformin, and glipizide. She reports that her increased thirst and urinary frequency has not improved with her current treatment regimen. Her hemoglobin A1c is 8.5% at this visit. She is started on a medication that will result in weight loss but places her at increased risk of developing urinary tract infections and vulvovaginal candidiasis. Which of the following is the mechanism of action of the prescribed medication?

A. Peroxisome proliferator-activated receptor activator
B. Glucagon-like protein-1 receptor agonist
C. Sodium-glucose co-transporter-2 inhibitor (Correct Answer)
D. Alpha-glucosidase inhibitor
E. Dipeptidyl peptidase-4 inhibitor

Explanation: ***Sodium-glucose co-transporter-2 inhibitor*** - The patient's **HbA1c of 8.5%** indicates uncontrolled diabetes, and the mention of weight loss and increased risk of **urinary tract infections (UTIs)** and **vulvovaginal candidiasis** strongly points to an SGLT2 inhibitor. - SGLT2 inhibitors work by **blocking glucose reabsorption in the renal tubules**, leading to increased glucose excretion in urine, which can cause candidiasis and UTIs, and also contributes to weight loss. *Peroxisome proliferator-activated receptor activator* - This refers to **thiazolidinediones (TZDs)**, which reduce insulin resistance by increasing glucose uptake in peripheral tissues, but are not associated with increased UTIs or vulvovaginal candidiasis. - TZDs can cause **weight gain** and fluid retention, which is contrary to the weight loss mentioned in the stem. *Glucagon-like protein-1 receptor agonist* - GLP-1 receptor agonists like liraglutide and semaglutide encourage **weight loss** and improve glycemic control by increasing insulin secretion and decreasing glucagon secretion, but they are not primarily associated with increased risk of UTIs or candidiasis. - Their common side effects include **gastrointestinal issues** such as nausea and vomiting. *Alpha-glucosidase inhibitor* - These medications (e.g., acarbose) work by **delaying carbohydrate absorption** in the gut, which primarily helps reduce postprandial glucose levels. - They commonly cause **gastrointestinal side effects** such as flatulence and diarrhea, and are not associated with UTIs, candidiasis, or significant weight loss. *Dipeptidyl peptidase-4 inhibitor* - DPP-4 inhibitors (e.g., sitagliptin, saxagliptin) enhance the effects of incretin hormones by **preventing their breakdown**, leading to increased insulin secretion and decreased glucagon. - They are generally **weight-neutral** and do not cause the specific adverse effects (UTIs, candidiasis) mentioned in the clinical scenario.

Question 100: A 68-year-old woman comes to the physician for evaluation of diminished vision for several months. Twenty-eight years ago, she was diagnosed with systemic lupus erythematosus, which has been well controlled with hydroxychloroquine. Fundoscopic examination shows concentric rings of hypopigmentation and hyperpigmentation surrounding the fovea bilaterally. Visual field examination of this patient is most likely to show which of the following findings?

A. Right monocular blindness
B. Bitemporal hemianopia
C. Paracentral scotoma (Correct Answer)
D. Homonymous hemianopia
E. Binasal hemianopia

Explanation: ***Paracentral scotoma*** - The fundoscopic findings of **concentric rings of hypopigmentation and hyperpigmentation surrounding the fovea** (bull's-eye maculopathy) are characteristic of **hydroxychloroquine toxicity**. - **Hydroxychloroquine toxicity** typically causes a **paracentral scotoma**, meaning loss of vision in an area adjacent to the central point of vision. *Right monocular blindness* - This would indicate a problem with the **right optic nerve** or the right eye itself, affecting all vision in that eye. - It is not a typical finding for **hydroxychloroquine retinopathy**, which primarily affects the macula. *Bitemporal hemianopia* - This visual field defect is characterized by loss of vision in the **outer (temporal) halves of both visual fields**. - It is typically caused by compression of the **optic chiasm**, often by a **pituitary tumor**, not by retinal toxicity from hydroxychloroquine. *Homonymous hemianopia* - This involves loss of vision in the **same half of the visual field in both eyes** (e.g., losing the right half of vision in both eyes). - This defect indicates a lesion **posterior to the optic chiasm** (e.g., in the optic tract, lateral geniculate nucleus, optic radiations, or visual cortex). *Binasal hemianopia* - This involves loss of vision in the **inner (nasal) halves of both visual fields**. - This rare defect can be caused by lesions compressing the **uncrossed nasal fibers** of both optic nerves, usually due to bilateral internal carotid artery aneurysms.

Question 101: A 55-year-old woman presents to the physician because of a fever 4 days after discharge from the hospital following induction chemotherapy for acute myeloid leukemia (AML). She has no other complaints and feels well otherwise. Other than the recent diagnosis of AML, she has no history of a serious illness. The temperature is 38.8°C (101.8°F), the blood pressure is 110/65 mm Hg, the pulse is 82/min, and the respirations are 14/min. Examination of the catheter site, skin, head and neck, heart, lungs, abdomen, and perirectal area shows no abnormalities. The results of the laboratory studies show: Hemoglobin 9 g/dL Leukocyte count 800/mm3 Percent segmented neutrophils 40% Platelet count 85,000/mm3 Which of the following is the most appropriate pharmacotherapy at this time?

A. Valacyclovir
B. Vancomycin
C. Imipenem (Correct Answer)
D. Caspofungin
E. Ciprofloxacin

Explanation: ***Imipenem*** - This patient presents with **febrile neutropenia** (fever >38.3°C and absolute neutrophil count <500/mm³ or expected to fall below 500/mm³). This is a **medical emergency** requiring prompt empiric **broad-spectrum antibiotic** therapy covering **Gram-positive** and **Gram-negative** organisms. - **Imipenem** is a carbapenem antibiotic with broad-spectrum activity, making it an appropriate choice for empiric treatment of febrile neutropenia, especially in high-risk patients like those undergoing induction chemotherapy for AML. *Valacyclovir* - **Valacyclovir** is an antiviral medication used primarily for **herpes simplex** and **varicella-zoster virus** infections. - While immunocompromised patients are susceptible to viral infections, there is no clinical evidence at this time to suggest a viral etiology, and **febrile neutropenia** takes precedence for immediate broad-spectrum antibacterial coverage. *Vancomycin* - **Vancomycin** is an antibiotic that specifically targets **Gram-positive bacteria**, particularly **methicillin-resistant Staphylococcus aureus (MRSA)**. - Empiric vancomycin is not typically recommended as initial sole therapy for febrile neutropenia unless there is strong suspicion of a Gram-positive infection (e.g., catheter-related infection, mucositis, skin and soft tissue infection, or known colonization with MRSA), which is not present here. *Caspofungin* - **Caspofungin** is an **antifungal** medication used to treat invasive fungal infections, including candidiasis and aspergillosis. - Initial management of febrile neutropenia focuses on bacterial infections; empiric antifungal therapy is usually initiated if fever persists despite broad-spectrum antibiotics for several days. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic with good activity against many **Gram-negative bacteria** but limited activity against **Gram-positive organisms** and anaerobes. - While it can be used for prophylaxis or as part of a combination regimen, it is not considered sufficient as a single agent for empiric treatment of **high-risk febrile neutropenia** due to its limited spectrum and increasing resistance patterns.

Question 102: A 31-year-old male traveler in Thailand experiences fever, headache, and excessive sweating every 48 hours. Peripheral blood smear shows trophozoites and schizonts indicative of Plasmodia infection. The patient is given chloroquine and primaquine. Primaquine targets which of the following Plasmodia forms:

A. Schizont
B. Hypnozoite (Correct Answer)
C. Trophozoite
D. Merozoite
E. Sporozoite

Explanation: ***Hypnozoite*** - **Primaquine** is a **radical cure** for malaria caused by *Plasmodium vivax* and *Plasmodium ovale* because it targets the dormant **hypnozoite** forms in the liver. - The presence of **hypnozoites** leads to relapses, as they can reactivate and re-initiate the erythrocytic cycle. *Schizont* - **Schizonts** are merozoite-producing forms in red blood cells (**erythrocytic schizonts**) or liver cells (**hepatic schizonts**). - While chloroquine targets **erythrocytic schizonts**, primaquine's primary unique action is against the dormant liver stages. *Trophozoite* - **Trophozoites** are the feeding and growing stages of the parasite within red blood cells, which mature into schizonts. - **Chloroquine** is highly effective against **erythrocytic trophozoites** and schizonts, resolving acute malarial symptoms. *Merozoite* - **Merozoites** are released from ruptured schizonts and infect new red blood cells during the erythrocytic cycle. - No specific antimalarial drug solely targets **merozoites** as a primary form; they are an infective stage for red blood cells. *Sporozoite* - **Sporozoites** are the forms injected by infected mosquitoes, which then travel to the liver and infect hepatocytes. - While some drugs like atovaquone have activity against sporozoites, primaquine is specifically indicated for destroying the **hypnozoite** stage, preventing relapses.

Question 103: A 71-year-old man with colon cancer presents to his oncologist because he has been experiencing photosensitivity with his current chemotherapeutic regimen. During the conversation, they decide that his symptoms are most likely a side effect of the 5-fluorouracil he is currently taking and decide to replace it with another agent. The patient is curious why some organs appear to be especially resistant to chemotherapy whereas others are particularly susceptible to chemotherapy. Which of the following cell types would be most resistant to chemotherapeutic agents?

A. Cardiac myocytes (Correct Answer)
B. Hematopoietic cells
C. Liver hepatocytes
D. Enterocytes
E. Hair follicle cells

Explanation: ***Cardiac myocytes*** - **Cardiac myocytes** are highly differentiated, **terminally differentiated cells** that rarely divide, making them inherently resistant to chemotherapeutic agents which primarily target rapidly dividing cells. - Their **low mitotic activity** means they are less susceptible to agents that interfere with DNA replication, cell division, or other cell cycle-dependent processes. *Hematopoietic cells* - **Hematopoietic cells** in the bone marrow are among the most **rapidly dividing cells** in the body, making them extremely susceptible to chemotherapy. - Damage to these cells leads to **myelosuppression**, a common and serious side effect of chemotherapy. *Liver hepatocytes* - **Hepatocytes** have a **moderate proliferative capacity**, allowing for regeneration, but they are still more susceptible to chemotherapy than terminally differentiated cells. - While they can regenerate, they are particularly vulnerable to hepatotoxic chemotherapy agents due to their role in **drug metabolism** and detoxification. *Enterocytes* - **Enterocytes** of the small intestine lining have a **very high turnover rate**, making them highly sensitive to chemotherapeutic agents. - This sensitivity explains common side effects like **mucositis**, diarrhea, and nausea due to damage to the intestinal lining. *Hair follicle cells* - **Hair follicle cells** are also characterized by their rapid division and high metabolic activity, which makes them very vulnerable to chemotherapy. - Damage to these cells leads to **alopecia** (hair loss), a well-known side effect of many chemotherapeutic regimens.

Question 104: A 20-year-old man presents with a tremor involving his upper limbs for the past 3 weeks. He says his symptoms have been progressively worsening. Past medical history is significant for 2 episodes of undiagnosed jaundice over the last year. No significant family history. His temperature is 36.9°C (98.4°F), the pulse is 82/min, the blood pressure is 116/78 mm Hg, and the respiratory rate is 12/min. On physical examination, there is excessive salivation, and he has an expressionless face. He has an ataxic gait accompanied by asymmetric resting and kinetic tremors. Hepatomegaly is evident. There is a greenish-gold limbal ring in both corneas. After laboratory findings confirm the diagnosis, the patient is prescribed a medication that he is warned may worsen his tremors. The patient is also instructed to return in a week for a complete blood count and urinalysis. Which of the following additional adverse effects may be expected in this patient while taking this medication?

A. Weight gain
B. Pulmonary fibrosis
C. Myasthenia gravis (Correct Answer)
D. Constipation
E. Sensorineural deafness

Explanation: ***Myasthenia gravis*** - This patient's symptoms (tremor, excessive salivation, expressionless face, ataxic gait, hepatomegaly, greenish-gold limbal rings) are highly suggestive of **Wilson's disease**, a disorder of copper metabolism. The described medication is likely **D-penicillamine**, a copper-chelating agent used to treat Wilson's Disease. - **D-penicillamine** is associated with various adverse effects, including autoimmune conditions such as drug-induced **myasthenia gravis**, characterized by muscle weakness. *Weight gain* - **Weight gain** is not a typical adverse effect of D-penicillamine. - While D-penicillamine can cause gastrointestinal issues, it is not commonly linked to significant changes in weight. *Pulmonary fibrosis* - **Pulmonary fibrosis** is a rare but serious adverse effect associated with D-penicillamine, but it is less common than autoimmune reactions. - Other medications, such as amiodarone or methotrexate, are more commonly associated with drug-induced pulmonary fibrosis. *Constipation* - **Constipation** is not a commonly reported adverse effect of D-penicillamine. - Gastrointestinal side effects like nausea, vomiting, and diarrhea are more typical. *Sensorineural deafness* - **Sensorineural deafness** is not a known adverse effect of D-penicillamine. - Ototoxicity leading to hearing loss is more commonly associated with medications like aminoglycoside antibiotics or platinum-based chemotherapeutics.

Question 105: A 55-year-old man, who was recently diagnosed with tuberculosis, presents to his primary care provider as part of his routine follow-up visit every month. He is currently in the initial phase of anti-tubercular therapy. His personal and medical histories are relevant for multiple trips to Southeast Asia as part of volunteer activities and diabetes of 5 years duration, respectively. A physical examination is unremarkable except for a visual abnormality on a color chart; he is unable to differentiate red from green. The physician suspects the visual irregularity as a sign of toxicity due to one of the drugs in the treatment regimen. Which of the following is the mechanism by which this medication acts in the treatment of Mycobacterium tuberculosis?

A. Inhibition of DNA-dependent RNA polymerase
B. Inhibition of arabinosyltransferase (Correct Answer)
C. Inhibition of protein synthesis by binding to the 30S ribosomal subunit
D. Inhibition of mycolic acid synthesis
E. Induction of free radical metabolites

Explanation: ***Inhibition of arabinosyltransferase*** - The patient's inability to differentiate red from green is a classic symptom of **optic neuritis** (specifically retrobulbar neuritis), a known side effect of **ethambutol**. - **Ethambutol** works by inhibiting **arabinosyltransferase**, an enzyme essential for the synthesis of the mycobacterial cell wall component **arabinogalactan**. *Inhibition of DNA-dependent RNA polymerase* - This is the mechanism of action for **rifampin**, another first-line anti-TB drug. - While rifampin has various side effects (e.g., **hepatotoxicity**, **red-orange discoloration of bodily fluids**), **optic neuritis** is not its primary or common adverse effect. *Inhibition of protein synthesis by binding to the 30S ribosomal subunit* - This mechanism is characteristic of **aminoglycosides** (e.g., streptomycin, amikacin) and **tetracyclines**, which are used in certain TB regimens, especially for **drug-resistant cases**. - Common side effects include **ototoxicity** and **nephrotoxicity**, not optic neuritis. *Inhibition of mycolic acid synthesis* - This describes the mechanism of action of **isoniazid**, a cornerstone anti-TB drug. - Isoniazid's main side effects are **hepatotoxicity** and **peripheral neuropathy**, which is often prevented by **pyridoxine (vitamin B6) supplementation**. *Induction of free radical metabolites* - This is the mechanism by which **pyrazinamide** is thought to act, although its precise mechanism is not fully understood. - Pyrazinamide is primarily associated with **hepatotoxicity** and **hyperuricemia** leading to **gout**, not optic neuritis.

Question 106: A 32-year-old man is brought to the emergency department with fever, dyspnea, and impaired consciousness. His wife reports that he has also had an episode of dark urine today. Two weeks ago, he returned from a trip to the Republic of Congo. His temperature is 39.4°C (103°F), pulse is 114/min, and blood pressure is 82/51 mm Hg. Physical examination shows scleral icterus. Decreased breath sounds and expiratory crackles are heard on auscultation of the lungs bilaterally. His hemoglobin concentration is 6.3 g/dL. A blood smear shows red blood cells with normal morphology and ring-shaped inclusions. Further laboratory testing shows normal rates of NADPH production. Which of the following is the most appropriate pharmacotherapy for this patient?

A. Proguanil
B. Dapsone
C. Chloroquine
D. Artesunate (Correct Answer)
E. Atovaquone

Explanation: ***Artesunate*** - This patient presents with **severe malaria**, indicated by fever, impaired consciousness, hypotension, dyspnea, dark urine (hemoglobinuria), scleral icterus (hemolysis), and anemia, following travel to an endemic area (Republic of Congo). The blood smear finding of **ring-shaped inclusions** with normal red cell morphology is characteristic of **Plasmodium falciparum** infection. - **Artesunate** is the drug of choice for **severe malaria** due to its rapid parasitic clearance and superior efficacy compared to other antimalarials, especially in regions with high chloroquine resistance, as is typical in the Republic of Congo for *P. falciparum*. *Proguanil* - Proguanil is primarily used in **malaria prophylaxis** or in combination with other drugs (e.g., atovaquone-proguanil) for uncomplicated malaria. - It is not indicated as monotherapy for **severe *P. falciparum* malaria**, nor is it suitable for emergency treatment of life-threatening infections. *Dapsone* - Dapsone is an **antibiotic** primarily used in the treatment of **leprosy** and prevention of *Pneumocystis jirovecii* pneumonia or toxoplasmosis in immunocompromised patients. - It has **no significant role** in the treatment of malaria, especially severe *P. falciparum* infection. *Chloroquine* - Chloroquine was historically a first-line treatment for malaria but is largely ineffective against **chloroquine-resistant *P. falciparum***, which is widely prevalent in the Republic of Congo and contributes to severe disease. - Administering chloroquine in this context would likely lead to **treatment failure** and worsening of the patient's severe condition. *Atovaquone* - Atovaquone, usually combined with proguanil (Malarone), is effective for **uncomplicated malaria** and prophylaxis. - However, it is **not the preferred agent for severe malaria** due to slower action and lack of intravenous formulation for initial critical management.

Question 107: A 55-year-old male with a 60 pack-year smoking history presents to his oncologist for ongoing management of his recently diagnosed small cell lung cancer. His oncologist discusses several options and decides to start the chemotherapeutic medication, etoposide. The patient is warned that one side effect of this drug is myelosuppression so he should be vigilant for development of any infectious symptoms. The beneficial effect of this drug in treating cancer is most likely due to which of the following effects?

A. DNA intercalation
B. Crosslinking of DNA
C. Stabilization of microtubules
D. Alkylation of DNA
E. Inhibition of supercoil relaxation (Correct Answer)

Explanation: ***Inhibition of supercoil relaxation*** - **Etoposide** is a **topoisomerase II inhibitor**, preventing DNA uncoiling and replication, thus causing DNA strand breaks and **apoptosis** in rapidly dividing cancer cells. - This mechanism specifically targets the enzyme responsible for managing the topological state of DNA, a crucial process during cell division. *DNA intercalation* - **DNA intercalation** involves drugs inserting themselves between the base pairs of DNA, distorting its structure and inhibiting replication and transcription (e.g., **doxorubicin**). - This is not the primary mechanism of action for **etoposide**, which directly interferes with topoisomerase II enzymes. *Crosslinking of DNA* - **Crosslinking of DNA** involves forming covalent bonds within or between DNA strands, preventing DNA replication and transcription (e.g., **cisplatin**, **cyclophosphamide**). - While effective in chemotherapy, this mechanism is characteristic of **alkylating agents** and is distinct from how etoposide operates. *Stabilization of microtubules* - **Stabilization of microtubules** (e.g., **paclitaxel**, **docetaxel**) or destabilization (e.g., **vincristine**, **vinblastine**) are mechanisms of **microtubule-targeting agents** that disrupt cell division. - **Etoposide** does not primarily affect microtubules but rather targets **DNA topoisomerases**. *Alkylation of DNA* - **Alkylation of DNA** involves the addition of an alkyl group to DNA bases, leading to DNA damage, miscoding, and ultimately cell death. - This mechanism is typical of **alkylating agents** like **cyclophosphamide** and **busulfan**, but it is not the primary mode of action for **etoposide**.

Question 108: A 23-year-old woman is brought to the emergency department 30 minutes after stepping on a piece of broken glass. Physical examination shows a 3-cm, ragged laceration on the plantar aspect of the left foot. The physician uses hydrogen peroxide to clean the wound. Which of the following is the most likely mechanism of action of this disinfectant?

A. Formation of free radicals (Correct Answer)
B. Intercalation of DNA
C. Crosslinking of proteins
D. Halogenation of nucleic acids
E. Congealing of cytoplasm

Explanation: ***Formation of free radicals*** - **Hydrogen peroxide** acts as an **oxidizing agent**, generating highly reactive **oxygen-free radicals** (e.g., superoxide, hydroxyl radicals) that damage microbial cellular components. - This **oxidative damage** disrupts proteins, lipids, and nucleic acids, leading to bacterial and viral cell death. *Intercalation of DNA* - This mechanism is characteristic of certain **chemotherapeutic agents** (e.g., doxorubicin, ethidium bromide) and some **antimicrobials**, which insert themselves between DNA base pairs, disrupting replication and transcription. - Hydrogen peroxide does not typically target DNA in this manner for its disinfectant action. *Crosslinking of proteins* - This mechanism is characteristic of **aldehydes** like **formaldehyde** and **glutaraldehyde**, which form covalent bonds between amino groups of proteins, denaturing them and disrupting cellular function. - While hydrogen peroxide can modify proteins, its primary disinfectant action is not through widespread protein crosslinking. *Halogenation of nucleic acids* - This mechanism is primarily associated with **halogens** such as **chlorine** and **iodine**, which react with nucleic acids to form halogenated compounds, thereby inactivating them. - Hydrogen peroxide, while an oxidizer, does not lead to halogenation as its primary mode of action. *Congealing of cytoplasm* - This mechanism, which refers to the coagulation or solidification of cellular contents, is typical of **alcohols** (e.g., ethanol, isopropanol) and some **heavy metal salts** that denature proteins and lipids, leading to cell lysis. - Hydrogen peroxide's action is more specific to oxidative damage rather than general cytoplasmic congealing.

Question 109: A 19-year-old woman presents with abdominal pain and diarrhea for the last week. She has missed 3 days of school and is extremely stressed about the effect of this absence on her academic performance. She has had a couple of similar though less intense episodes in the past. She says that the diarrhea alternates with constipation and is associated with bloating and flatus. She describes the abdominal pain as spasmodic and episodic, sometimes radiating to the legs, with each episode lasting for 10–15 minutes and relieved by defecation. The patient denies any change in the color of her feces, increased frequency of urination or burning during micturition, loss of appetite or weight loss. No significant past medical history. No significant family history. Physical examination is unremarkable. Laboratory investigations are normal. Which of the following would the best choice to manage the diarrheal symptoms in this patient?

A. Dicyclomine
B. Sulfasalazine
C. Loperamide (Correct Answer)
D. Norfloxacin + metronidazole
E. Metronidazole

Explanation: ***Loperamide*** - This patient presents with symptoms consistent with **Irritable Bowel Syndrome (IBS)**, characterized by chronic abdominal pain, bloating, and altered bowel habits (diarrhea alternating with constipation), exacerbated by stress. - **Loperamide** is an **opioid receptor agonist** that decreases gut motility and fluid secretion, effectively treating the **diarrheal component** of IBS without causing central nervous system effects. *Dicyclomine* - **Dicyclomine** is an **anticholinergic/antispasmodic** agent used to reduce **abdominal pain and cramping** in IBS by relaxing smooth muscle in the gut. - While it can help with the spasmodic pain described, it is not the best choice for managing the *diarrheal symptoms* specifically, which is what the question asks for. *Sulfasalazine* - **Sulfasalazine** is an **anti-inflammatory drug** primarily used in the treatment of **inflammatory bowel disease (IBD)** like ulcerative colitis and Crohn's disease, as well as rheumatoid arthritis. - The patient's presentation with normal laboratory investigations and absence of red flag symptoms (e.g., weight loss, nocturnal symptoms, blood in stool) makes IBD unlikely. *Norfloxacin + metronidazole* - This combination is an antibiotic regimen typically used for treating **bacterial gastroenteritis** or specific parasitic infections. - The patient's symptoms are chronic and recurrent, not acute infectious, and laboratory investigations are normal, making bacterial infection an unlikely cause. *Metronidazole* - **Metronidazole** is an antibiotic effective against certain **anaerobic bacteria and parasites** (e.g., *Giardia*, *Clostridium difficile*). - Given the chronic nature of the symptoms, normal labs, and absence of specific infectious indicators, metronidazole is not indicated as a primary treatment.

Question 110: A 27-year-old male presents to urgent care complaining of pain with urination. He reports that the pain started 3 days ago. He has never experienced these symptoms before. He denies gross hematuria or pelvic pain. He is sexually active with his girlfriend, and they consistently use condoms. When asked about recent travel, he admits to recently returning from a “boys' trip" in Cancun where he had unprotected sex 1 night with a girl he met at a bar. The patient’s medical history includes type I diabetes that is controlled with an insulin pump. His mother has rheumatoid arthritis. The patient’s temperature is 99°F (37.2°C), blood pressure is 112/74 mmHg, and pulse is 81/min. On physical examination, there are no lesions of the penis or other body rashes. No costovertebral tenderness is appreciated. A urinalysis reveals no blood, glucose, ketones, or proteins but is positive for leukocyte esterase. A urine microscopic evaluation shows a moderate number of white blood cells but no casts or crystals. A urine culture is negative. Which of the following is the most likely cause for the patient’s symptoms?

A. Herpes simplex virus
B. Chlamydia trachomatis (Correct Answer)
C. Treponema pallidum
D. Neisseria gonorrhoeae
E. Mycobacterium tuberculosis

Explanation: ***Chlamydia trachomatis*** - The patient's symptoms of **dysuria** and **leukocyte esterase** on urinalysis, coupled with a **negative urine culture**, are highly suggestive of a sexually transmitted infection. - Given his recent unprotected sexual encounter, **Chlamydia trachomatis** is a common cause of **nongonococcal urethritis (NGU)** that fits this clinical picture. - Chlamydia is an **intracellular organism** that does not grow on routine bacterial culture media, explaining the negative urine culture despite pyuria. *Herpes simplex virus* - HSV typically causes **painful vesicular or ulcerative lesions** on the genitalia, which are not described in this patient. - While it can cause dysuria, it's usually secondary to these visible lesions, and the primary complaint here is isolated dysuria without external lesions. *Treponema pallidum* - This causes **syphilis**, which typically presents with a **painless chancre** in its primary stage or a rash in its secondary stage. - It does not commonly cause isolated dysuria or signs of urethritis like leukocyte esterase without other prominent features. *Neisseria gonorrhoeae* - While *N. gonorrhoeae* can also cause urethritis with a negative routine urine culture, it typically presents with **profuse purulent urethral discharge**, which is not described in this patient. - The absence of significant discharge and the clinical presentation are more consistent with **nongonococcal urethritis (NGU)**, of which Chlamydia is the most common cause. - Both organisms require nucleic acid amplification tests (NAATs) for definitive diagnosis, as they may not grow on routine bacterial culture. *Mycobacterium tuberculosis* - **Genitourinary tuberculosis** is a rare cause of dysuria and often presents with more chronic symptoms, sometimes with sterile pyuria, but would not be the initial suspicion for acute dysuria following a single unprotected sexual encounter. - It typically involves other systemic symptoms or evidence of TB elsewhere.

Question 111: A 23-year-old woman comes to the emergency department because of a diffuse, itchy rash and swollen face for 6 hours. That morning, she was diagnosed with an abscess of the lower leg. She underwent treatment with incision and drainage as well as oral antibiotics. She has no history of serious illness. She is not in acute distress. Her temperature is 37.2°C (99°F), pulse is 78/min, and blood pressure is 128/84 mm Hg. Physical examination shows mild swelling of the eyelids and lips. There are multiple erythematous patches and wheals over her upper extremities, back, and abdomen. The lungs are clear to auscultation. Cardiac examination shows no abnormalities. After discontinuing all recently administered drugs and beginning continuous vital sign monitoring, which of the following is the most appropriate next step in management?

A. Endotracheal intubation and mechanical ventilation
B. Intramuscular epinephrine and intravenous hydrocortisone administration
C. Oral diphenhydramine and close monitoring (Correct Answer)
D. Intravenous famotidine administration
E. Watchful waiting and regular reassessments

Explanation: ***Oral diphenhydramine and close monitoring*** - The patient presents with **urticaria** (itchy wheals) and **angioedema** (swelling of eyelids and lips) following antibiotic administration, consistent with a mild-to-moderate allergic reaction. - **Antihistamines** (H1 blockers like diphenhydramine) are **first-line treatment** for urticaria and angioedema, providing symptomatic relief by blocking histamine receptors. - With stable vital signs and no signs of anaphylaxis, oral antihistamine therapy combined with close monitoring for potential progression is the most appropriate management. - Monitoring is essential to detect any worsening symptoms that might require escalation of care. *Watchful waiting and regular reassessments* - While monitoring is important after discontinuing the offending agent, **watchful waiting alone is insufficient** when a patient has active allergic symptoms like urticaria and angioedema. - Active symptoms require symptomatic treatment with antihistamines, not just observation. - This approach would leave the patient symptomatic without addressing the ongoing histamine-mediated reaction. *Endotracheal intubation and mechanical ventilation* - This aggressive intervention is only indicated for **impending or actual airway compromise**, such as severe laryngeal edema causing stridor or respiratory failure. - The patient has clear lungs, stable vital signs, and only mild facial swelling without respiratory symptoms, indicating no immediate threat to airway patency. *Intramuscular epinephrine and intravenous hydrocortisone administration* - **Epinephrine** is the first-line treatment for **anaphylaxis**, characterized by respiratory compromise (bronchospasm, stridor) and/or cardiovascular instability (hypotension, tachycardia). - This patient has **stable vital signs** (normal BP, normal pulse), clear lungs, and no signs of systemic compromise, ruling out anaphylaxis. - **Hydrocortisone** may be used as adjunctive therapy in severe reactions but is not indicated for uncomplicated urticaria and angioedema. *Intravenous famotidine administration* - **Famotidine** (H2 blocker) can be used as **adjunctive therapy** with H1 blockers for allergic reactions but is not first-line treatment. - H1 antihistamines (like diphenhydramine) are more effective for urticaria and angioedema and should be administered first. - IV administration is unnecessary when oral route is available and the patient is not in distress.

Question 112: A 24-year-old woman comes to the emergency department because of a 4-hour history of headaches, nausea, and vomiting. During this time, she has also had recurrent dizziness and palpitations. The symptoms started while she was at a friend's birthday party, where she had one beer. One week ago, the patient was diagnosed with a genitourinary infection and started on antimicrobial therapy. She has no history of major medical illness. Her pulse is 106/min and blood pressure is 102/73 mm Hg. Physical examination shows facial flushing and profuse sweating. The patient is most likely experiencing adverse effects caused by treatment for an infection with which of the following pathogens?

A. Candida albicans
B. Chlamydia trachomatis
C. Neisseria gonorrhoeae
D. Herpes simplex virus
E. Trichomonas vaginalis (Correct Answer)

Explanation: ***Trichomonas vaginalis*** - The patient's symptoms (headache, nausea, vomiting, dizziness, palpitations, facial flushing, sweating) after consuming alcohol while on antimicrobial therapy for a genitourinary infection are characteristic of a **disulfiram-like reaction**. - **Metronidazole**, a common treatment for *Trichomonas vaginalis* infection, is known to cause a disulfiram-like reaction when combined with alcohol, due to inhibition of **acetaldehyde dehydrogenase**. *Candida albicans* - Genitourinary infections with *Candida albicans* (e.g., vulvovaginal candidiasis) are typically treated with **antifungal medications** like fluconazole, which do not cause disulfiram-like reactions with alcohol. - While symptoms like headache can occur with some antifungals, the constellation of flushing, palpitations, and nausea after a single beer strongly points away from this pathogen. *Chlamydia trachomatis* - *Chlamydia trachomatis* is commonly treated with **azithromycin** or **doxycycline**, neither of which are associated with disulfiram-like reactions to alcohol. - The patient's symptoms are specific to alcohol interaction with certain antimicrobials, not typical side effects of these antibiotics. *Neisseria gonorrhoeae* - Infections with *Neisseria gonorrhoeae* are usually treated with **ceftriaxone** (often with azithromycin), which also do not cause disulfiram-like reactions. - The clinical presentation after alcohol consumption is inconsistent with the typical adverse effects of these treatments. *Herpes simplex virus* - Genitourinary infections caused by herpes simplex virus are treated with **antiviral medications** such as acyclovir or valacyclovir. - These antiviral drugs do not cause disulfiram-like reactions when ingested with alcohol.

Question 113: A 56-year-old man with a history of HIV presents with diarrhea. The patient has had diarrhea for the past week and it has been gradually worsening. The patient describes it as profuse and watery. He has lost 15 pounds during this time frame and feels very weak. The patient is not currently taking his antiretroviral medications and historically has been non-compliant with his medications. His temperature is 98.5°F (36.9°C), blood pressure is 122/58 mmHg, pulse is 127/min, respirations are 14/min, and oxygen saturation is 99% on room air. Physical exam is notable for an emaciated man who is tachycardic. Stool exam with a modified acid-fast stain reveals organisms. The patient is started on IV fluids. Which of the following is the best treatment for this patient?

A. Nitazoxanide (Correct Answer)
B. Metronidazole
C. Supportive therapy only
D. Mesalamine enema
E. Ciprofloxacin

Explanation: ***Nitazoxanide*** - The patient's presentation with **profuse watery diarrhea**, **weight loss**, and **non-compliance with HIV medications** in an immunosuppressed state, coupled with **acid-fast organisms in stool**, is highly suggestive of **Cryptosporidiosis**. - While the **most important treatment** for Cryptosporidiosis in HIV patients is **resumption of antiretroviral therapy (ART)** to restore immune function, **Nitazoxanide** is the best **antimicrobial agent** among the options listed. - Note that Nitazoxanide has **limited efficacy in severely immunocompromised patients** (CD4 <50-100), but it is still recommended as adjunctive therapy along with immune reconstitution. *Metronidazole* - This antibiotic is primarily used for anaerobic bacterial infections and parasitic infections such as **Giardia lamblia** and **Entamoeba histolytica**. - It is **not effective** against Cryptosporidium, which is identified by acid-fast staining. *Supportive therapy only* - While **IV fluids** are crucial for rehydration in severe diarrhea and weight loss, supportive care alone is **insufficient** to treat active Cryptosporidium infection in an immunocompromised patient. - The patient requires both **antimicrobial therapy** and, most importantly, **resumption of ART** for immune reconstitution. *Mesalamine enema* - **Mesalamine enemas** are anti-inflammatory medications used to treat inflammatory bowel diseases like **ulcerative colitis**, particularly in the rectum and lower colon. - They are **not indicated** for infectious diarrhea caused by parasites like Cryptosporidium. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic used for bacterial infections, including some causes of bacterial gastroenteritis. - It is **ineffective** against parasitic infections such as Cryptosporidiosis.

Question 114: A 62-year-old woman presents to her oncologist to discuss the chemotherapy options for her newly diagnosed breast cancer. During the meeting, they discuss a drug that inhibits the breakdown of mitotic spindles in cells. Her oncologist explains that this will be more toxic to cancer cells because those cells are dividing more rapidly. Which of the following side effects is closely associated with the use of this chemotherapeutic agent?

A. Photosensitivity
B. Peripheral neuropathy (Correct Answer)
C. Paralytic ileus
D. Hemorrhagic cystitis
E. Pulmonary fibrosis

Explanation: ***Peripheral neuropathy*** - Drugs that inhibit the breakdown of **mitotic spindles** are **microtubule-targeting agents** (e.g., **taxanes** like paclitaxel/docetaxel, **vinca alkaloids** like vincristine/vinblastine). - These agents interfere with **microtubule function** in neurons, leading to **axonal damage** and **peripheral neuropathy**. - This is the **most characteristic and common dose-limiting toxicity** of microtubule inhibitors, affecting sensory and motor nerves (numbness, tingling, weakness in extremities). *Photosensitivity* - **Photosensitivity** is a common adverse effect associated with certain chemotherapeutic agents like **fluorouracil** (5-FU) or **methotrexate**, but is not linked to microtubule inhibitors. - It involves an increased sensitivity to UV light, often manifesting as a rash or exaggerated sunburn. *Paralytic ileus* - **Paralytic ileus** can occur with **vinca alkaloids** (especially vincristine) due to autonomic neuropathy affecting the **enteric nervous system**. - However, this is **less common** than peripheral neuropathy and occurs more specifically with vincristine rather than taxanes. - **Peripheral neuropathy** is the more pervasive, dose-limiting, and universally characteristic side effect across all microtubule inhibitors. *Hemorrhagic cystitis* - **Hemorrhagic cystitis** is a classic side effect of **alkylating agents** like **cyclophosphamide** and **ifosfamide**, which produce the toxic metabolite **acrolein**. - It is prevented/managed with **mesna**, which inactivates acrolein. - Not associated with microtubule inhibitors. *Pulmonary fibrosis* - **Pulmonary fibrosis** is a known side effect of certain chemotherapeutic drugs, most notably **bleomycin** and **busulfan**. - This adverse effect is not associated with agents that target **mitotic spindle breakdown**.

Question 115: A 32-year-old female presents to her gynecologist complaining of heavy and irregular vaginal bleeding. One month ago, she underwent a dilation and curettage procedure to remove a hydatidiform mole. On examination, her uterus appears enlarged. Serum ß-hCG is highly elevated. Biopsy of her uterus reveals avillous proliferation of cytotrophoblasts and syncytiotrophoblasts. She is eventually diagnosed with choriocarcinoma and initiates treatment with a medication known to affect folate metabolism. Which of the following complications should this patient most likely be monitored for following initiation of the medication?

A. Hemorrhagic cystitis
B. Pulmonary fibrosis
C. Peripheral neuropathy
D. Cardiotoxicity
E. Bone marrow suppression (Correct Answer)

Explanation: ***Bone marrow suppression*** - The medication affecting folate metabolism used for choriocarcinoma is **methotrexate**, a folate antagonist that inhibits dihydrofolate reductase. - **Myelosuppression (bone marrow suppression)** is the **most common and clinically significant dose-limiting toxicity** of methotrexate, manifesting as pancytopenia with decreased white blood cells, red blood cells, and platelets. - Patients on methotrexate require **routine complete blood count (CBC) monitoring** before and during treatment to detect myelosuppression early. - Other important methotrexate toxicities include hepatotoxicity, nephrotoxicity, and mucositis, but bone marrow suppression is the primary concern requiring close monitoring. *Pulmonary fibrosis* - While methotrexate can rarely cause pulmonary toxicity, it typically presents as **acute pneumonitis** (hypersensitivity reaction) rather than chronic fibrosis. - Pulmonary toxicity occurs in <10% of patients and is more commonly associated with chronic low-dose methotrexate use (e.g., for rheumatoid arthritis) than high-dose chemotherapy. - This is not the most likely complication requiring routine monitoring. *Hemorrhagic cystitis* - **Hemorrhagic cystitis** is a characteristic complication of **cyclophosphamide** and **ifosfamide**, not methotrexate. - It results from toxic metabolite (acrolein) accumulation in the bladder and can be prevented with hydration and mesna. *Peripheral neuropathy* - **Peripheral neuropathy** is typically associated with **vinca alkaloids** (vincristine, vinblastine) and **taxanes** (paclitaxel, docetaxel), which disrupt microtubule function. - Methotrexate does not cause peripheral neuropathy as a primary toxicity. *Cardiotoxicity* - **Cardiotoxicity**, including dilated cardiomyopathy, is a well-known dose-dependent complication of **anthracyclines** (doxorubicin, daunorubicin). - Methotrexate is not associated with direct cardiac toxicity.

Question 116: A 67-year-old woman who was diagnosed with cancer 2 months ago presents to her oncologist with a 6-day history of numbness and tingling in her hands and feet. She is concerned that these symptoms may be related to progression of her cancer even though she has been faithfully following her chemotherapy regimen. She is not currently taking any other medications and has never previously experienced these symptoms. On physical exam, she is found to have decreased sensation to pinprick and fine touch over hands, wrists, ankles, and feet. Furthermore, she is found to have decreased reflexes throughout. Her oncologist assures her that these symptoms are a side effect from her chemotherapy regimen rather than progression of the cancer. The drug most likely responsible for her symptoms has which of the following mechanisms?

A. Alkylation of DNA
B. Inhibit folate metabolism
C. DNA strand breaking
D. Inhibit microtubule formation (Correct Answer)
E. Prevention of nucleotide synthesis

Explanation: ***Inhibit microtubule formation*** - The patient's symptoms of **numbness**, **tingling**, **decreased sensation** to pinprick and fine touch in a **stocking-glove distribution**, and **decreased reflexes** are characteristic of **peripheral neuropathy**. - **Vinca alkaloids** (e.g., vincristine) and **taxanes** (e.g., paclitaxel, docetaxel) are chemotherapy agents that **inhibit microtubule formation**, and **peripheral neuropathy is their classic dose-limiting toxicity**. - These agents are the **most strongly associated** with this specific adverse effect pattern among chemotherapy drugs. *Alkylation of DNA* - **Alkylating agents** (e.g., cyclophosphamide) and **platinum-based agents** (e.g., cisplatin, oxaliplatin) exert their cytotoxic effects by **cross-linking DNA strands**, preventing DNA replication and transcription. - While **cisplatin and oxaliplatin can cause significant peripheral neuropathy**, the **microtubule inhibitors** (vinca alkaloids and taxanes) are **more classically associated** with this side effect and are the expected answer in this clinical context. *Inhibit folate metabolism* - This mechanism is characteristic of **antimetabolites** like **methotrexate**, which **inhibits dihydrofolate reductase**, thereby disrupting DNA synthesis. - While methotrexate can have neurological side effects (particularly intrathecal administration causing neurotoxicity), **typical peripheral neuropathy is not its most common or direct adverse effect** related to this mechanism. *DNA strand breaking* - This mechanism is associated with agents like **etoposide** (a topoisomerase inhibitor) or **bleomycin** (which generates free radicals causing DNA strand breaks). - While these drugs have various toxicities, they are **not typically associated with peripheral neuropathy** as their primary or most prominent side effect. *Prevention of nucleotide synthesis* - This is a broad mechanism shared by many **antimetabolites** (e.g., 5-fluorouracil, hydroxyurea, cytarabine) that interfere with the synthesis of purines or pyrimidines. - While these agents can cause various adverse effects, **peripheral neuropathy is not a hallmark toxicity** as it is with drugs that target microtubules.

Question 117: A 69-year-old male with past medical history of hypertension, hyperlipidemia, and diabetes mellitus complicated by end stage renal disease on dialysis presents to his nephrologist for a follow-up appointment. A few weeks ago, the patient saw his nephrologist because he had been feeling tired despite efforts to get enough sleep, eat a well-balanced diet, and exercise. At the time, laboratory studies revealed a hemoglobin of 9.7 g/dL, and the patient’s nephrologist suggested starting recombinant human erythropoietin (EPO). Since then, the patient has been receiving EPO intravenously three times per week. The patient reports today that he continues to feel tired despite the new treatment. His temperature is 98.0°F (36.7°C), blood pressure is 134/83 mmHg, pulse is 65/min, and respirations are 12/min. On physical exam, he has conjunctival pallor, and laboratory studies show a hemoglobin of 9.8 g/dL. Which of the following laboratory findings would currently be seen in this patient?

A. Normal MCV, increased RDW, increased ferritin, increased transferrin saturation
B. Low MCV, increased RDW, increased ferritin, decreased transferrin saturation
C. Low MCV, increased RDW, normal ferritin, normal transferrin saturation
D. Normal MCV, normal RDW, increased ferritin, increased transferrin saturation
E. Low MCV, increased RDW, decreased ferritin, decreased transferrin saturation (Correct Answer)

Explanation: ***Low MCV, increased RDW, decreased ferritin, decreased transferrin saturation*** - The patient's persistent anemia despite **erythropoietin (EPO)** treatment, along with conjunctival pallor and an unchanged hemoglobin level, points towards an underlying **iron deficiency**. - **Iron deficiency** is characterized by **microcytic (low MCV)**, **hypochromic** red blood cells, often with an **increased red cell distribution width (RDW)** due to varying cell sizes, and labs showing **decreased ferritin** (iron stores) and **decreased transferrin saturation** (iron transport). *Normal MCV, increased RDW, increased ferritin, increased transferrin saturation* - This profile (**increased ferritin** and **transferrin saturation**) is inconsistent with **iron deficiency**, which is the likely cause of the patient's persistent anemia despite EPO. - While an **increased RDW** can be seen in some anemias, the other markers do not fit the clinical picture of uncorrected anemia. *Low MCV, increased RDW, increased ferritin, decreased transferrin saturation* - The presence of **increased ferritin** suggests sufficient or even elevated iron stores, which contradicts the classic picture of **iron deficiency anemia**. - **Decreased transferrin saturation** with **increased ferritin** can occur in **anemia of chronic disease (ACD)**, but the primary issue here is likely iron deficiency given the patient's ESRD and lack of response to EPO. *Low MCV, increased RDW, normal ferritin, normal transferrin saturation* - **Normal ferritin** and **normal transferrin saturation** would typically rule out **iron deficiency anemia** as the cause of microcytic anemia. - In a patient with end-stage renal disease (ESRD) and uncorrected anemia, **iron deficiency** is a common and often co-existing issue, making normal iron studies unlikely if iron deficiency is the problem. *Normal MCV, normal RDW, increased ferritin, increased transferrin saturation* - This profile suggests **adequate iron stores** and typically indicates a **normocytic anemia** (normal MCV) without significant variation in red cell size (normal RDW). - Given the patient's uncorrected anemia and the need for EPO, this laboratory picture does not align with the most likely cause of continued fatigue, which is an **iron deficiency**.

Question 118: A 23-year-old man is admitted to the hospital for observation because of a headache, dizziness, and nausea that started earlier in the day while he was working. He moves supplies for a refrigeration company and was handling a barrel of carbon tetrachloride before the symptoms began. He was not wearing a mask. One day after admission, he develops a fever and is confused. His temperature is 38.4°C (101.1°F). Serum studies show a creatinine concentration of 2.0 mg/dL and alanine aminotransferase concentration of 96 U/L. This patient's laboratory abnormalities are most likely due to which of the following processes?

A. Metabolite haptenization
B. Lipid peroxidation (Correct Answer)
C. Microtubule stabilization
D. Protoporphyrin accumulation
E. Glutathione depletion

Explanation: ***Lipid peroxidation*** - **Carbon tetrachloride (CCl4)** poisoning primarily causes liver and kidney damage through the formation of **CCl3• radical**, which triggers **lipid peroxidation** of cellular membranes. - This process leads to irreversible cell damage, manifesting as elevated liver enzymes (ALT) and kidney dysfunction (creatinine). - Lipid peroxidation is the **direct mechanism of cellular injury**, causing membrane disruption, organelle dysfunction, and cell death. *Metabolite haptenization* - While some toxins form **haptens** that can lead to immune-mediated injury, the primary mechanism of CCl4 toxicity is direct cellular damage via free radicals, not haptenization. - Haptenization typically involves a delayed hypersensitivity reaction, which is not the immediate and severe organ damage seen with CCl4. *Microtubule stabilization* - **Microtubule stabilization** is a mechanism of action for certain drugs (e.g., taxanes in chemotherapy) that interfere with cell division, but it is not a direct mechanism of toxicity for CCl4. - CCl4 toxicity is characterized by membrane damage, not disruption of the cytoskeleton. *Protoporphyrin accumulation* - **Protoporphyrin accumulation** is characteristic of certain **porphyrias** or **lead poisoning**, where there are defects in heme synthesis. - This mechanism is unrelated to the direct oxidative damage caused by CCl4 and its free radical metabolites. *Glutathione depletion* - **Glutathione (GSH)** depletion occurs early in CCl4 toxicity, reducing the cell's antioxidant capacity and allowing free radical accumulation. - However, GSH depletion is an **upstream event** that facilitates damage, while **lipid peroxidation** is the **downstream direct mechanism** that actually destroys cellular membranes and causes organ injury. - The question asks for the process causing the laboratory abnormalities (liver and kidney damage), making lipid peroxidation the more direct and accurate answer.

Question 119: A 15-year-old boy presents to the emergency department after a rusty nail pierced through his right foot. He was able to pull out the nail, but is unable to walk on his foot. He believes he had all his shots as a child, but his mother is unsure and cannot recall the specific vaccination dates or details. His last documented tetanus vaccination was at age 12. The vital signs are within normal limits. Physical examination reveals a 0.5-inch puncture wound on the right heel. The site is tender, erythematous, with flecks of reddish-brown particles in the base. No blood or discharge is seen. Which of the following is the most appropriate next step in management?

A. Administer DT
B. Administer Td only
C. Clean and dress the wound only
D. Administer Td and TIG (Correct Answer)
E. Administer Tdap, Td, and TIG (tetanus immune globulin)

Explanation: ***Administer Td and TIG*** - This patient has a **dirty wound** (rusty nail, reddish-brown particles indicating contamination) with **uncertain immunization history** (mother cannot recall vaccination details or confirm completion of primary series). - Although the last documented tetanus vaccination was at age 12 (3 years ago), the **uncertainty about whether the primary vaccination series was completed** necessitates treating this as an incomplete immunization history. - For dirty wounds with uncertain/incomplete immunization history, both **Td (active immunity)** and **Tetanus Immune Globulin/TIG (immediate passive immunity)** are required per CDC guidelines. - TIG provides immediate protection against circulating tetanus toxin while Td stimulates the patient's own immune response. *Administer DT* - **DT** (diphtheria and tetanus toxoids) is formulated for children **younger than 7 years old**. - This patient is 15 years old, so **Td** (adult formulation with reduced diphtheria component) is the appropriate vaccine. *Administer Td only* - While a **Td booster** addresses active immunity, it takes **2-4 weeks** to produce protective antibody levels. - For a **high-risk dirty wound with uncertain immunization history**, this delayed protection is insufficient. - **TIG is essential** to provide immediate passive immunity and neutralize any tetanus toxin that may be produced before the Td vaccine becomes effective. *Clean and dress the wound only* - **Wound care** (cleaning, irrigation, debridement of devitalized tissue) is essential but **insufficient** as sole management. - Given the high-risk wound and uncertain immunization history, **tetanus prophylaxis is mandatory** to prevent potentially fatal tetanus infection. *Administer Tdap, Td, and TIG (tetanus immune globulin)* - Administering both **Tdap and Td simultaneously is redundant** and not recommended. - **Tdap** (which includes pertussis) can be used instead of Td for wound prophylaxis if the patient has never received Tdap, but giving both Tdap AND Td is unnecessary. - While TIG is appropriate for this scenario, the dual vaccine administration (Tdap + Td) is **not standard practice**.

Question 120: A 65-year-old man comes to the physician because of a 1-month history of progressive back pain. He has also had a 5-kg (11-lb) weight loss over the past 3 months. His only medications are a daily multivitamin and ibuprofen, which he takes daily for the back pain. Physical examination shows tenderness to palpation over the lower spine and the left iliac crest. His hemoglobin concentration is 9.3 g/dL, his serum calcium concentration is 12 mg/dL, and his serum creatinine concentration is 2.1 mg/dL. A bone marrow biopsy shows 21% plasma cells. A diagnosis of multiple myeloma is established. In preparation for an autologous hematopoietic stem cell transplantation, the patient receives a myeloablative treatment regimen that includes busulfan. Which of the following drugs acts via a similar mechanism of action to busulfan?

A. Etoposide
B. Vemurafenib
C. Vincristine
D. Cytarabine
E. Lomustine (Correct Answer)

Explanation: ***Lomustine*** - Both **busulfan** and **lomustine** are **alkylating agents**. They act by transferring **alkyl groups** to DNA, leading to cross-linking of DNA strands and inhibition of DNA synthesis and function. - This **DNA damage** results in cell cycle arrest and apoptosis, particularly in rapidly dividing cells like cancer cells. *Etoposide* - **Etoposide** is a **topoisomerase II inhibitor** that prevents DNA relegation after strand breaks, leading to DNA damage and cell death. - While it also targets DNA, its mechanism is distinct from the alkylation process of busulfan. *Vemurafenib* - **Vemurafenib** is a **BRAF kinase inhibitor** used in melanoma treatment. It specifically targets the **BRAF V600E mutation**. - Its mechanism involves blocking signal transduction pathways critical for cell proliferation, rather than directly damaging DNA. *Vincristine* - **Vincristine** is a **vinca alkaloid** that acts as a **microtubule inhibitor**, preventing the formation of the **mitotic spindle** during cell division. - This leads to metaphase arrest and apoptosis, a mechanism fundamentally different from DNA alkylation. *Cytarabine* - **Cytarabine** is an **antimetabolite**, specifically a **pyrimidine analog**, that inhibits **DNA polymerase**. - It gets incorporated into DNA, leading to chain termination and inhibition of DNA synthesis and repair, making its action different from direct DNA alkylation.

Question 121: A 40-year-old man with AIDS comes to the physician because of a 3-week history of intermittent fever, abdominal pain, and diarrhea. He has also had a nonproductive cough and a 3.6-kg (8-lb) weight loss in this period. He was treated for pneumocystis pneumonia 2 years ago. He has had skin lesions on his chest for 6 months. Five weeks ago, he went on a week-long hiking trip in Oregon. Current medications include efavirenz, tenofovir, and emtricitabine. He says he has had trouble adhering to his medication. His temperature is 38.3°C (100.9°F), pulse is 96/min, and blood pressure is 110/70 mm Hg. Examination shows oral thrush on his palate and a white, non-scrapable plaque on the left side of the tongue. There is axillary and inguinal lymphadenopathy. There are multiple violaceous plaques on the chest. Crackles are heard on auscultation of the chest. Abdominal examination shows mild, diffuse tenderness throughout the lower quadrants. The liver is palpated 2 to 3 cm below the right costal margin, and the spleen is palpated 1 to 2 cm below the left costal margin. Laboratory studies show: Hemoglobin 12.2 g/dL Leukocyte count 4,800/mm3 CD4+ T-lymphocytes 44/mm3 (Normal ≥ 500 mm3) Platelet count 258,000/mm3 Serum Na+ 137 mEq/L Cl- 102 mEq/L K+ 4.9 mEq/L Alkaline phosphatase 202 U/L One set of blood culture grows acid-fast organisms. A PPD skin test shows 4 mm of induration. Which of the following is the most appropriate pharmacotherapy for this patient's condition?

A. Rifampin and isoniazid
B. Voriconazole
C. Erythromycin
D. Amphotericin B and itraconazole
E. Azithromycin and ethambutol (Correct Answer)

Explanation: ***Azithromycin and ethambutol*** - This patient presents with disseminated **Mycobacterium avium complex (MAC)** infection, evidenced by systemic symptoms (fever, weight loss, abdominal pain, diarrhea), **hepatosplenomegaly**, elevated alkaline phosphatase, and the isolation of **acid-fast organisms** from blood cultures in an HIV-positive patient with a **CD4 count of 44 cells/mm³**. Azithromycin (or clarithromycin) in combination with ethambutol is the recommended treatment for disseminated MAC. - The diagnosis is further supported by the patient's history of non-adherence to ART, leading to a severely immunocompromised state, and the fact that MAC is a common opportunistic infection in patients with **AIDS and CD4 counts below 50 cells/mm³**. *Rifampin and isoniazid* - This combination is part of the standard regimen for **Mycobacterium tuberculosis** infection. While the patient has acid-fast organisms, his low **CD4 count** and disseminated symptoms are more characteristic of MAC than typical pulmonary tuberculosis, especially given the rapid dissemination. - The PPD induration of 4mm is not diagnostic of active tuberculosis in an immunocompromised patient; a PPD response can be blunted in severe immunodeficiency. *Voriconazole* - **Voriconazole** is an antifungal medication primarily used to treat serious fungal infections, such as invasive aspergillosis, candidiasis, and scedosporiosis. - The patient's presentation with acid-fast organisms from blood culture indicates a bacterial infection, not a fungal infection, making voriconazole inappropriate. *Erythromycin* - **Erythromycin** is a macrolide antibiotic, but it is not the preferred or effective treatment for disseminated MAC. While macrolides like azithromycin and clarithromycin are used, erythromycin has generally fallen out of favor for mycobacterial infections due to its inferior efficacy and higher gastrointestinal side effects compared to newer macrolides. - It is typically used for common bacterial respiratory tract infections, skin infections, and sexually transmitted infections, but not for opportunistic mycobacterial infections in immunocompromised patients. *Amphotericin B and itraconazole* - **Amphotericin B** and **itraconazole** are antifungals used for systemic fungal infections (e.g., blastomycosis, histoplasmosis, cryptococcosis, aspergillosis). - The isolation of **acid-fast organisms** from blood culture confirms a mycobacterial infection, not a fungal one, hence these antifungals would not be effective.

Question 122: For which patient would isoniazid monotherapy be most appropriate?

A. 50-year-old male with positive PPD, active tuberculosis and poor compliance to multidrug regimens
B. 25-year-old female with positive PPD and acid-fast bacilli on sputum stain
C. 41-year-old female with positive PPD and a Ghon complex on chest radiograph
D. 37-year-old male with positive PPD and no clinical signs or radiographic evidence of disease (Correct Answer)
E. 31-year-old male with negative PPD but recent exposure to someone with active tuberculosis

Explanation: ***37-year-old male with positive PPD and no clinical signs or radiographic evidence of disease*** - This patient has **latent tuberculosis infection (LTBI)**, characterized by a positive PPD (indicating immune response to TB exposure) with no symptoms or radiographic findings of active disease. - **Isoniazid monotherapy** (6-9 months) is the standard treatment for LTBI to prevent progression to active tuberculosis. - This is the classic indication for isoniazid monotherapy. *50-year-old male with positive PPD, active tuberculosis and poor compliance to multidrug regimens* - This patient has **active tuberculosis**, which absolutely requires **multidrug therapy** (minimum 4 drugs: isoniazid, rifampin, pyrazinamide, and ethambutol) regardless of compliance issues. - Isoniazid monotherapy in active TB would rapidly lead to **drug resistance** and treatment failure. - Poor compliance is managed with directly observed therapy (DOT), not by simplifying to monotherapy. *25-year-old female with positive PPD and acid-fast bacilli on sputum stain* - **Acid-fast bacilli on sputum stain** confirms **active pulmonary tuberculosis**, which requires multidrug therapy. - Isoniazid monotherapy would be inadequate and promote drug resistance. *41-year-old female with positive PPD and a Ghon complex on chest radiograph* - A **Ghon complex** (calcified granuloma with associated lymph node) represents a **healed primary TB infection**. - While this patient may have LTBI (positive PPD), the presence of radiographic findings requires further evaluation to rule out active or reactivation TB before considering monotherapy. - Standard practice would include additional workup (sputum cultures, clinical assessment) rather than proceeding directly to monotherapy. *31-year-old male with negative PPD but recent exposure to someone with active tuberculosis* - A **negative PPD** can occur during the **window period** (initial 8-10 weeks after exposure before the immune response develops). - While **post-exposure prophylaxis** may be considered in recent close contacts per CDC guidelines (with repeat testing in 8-10 weeks), the patient with documented LTBI (positive PPD without active disease) remains the most clear-cut indication for isoniazid monotherapy. - The correct answer represents the most straightforward and standard indication.

Question 123: A 32-year-old man is admitted to the hospital for evaluation of a 3-month history of insomnia, odynophagia, and irritability. He works in a metal refinery. He appears distracted and irritable. Oral examination shows inflammation of the gums and buccal mucosa with excessive salivation. Neurological examination shows a broad-based gait and an intention tremor in both hands. After treatment with dimercaprol is begun, his symptoms slowly improve. This patient was most likely exposed to which of the following?

A. Lead
B. Mercury (Correct Answer)
C. Arsenic
D. Copper
E. Iron

Explanation: **Mercury** - The constellation of **insomnia, odynophagia, irritability, gingivostomatitis, excessive salivation, broad-based gait, and intention tremor** is highly characteristic of **mercury poisoning** (also known as erethism or Mad Hatter's disease). - The patient's occupation in a **metal refinery** increases his risk of exposure to mercury vapor, and the improvement with **dimercaprol**, a chelating agent, supports this diagnosis. *Lead* - While lead poisoning can cause neurological symptoms like **neuropathy** and **encephalopathy** (especially in children), it typically presents with **abdominal pain**, **constipation**, **anemia**, and a **"lead line" on the gums**, which are not dominant features here. - Although **dimercaprol** can be used for severe lead poisoning, the specific combination of symptoms points away from lead. *Arsenic* - Arsenic poisoning often presents with **gastrointestinal symptoms** (vomiting, diarrhea), **garlic breath**, **neuropathy**, and **skin changes** such as hyperkeratosis and Mee's lines on the nails. - The described oral inflammation and specific neurological signs (intention tremor, broad-based gait) are less typical of arsenic. *Copper* - Copper toxicity (e.g., Wilson's disease) involves **liver disease**, **Kayser-Fleischer rings** in the cornea, and **basal ganglia dysfunction** causing tremor and dystonia. - The patient's symptoms, particularly the prominent gingivostomatitis and irritability, do not align well with copper toxicity. *Iron* - Acute iron poisoning typically occurs in young children and causes severe **gastrointestinal irritation**, **metabolic acidosis**, and **shock**. - Chronic iron overload (**hemochromatosis**) primarily affects the liver, pancreas, heart, and joints, and does not cause the neurological or oral symptoms seen in this patient.

Question 124: A 25-year-old man presents with jaw discomfort and the inability to open his mouth fully for about 3 days. About a week ago, he says he cut himself while preparing a chicken dinner but did not seek medical assistance. Five days after the original injury, he started noticing jaw discomfort and an inability to open his mouth completely. He has no history of a serious illness or allergies and takes no medications. The patient says he had received his primary tetanus series in childhood, and that his last booster was more than 10 years ago. His blood pressure is 125/70 mm Hg and temperature is 36.9℃ (98.5°F). On physical examination, the patient is unable to open his jaw wider than 2.5 cm. Head and neck examinations are otherwise unremarkable. There is a 5 cm linear shallow laceration with some granulation tissue on the right index finger without necrosis, erythema, or pus. After wound care and initiation of metronidazole, which of the following is the next best step in the management of this patient?

A. DTaP
B. Td
C. Tetanus immunoglobulin (TIG) (Correct Answer)
D. No further treatment is required
E. Tdap

Explanation: ***Tetanus immunoglobulin (TIG)*** - This patient presents with symptoms highly suggestive of **tetanus**, including **trismus** (lockjaw) and a recent puncture wound. TIG provides **passive immunity** with pre-formed antibodies that can neutralize circulating tetanus toxin, which is crucial for immediate treatment. - Given that his last tetanus booster was more than 10 years ago and he is symptomatic, immediate TIG is necessary to combat the toxin already produced by *Clostridium tetani*. - **Note**: A tetanus toxoid vaccine (Td or Tdap) should also be administered at a different site to provide active immunity, but TIG is the **priority** intervention for neutralizing existing toxin in a symptomatic patient. *DTaP* - **DTaP (diphtheria, tetanus, acellular pertussis)** is administered to **children younger than 7 years old**. This patient is 25 years old. - While it provides **active immunity**, its effect is not immediate and would not address the acute, life-threatening toxin effects already present in a symptomatic patient. *Td* - **Td (tetanus and diphtheria)** is a booster vaccine providing **active immunity** suitable for adults. - Like DTaP, it confers active immunity, which takes time to develop and would not provide immediate protection against the existing tetanus toxin in a symptomatic patient. However, Td should be administered alongside TIG at a different site as part of complete management. *No further treatment is required* - This patient is clearly symptomatic with **trismus** after a puncture wound and an outdated tetanus vaccination, indicating an active **tetanus infection**. - Without immediate intervention, tetanus can lead to severe muscle spasms, respiratory failure, and death, so further treatment is urgently required. *Tdap* - **Tdap (tetanus, diphtheria, acellular pertussis)** is an adult-formulation booster vaccine, primarily given to adolescents and adults, especially during pregnancy or when in contact with infants. - It provides **active immunity**, which is not effective in neutralizing the immediate effects of existing tetanus toxin in a symptomatic patient. However, Tdap should be administered alongside TIG at a different site as part of complete management.

Question 125: A 46-year-old woman presents to her family physician for a general wellness checkup with a chief complaint of high levels of anxiety over the past year. Her anxiety has started to affect her performance at work, making her even more anxious and concerned that she will lose her job. She started psychotherapy several months ago and has experienced minimal improvement in her symptoms from this treatment. The patient is vehemently opposed to beginning any pharmacologic treatment for anxiety; however, she is interested in potential herbal remedies and has started taking kava. She also takes vitamin D, a multivitamin, fish oil, protein powder, and drinks goat milk regularly. The patient works as a commercial sex worker and has a history of IV drug abuse and alcohol abuse which she states she has not used in over a year. She has chronic tension headaches for which she self-administers acetaminophen usually multiple times per day. Her last wellness appointment was unremarkable and these problems are new. Laboratory values are ordered as seen below. Hemoglobin: 13 g/dL Hematocrit: 38% Leukocyte count: 6,870/mm^3 with normal differential Platelet count: 227,000/mm^3 Serum: Na+: 138 mEq/L Cl-: 102 mEq/L K+: 4.1 mEq/L HCO3-: 25 mEq/L BUN: 20 mg/dL Glucose: 111 mg/dL Creatinine: 1.0 mg/dL Ca2+: 10.2 mg/dL AST: 82 U/L ALT: 90 U/L Which of the following is the most likely cause of this patient's lab derangements?

A. Acetaminophen
B. Chronic hepatitis C infection
C. Alcoholic hepatitis
D. Acute hepatitis B infection
E. Dietary supplement (Correct Answer)

Explanation: **Dietary supplement** - The elevated **AST** and **ALT** levels, while non-specific, combined with the patient's anxiety and use of **kava**, strongly suggest kava-induced liver injury. **Kava** is well-known for its potential hepatotoxicity. - Other supplements like **fish oil** and **multivitamins** are generally safe for the liver, and goat milk or protein powder are unlikely to cause significant transaminitis. *Acetaminophen* - While **acetaminophen** overdose can cause severe liver damage, the patient describes chronic use for headaches, not an acute overdose. Chronic therapeutic use of acetaminophen is less likely to cause such significant transaminase elevations without other signs of toxicity. - The presented lab values show isolated elevation of AST and ALT without other signs of acute liver failure (e.g., coagulopathy, jaundice) that would be expected with severe acetaminophen toxicity. *Chronic hepatitis C infection* - **Chronic hepatitis C** can cause elevated **AST** and **ALT**, especially in patients with a history of **IV drug abuse**. However, the transaminase levels are typically more fluctuating and often show a disproportionate AST/ALT ratio or higher elevations. - Given the recent onset of symptoms and new lab derangements, and the patient's recent change in supplement use, **kava-induced liver injury** is a more acute and plausible explanation for initial workup. *Alcoholic hepatitis* - **Alcoholic hepatitis** often presents with an **AST:ALT ratio of 2:1 or greater**, and the AST and ALT levels are usually not as high as seen here (often <500IU/L). The patient also claims to have stopped alcohol consumption over a year ago. - While the patient has a history of alcohol abuse, the timing and the specific enzyme pattern make it less likely than kava-induced injury, especially with reported abstinence. *Acute hepatitis B infection* - **Acute hepatitis B infection** can cause significant hepatocellular injury with elevated **AST** and **ALT**, which can be very high (>1000 U/L). However, the patient's history doesn't immediately suggest an acute exposure event. - Without further serological markers, differentiating it from other causes of acute liver injury is difficult, but the prompt onset and symptomology point away from a new acute hepatitis B infection without supportive history details.

Question 126: A 29-year-old woman presents to the physician with a blurred vision of her right eye over the past day. She has pain around her right eye during eye movement. She has a history of tingling in her left leg 5 months ago, which spontaneously resolved after 2 weeks. She takes no medications. Her blood pressure is 110/70 mm Hg, the pulse is 72/min, the respirations are 15/min, and the temperature is 36.5℃ (97.7℉). On physical examination, after illumination of the left eye and bilateral pupillary constriction, illumination of the right eye shows pupillary dilation. Fundoscopic examination shows optic disk swelling in the right eye. A color vision test shows decreased perception in the right eye. The remainder of the physical examination shows no abnormalities. A brain MRI shows several foci of hyperintensity in the periventricular and juxtacortical regions. Which of the following is the most appropriate next step in management?

A. Methylprednisolone (Correct Answer)
B. Carbamazepine
C. Plasma exchange
D. Intravenous immunoglobulin (IVIG)
E. Acyclovir

Explanation: ***Methylprednisolone*** - This patient presents with **optic neuritis** (blurred vision, pain with eye movement, afferent pupillary defect, optic disc swelling, decreased color perception) and a history of a prior neurological episode (tingling in the left leg), suggestive of **multiple sclerosis exacerbation**. **High-dose intravenous corticosteroids** like methylprednisolone are the cornerstone of acute MS relapse treatment to shorten the duration and severity of attacks. - While corticosteroids do not alter the long-term prognosis of MS, they are effective in speeding recovery from acute neurological deficits and are the **most appropriate initial management** for an acute flare. *Carbamazepine* - **Carbamazepine** is an anticonvulsant primarily used for **trigeminal neuralgia** and certain seizure disorders. It is not indicated for the acute treatment of optic neuritis or multiple sclerosis exacerbations. - It works by stabilizing inactivated sodium channels and is not effective in reducing inflammation or demyelination in MS flares. *Plasma exchange* - **Plasma exchange**, or plasmapheresis, is considered for **severe acute MS relapses** when there is a suboptimal response to high-dose corticosteroids. It is a second-line therapy, not the initial treatment. - While it can be effective in refractory cases, the first step is always corticosteroid therapy, as it is less invasive and generally well-tolerated. *Intravenous immunoglobulin (IVIG)* - **IVIG** is another treatment option for severe MS relapses, particularly when there are contraindications to corticosteroids or an inadequate response to steroids and plasma exchange. - Similar to plasma exchange, it is generally considered a **second-line or third-line treatment** and not the initial management for an acute MS exacerbation. *Acyclovir* - **Acyclovir** is an antiviral medication used to treat infections caused by herpes viruses, such as **herpes simplex virus (HSV)** and **varicella-zoster virus (VZV)**. - There is no indication of a viral infection causing the optic neuritis or neurological symptoms in this patient; therefore, acyclovir would not be an appropriate treatment.

Question 127: A 25-year-old medical student returns from a volunteer mission trip in Nicaragua with persistent cough and occasional hemoptysis for 3 weeks. A purified protein derivative test revealing a 20 mm wheal and a chest radiograph with hilar lymphadenopathy support a diagnosis of active tuberculosis. The patient is started on appropriate therapy. Among the prescribed medications, one drug inhibits carbohydrate polymerization of the pathogen's cell wall. What is the most likely complaint that the patient may present with because of this drug?

A. Leg numbness
B. Nausea and vomiting
C. Vision changes (Correct Answer)
D. Orange colored urine
E. Joint pain

Explanation: ***Vision changes*** - The drug that inhibits **carbohydrate polymerization** of the pathogen's cell wall is **ethambutol**. - Ethambutol's most significant side effect is **optic neuritis**, which can lead to **red-green color blindness** and **decreased visual acuity**. *Leg numbness* - **Leg numbness** or **peripheral neuropathy** is a common side effect of **isoniazid (INH)**, not ethambutol. - INH inhibits **mycolic acid synthesis** and its neurotoxic effects are due to vitamin B6 (pyridoxine) depletion. *Nausea and vomiting* - **Nausea and vomiting** are general gastrointestinal side effects that can occur with several anti-tuberculosis drugs, but are not specifically characteristic of the drug described. - **Pyrazinamide** is particularly known for causing gastrointestinal upset. *Orange colored urine* - **Orange-colored urine**, tears, and sweat are a classic side effect of **rifampin**, which inhibits **DNA-dependent RNA polymerase**. - This discoloration is harmless but important for patients to be aware of. *Joint pain* - **Joint pain** or **arthralgia** is a common side effect of **pyrazinamide**, often due to **hyperuricemia** caused by the drug. - It is not a characteristic side effect of ethambutol.

Question 128: A 67-year-old man is seen on the surgical floor after a transplant procedure. The previous day, the patient had a renal transplant from a matched donor. He is currently recovering and doing well. The patient has a past medical history of IV drug use, diabetes mellitus, oral cold sores, hypertension, renal failure, and dyslipidemia. The patient's current medications include lisinopril, atorvastatin, insulin, and aspirin. Prior to the procedure, he was also on dialysis. The patient is started on cyclosporine. The patient successfully recovers over the next few days. Which of the following medications should be started in this patient?

A. Azithromycin
B. TMP-SMX (Correct Answer)
C. Acyclovir
D. Low dose acyclovir
E. Penicillin

Explanation: ***TMP-SMX*** - **TMP-SMX (trimethoprim-sulfamethoxazole)** is the **most critical** prophylactic medication for all solid organ transplant recipients on immunosuppression. - It provides essential prophylaxis against **Pneumocystis jirovecii pneumonia (PJP)**, a life-threatening opportunistic infection with high mortality if not prevented. - PJP prophylaxis is a **universal recommendation** for all transplant patients and is typically continued for 6-12 months post-transplant. - Additionally offers protection against **Toxoplasma gondii**, **Nocardia**, and common urinary tract infections, making it particularly valuable in renal transplant recipients. *Azithromycin* - Azithromycin is a macrolide antibiotic used for specific bacterial infections and sometimes for **Mycobacterium avium complex (MAC)** prophylaxis in severely immunocompromised patients. - It is not standard prophylaxis in routine post-transplant care and does not protect against PJP, the most critical opportunistic infection in this setting. *Acyclovir* - High-dose acyclovir is used to **treat active HSV or VZV infections**, not for routine prophylaxis. - This patient has no active viral infection requiring treatment doses at this time. *Low dose acyclovir* - Low-dose acyclovir (or valacyclovir) is indeed used for **HSV/VZV prophylaxis** in transplant patients, especially those with a history of cold sores. - Many transplant centers do initiate this medication alongside TMP-SMX in the post-transplant period. - However, in a **single-best-answer** context, **TMP-SMX takes priority** as it prevents PJP, which is universally life-threatening and has higher incidence without prophylaxis compared to severe HSV reactivation. - TMP-SMX is considered the **essential first-line** prophylaxis that all transplant patients must receive. *Penicillin* - Penicillin is a narrow-spectrum antibiotic effective against certain gram-positive bacteria. - It has no role in post-transplant opportunistic infection prophylaxis and does not protect against PJP, HSV, or other transplant-related infections.

Question 129: A 49-year-old African American female with a history of chronic myeloid leukemia for which she is receiving chemotherapy presents to the emergency room with oliguria and colicky left flank pain. Her serum creatinine is 3.3 mg/dL. What is the preferred preventative therapy that could have been administered to this patient to prevent her complication of chemotherapy?

A. Diuresis
B. Acidification of the urine
C. Dialysis
D. Steroids
E. Allopurinol (Correct Answer)

Explanation: ***Allopurinol*** - The patient's presentation (oliguria, flank pain, elevated creatinine) indicates **acute kidney injury** from **tumor lysis syndrome (TLS)**, a common complication of chemotherapy for high-burden malignancies like chronic myeloid leukemia. - **Allopurinol**, a xanthine oxidase inhibitor, is the **standard preventative pharmacologic therapy** for TLS in patients at risk before starting chemotherapy. - It works by **blocking uric acid production**, preventing the hyperuricemia that leads to uric acid crystal deposition in renal tubules and subsequent acute kidney injury. - **Prophylactic allopurinol** (typically 300-600 mg/day) should be started **24-48 hours before chemotherapy** in high-risk patients and is the most commonly tested preventative agent for TLS on board examinations. *Diuresis* - **Aggressive IV hydration** (promoting diuresis) is indeed a critical component of TLS prevention, but it is **supportive care rather than specific pharmacologic therapy**. - While essential for maintaining renal perfusion and flushing metabolic byproducts, when the question asks for "preventative therapy," it typically refers to a **specific drug intervention** like allopurinol. - Hydration and allopurinol are used **together** in TLS prevention protocols. *Acidification of the urine* - This is **contraindicated** in TLS as **uric acid precipitates more readily in acidic urine**, worsening renal injury. - **Urine alkalinization** (with sodium bicarbonate) was historically used but is now controversial and less commonly recommended in modern protocols. *Dialysis* - Dialysis is a **treatment for established, severe TLS**, not a preventative measure. - It is reserved for life-threatening complications (severe hyperkalemia, refractory fluid overload, uremia) when medical management fails. *Steroids* - **Corticosteroids** have roles in certain malignancies but do not directly prevent the metabolic complications of tumor lysis syndrome. - They are not standard preventative therapy for TLS-induced kidney injury.

Question 130: A 71-year-old man with colorectal cancer comes to the physician for follow-up examination after undergoing a sigmoid colectomy. The physician recommends adjuvant chemotherapy with an agent that results in single-stranded DNA breaks. This chemotherapeutic agent most likely has an effect on which of the following enzymes?

A. DNA polymerase III
B. Topoisomerase I (Correct Answer)
C. Helicase
D. Telomerase
E. Topoisomerase II

Explanation: ***Topoisomerase I*** - **Topoisomerase I** creates **single-stranded DNA (ssDNA) breaks** to relieve torsional stress during DNA replication and transcription. - Many chemotherapeutic agents, such as camptothecin and its derivatives (e.g., irinotecan, topotecan), target topoisomerase I, leading to DNA damage and apoptosis in cancer cells. *DNA polymerase III* - **DNA polymerase III** is primarily involved in bacterial DNA replication, synthesizing new DNA strands in a 5' to 3' direction. - While essential for bacterial survival, it is not the target of chemotherapeutic agents that induce single-stranded DNA breaks in human cells. *Helicase* - **Helicase** is responsible for unwinding the DNA double helix during replication and transcription, separating the two strands. - While its function is critical for DNA processes, it does not directly create DNA breaks as its primary mechanism of action. *Telomerase* - **Telomerase** is an enzyme that maintains telomere length at the ends of chromosomes, particularly active in cancer cells. - Inhibitors of telomerase aim to shorten telomeres, leading to cellular senescence or apoptosis, but they do not primarily cause single-stranded DNA breaks. *Topoisomerase II* - **Topoisomerase II** creates **double-stranded DNA (dsDNA) breaks** to untangle and decatenate DNA. - Though also a target for chemotherapy (e.g., etoposide, doxorubicin), its mechanism involves double-stranded breaks, not single-stranded breaks as specified in the question.

Question 131: A 31-year-old woman presents to your office with one week of recurrent fevers. The highest temperature she recorded was 101°F (38.3°C). She recently returned from a trip to Nigeria to visit family and recalls a painful bite on her right forearm at that time. Her medical history is significant for two malarial infections as a child. She is not taking any medications. On physical examination, her temperature is 102.2°F (39°C), blood pressure is 122/80 mmHg, pulse is 80/min, respirations are 18/min, and pulse oximetry is 99% on room air. She has bilateral cervical lymphadenopathy and a visible, enlarged, mobile posterior cervical node. Cardiopulmonary and abdominal examinations are unremarkable. She has an erythematous induration on her right forearm. The most likely cause of this patient's symptoms can be treated with which of the following medications?

A. Sulfadiazine and pyrimethamine
B. Atovaquone and azithromycin
C. Primaquine
D. Chloroquine
E. Fexinidazole (Correct Answer)

Explanation: ***Fexinidazole*** - This patient's symptoms (recurrent fevers, cervical lymphadenopathy, erythematous induration after a trip to Nigeria with a painful bite) are highly suggestive of **African trypanosomiasis (sleeping sickness)**. - **Fexinidazole** is an oral nitroimidazole derivative approved for treating both first and second-stage human African trypanosomiasis (HAT) caused by *Trypanosoma brucei gambiense*. *Sulfadiazine and pyrimethamine* - This combination is primarily used to treat **toxoplasmosis**, an infection caused by the parasite *Toxoplasma gondii*. - While it can cause fever and lymphadenopathy, the travel history to Nigeria and a "painful bite" are not typical for toxoplasmosis transmission. *Atovaquone and azithromycin* - This combination is utilized for treating **Babesiosis**, a tick-borne parasitic infection. - While Babesiosis can cause fever and fatigue, the characteristic erythematous induration and prominent lymphadenopathy point away from this diagnosis. *Primaquine* - **Primaquine** is an antimalarial drug specifically used for the **radical cure of *Plasmodium vivax*** and ***Plasmodium ovale*** malaria, targeting the hypnozoite liver stages. - Although the patient has a history of malaria and a travel history to an endemic area, the current presentation with distinct lymphadenopathy and skin lesion points away from a straightforward malarial relapse or new infection primarily requiring primaquine as the sole treatment. *Chloroquine* - **Chloroquine** is an antimalarial drug, but its use is limited primarily to areas where **chloroquine-sensitive *Plasmodium falciparum*** strains are prevalent. - While the patient traveled to Nigeria, a region where malaria is endemic, the specific constellation of symptoms, including the bite and lymphadenopathy, is less characteristic of typical malaria than of trypanosomiasis.

Question 132: A drug that inhibits mRNA synthesis has the well-documented side effect of red-orange body fluids. For which of the following is this drug used as monotherapy?

A. Brucellosis
B. Tuberculosis
C. Methicillin-resistant staphylococcus aureus infection
D. Mycobacterium avium intracellulare infection
E. Neisseria meningitidis prophylaxis (Correct Answer)

Explanation: ***Neisseria meningitidis prophylaxis*** - The drug described is **rifampin**, which inhibits bacterial **DNA-dependent RNA polymerase**, thereby blocking **mRNA synthesis** and causes characteristic **red-orange discoloration of body fluids** (tears, urine, sweat). - Rifampin is used as **monotherapy** for **prophylaxis** against **Neisseria meningitidis** infection in close contacts of infected patients. - This is the **only indication** where rifampin monotherapy is appropriate, as prophylaxis requires short-term use where resistance development is not a concern. *Tuberculosis* - Rifampin is a **first-line agent** for tuberculosis treatment and a cornerstone of all TB regimens. - However, it is **never used as monotherapy** for TB due to rapid development of resistance. - Standard TB treatment requires **multidrug therapy** with rifampin, isoniazid, pyrazinamide, and ethambutol (RIPE) for initial phase. *Methicillin-resistant Staphylococcus aureus infection* - Rifampin is sometimes used in **combination** with other antibiotics (e.g., vancomycin, daptomycin) to treat **MRSA infections**, especially those involving **prosthetic devices** or **biofilms**. - It is **not used as monotherapy** for active MRSA infections due to extremely high rates of spontaneous resistance. *Mycobacterium avium intracellulare infection* - **Mycobacterium avium complex (MAC)** infections require a multidrug regimen, typically including **macrolides (azithromycin or clarithromycin)**, **ethambutol**, and sometimes **rifabutin** (a rifamycin derivative preferred over rifampin). - **Monotherapy is never appropriate** for MAC infections due to resistance concerns and treatment failure. *Brucellosis* - **Brucellosis** treatment requires **combination therapy**, typically **doxycycline plus rifampin** for 6 weeks or longer. - **Rifampin monotherapy** is inadequate for eradicating Brucella infection and leads to treatment failure and resistance development.

Question 133: A 52-year-old man presents to his physician with a chief concern of not feeling well. The patient states that since yesterday he has experienced nausea, vomiting, diarrhea, general muscle cramps, a runny nose, and aches and pains in his muscles and joints. The patient has a past medical history of obesity, chronic pulmonary disease, lower back pain, and fibromyalgia. His current medications include varenicline, oxycodone, and an albuterol inhaler. The patient is requesting antibiotics and a refill on his current medications at this visit. He works at a local public school and presented with a similar chief complaint a week ago, at which time he had his prescriptions refilled. You have also seen several of his coworkers this past week and sent them home with conservative measures. Which of the following is the best next step in management?

A. Oseltamivir
B. Azithromycin
C. Metronidazole
D. Methadone
E. Supportive therapy (Correct Answer)

Explanation: ***Supportive therapy*** - The patient's symptoms (nausea, vomiting, diarrhea, myalgias, flu-like symptoms) are highly suggestive of a **viral illness**, given the recent similar presentations in his coworkers where conservative measures were sufficient. - Antibiotics are ineffective against viral infections, and the patient has no signs or symptoms indicating a bacterial infection, making **supportive care** (hydration, rest, symptomatic relief) the most appropriate management. *Oseltamivir* - This antiviral medication is primarily used for the treatment of **influenza**, typically within 48 hours of symptom onset. - While the patient's symptoms are flu-like, the timing (symptoms began yesterday, and he presented a week ago with similar complaints) and the general viral presentation among coworkers make targeted antiviral therapy less indicated without a confirmed influenza diagnosis. *Azithromycin* - **Azithromycin is an antibiotic** used to treat bacterial infections, particularly respiratory tract infections, skin infections, and some sexually transmitted infections. - There is no indication of a bacterial infection in this patient; therefore, administering an antibiotic would be inappropriate and contribute to **antibiotic resistance**. *Metronidazole* - **Metronidazole is an antibiotic** primarily used for anaerobic bacterial infections and parasitic infections (e.g., *Clostridium difficile*, *Giardia*). - The patient's symptoms do not suggest these specific types of infections, making its use unwarranted. *Methadone* - **Methadone is an opioid analgesic** and is also used in medication-assisted treatment for opioid use disorder. - Prescribing methadone for the patient's current symptoms or for **opioid pain management** without further assessment, considering his current oxycodone prescription and potential for drug-seeking behavior given his request for refills, is inappropriate and potentially harmful.

Question 134: A 21-year-old girl with a history of bipolar disorder, now in a depressive episode, presents to the emergency in distress. She reports that she wanted to "end it all" and swallowed a full bottle of acetaminophen. However, regretting what it would do to her parents, and she decided that she wants to live. She appears in no acute distress and clearly states she swallowed the pills one hour ago. What is the most appropriate next step in management?

A. Give activated charcoal and test the urine for an acetaminophen level
B. Draw a serum acetaminophen level now
C. Give activated charcoal and draw a serum acetaminophen level now
D. Give activated charcoal and draw a serum acetaminophen in two hours
E. Give activated charcoal and draw a serum acetaminophen level in three hours (Correct Answer)

Explanation: ***Give activated charcoal and draw a serum acetaminophen level in three hours*** - **Activated charcoal** is crucial within 1-2 hours of ingestion to prevent absorption of the drug from the gastrointestinal tract. Since the patient presented 1 hour post-ingestion, this is still within the therapeutic window. - Drawing the serum acetaminophen level **in three hours from presentation** (i.e., 4 hours post-ingestion) allows for accurate plotting against the **Rumack-Matthew nomogram**, which requires levels drawn at least 4 hours after ingestion to reflect peak concentrations and guide antidote (N-acetylcysteine) administration. *Give activated charcoal and test the urine for an acetaminophen level* - While activated charcoal is indicated, a **urine test for acetaminophen level is not standard practice** for overdose management. - Acetaminophen levels are measured in **serum**, not urine, to determine toxicity and guide treatment. *Draw a serum acetaminophen level now* - Drawing a serum acetaminophen level *now* (one hour post-ingestion) is **too early** as the drug has not reached peak concentration. - An early level will be misleadingly low and cannot be reliably interpreted using the Rumack-Matthew nomogram, potentially leading to undertreatment of a serious overdose. *Give activated charcoal and draw a serum acetaminophen level now* - Giving activated charcoal is appropriate, but drawing a **serum level now (one hour post-ingestion) is too early** for accurate assessment of toxicity. - The level would not reflect the true peak concentration and could lead to inappropriate management decisions. *Give activated charcoal and draw a serum acetaminophen in two hours* - Giving activated charcoal is appropriate, but drawing the serum level **in two hours (3 hours post-ingestion) is still too early** for reliable interpretation using the Rumack-Matthew nomogram. - The standard is to draw levels **at or after 4 hours post-ingestion** to ensure adequate absorption and distribution.

Question 135: A 25-year-old woman with a psychiatric history of bipolar disorder is brought into the emergency department by emergency medical services. The patient is unconscious, but the mother states that she walked into the patient's room with the patient lying on the floor and an empty bottle of unknown pills next to her. The patient has previously tried to commit suicide 2 years ago. Upon presentation, the patient's vitals are HR 110, BP 105/60, T 99.5, RR 22. The patient soon has 5 episodes non-bilious non-bloody vomiting. Upon physical exam, she has pain in the right upper quadrant and her liver function tests are AST 1050 U/L, ALT 2050 U/L, ALP 55 U/L, Total Bilirubin 0.8 mg/dL, Direct Bilirubin 0.2 mg/dL. You are awaiting her toxicology screen. What is the most likely diagnosis?

A. Beta-blocker ingestion
B. Tricyclic antidepressant ingestion
C. Opiate ingestion
D. Acetaminophen ingestion (Correct Answer)
E. Salicylate ingestion

Explanation: ***Acetaminophen ingestion*** - The combination of a history of a **suicide attempt**, an **unknown pill overdose**, and profoundly elevated **AST and ALT** levels (in the thousands) points strongly to **acetaminophen toxicity**, which causes severe hepatotoxicity. - Initial symptoms like **nausea and vomiting** followed by signs of **liver damage** (RUQ pain, high liver enzymes) are classic for acetaminophen overdose. *Beta-blocker ingestion* - Manifests primarily with **cardiovascular effects** such as **bradycardia, hypotension, and AV block**, which are not consistently seen here (HR 110). - While it can cause some gastrointestinal upset, it does **not typically lead to such severe transaminitis**. *Tricyclic antidepressant ingestion* - Characterized by **anticholinergic effects** (e.g., dry mouth, blurred vision, urinary retention), **cardiac arrhythmias** (wide QRS), and **CNS depression/seizures**. - It does **not cause the massive elevation in liver enzymes** noted in this patient. *Opiate ingestion* - Presents with a classic triad of **CNS depression, respiratory depression**, and **miosis (pinpoint pupils)**. - Liver enzyme derangements are **not a primary feature** of opiate overdose. *Salicylate ingestion* - Causes a complex acid-base disturbance, typically a **respiratory alkalosis** followed by a **metabolic acidosis**, and symptoms like **tinnitus** and **hyperthermia**. - While it can cause elevated liver enzymes, they are usually **not as dramatically high** as observed in this case.

Question 136: A 38-year-old woman comes to the physician for a follow-up examination. Two years ago, she was diagnosed with multiple sclerosis. Three weeks ago, she was admitted and treated for right lower leg weakness with high-dose methylprednisone for 5 days. She has had 4 exacerbations over the past 6 months. Current medications include interferon beta and a multivitamin. Her temperature is 37°C (98.6°F), pulse is 90/min, and blood pressure is 116/74 mm Hg. Examination shows pallor of the right optic disk. Neurologic examination shows no focal findings. She is anxious about the number of exacerbations and repeated hospitalizations. She is counseled about the second-line treatment options available to her. She consents to treatment with natalizumab. However, she has read online about its adverse effects and is concerned. This patient is at increased risk for which of the following complications?

A. Tuberculosis
B. Syndrome of inappropriate antidiuretic hormone
C. Parkinsonism
D. Progressive multifocal leukoencephalopathy (Correct Answer)
E. Aplastic anemia

Explanation: ***Progressive multifocal leukoencephalopathy*** - **Natalizumab** is a monoclonal antibody that blocks the binding of leukocytes to endothelial cells, preventing their entry into the central nervous system. This immunosuppressive effect increases the risk of **progressive multifocal leukoencephalopathy (PML)**, especially in patients who are positive for the **JC virus**. - PML is a serious and often fatal opportunistic infection of the brain caused by the **JC virus**, which demyelinates axons and leads to severe neurological deficits. *Tuberculosis* - While some immunosuppressants can reactivate **latent tuberculosis**, natalizumab is not typically associated with an increased risk of TB compared to other immunomodulatory drugs like TNF-alpha inhibitors. - The mechanism of action of natalizumab (alpha-4 integrin blocker) does not directly impede the immune response responsible for containing mycobacterial infections to the same extent as other treatments. *Syndrome of inappropriate antidiuretic hormone* - **SIADH** is not a known adverse effect of natalizumab. - SIADH is characterized by excessive secretion of **antidiuretic hormone**, leading to hyponatremia, and is often associated with certain medications (e.g., SSRIs, carbamazepine) or underlying conditions like malignancy or pulmonary disease. *Parkinsonism* - Parkinsonism involves symptoms like **bradykinesia**, rigidity, and tremor, and is a neurodegenerative disorder. - There is **no evidence** suggesting a causal link between natalizumab treatment and the development of Parkinsonism. *Aplastic anemia* - **Aplastic anemia** is a rare but severe condition where the bone marrow fails to produce blood cells. - This adverse effect is not associated with natalizumab; it is more commonly linked to certain **chemotherapeutic agents**, radiation, or specific antimicrobial drugs like chloramphenicol.

Question 137: A 5-year-old boy is brought to the emergency room lapsing in and out of consciousness. The mother reports that 30 minutes ago, the young boy was found exiting the garage severely confused. A container of freshly spilled antifreeze was found on the garage floor. The next appropriate step would be to administer:

A. Fomepizole (Correct Answer)
B. Ammonium chloride
C. Flumazenil
D. Dimercaprol
E. N-acetylcysteine

Explanation: ***Fomepizole*** - The presentation of a child found near spilled **antifreeze** (ethylene glycol) who is lapsing in and out of consciousness strongly suggests **ethylene glycol poisoning**. - **Fomepizole** acts as a competitive inhibitor of **alcohol dehydrogenase**, preventing the metabolism of ethylene glycol into toxic metabolites like **glycolic acid** and **oxalic acid**, which cause metabolic acidosis and organ damage. *Ammonium chloride* - **Ammonium chloride** is an **acidifying agent** that is used in certain metabolic alkalosis cases or for urinary acidification to enhance excretion of basic drugs. - It is not indicated for **ethylene glycol poisoning** and could worsen the existing metabolic acidosis that typically develops in such cases. *Flumazenil* - **Flumazenil** is a **benzodiazepine receptor antagonist** used to reverse the effects of benzodiazepine overdose. - The patient's symptoms are not consistent with **benzodiazepine overdose**, and flumazenil would have no therapeutic effect in **ethylene glycol poisoning**. *Dimercaprol* - **Dimercaprol** (BAL) is a **chelating agent** primarily used to treat poisoning by heavy metals such as arsenic, mercury, and lead. - It has no role in the treatment of **ethylene glycol poisoning**, which involves metabolic disruption rather than heavy metal toxicity. *N-acetylcysteine* - **N-acetylcysteine** (NAC) is an antidote primarily used for **acetaminophen overdose**, where it replenishes glutathione stores to detoxify toxic acetaminophen metabolites. - It is not effective in treating **ethylene glycol poisoning**, as the mechanism of toxicity and the antidote's action are entirely different.

Question 138: An experimental infusable drug, X729, is currently being studied to determine its pharmacokinetics. The drug was found to have a half life of 1.5 hours and is eliminated by first order kinetics. What is the minimum number of hours required to reach a steady state concentration of >90%?

A. 6 (Correct Answer)
B. 3
C. 7.5
D. 1.5
E. 4.5

Explanation: ***6*** - For a drug eliminated by **first-order kinetics**, approximately **4 to 5 half-lives** are required to reach **steady-state concentration**. - To reach >90% of steady-state, at least **4 half-lives** are needed, where **93.75%** of the steady state is achieved. - The time taken would be **4 half-lives × 1.5 hours/half-life = 6 hours**, making this the **minimum time** to exceed 90%. *3* - This represents only **2 half-lives** (2 × 1.5 hours = 3 hours), which would achieve roughly **75%** of the steady-state concentration. - This is insufficient to reach >90% of the steady-state concentration. *7.5* - This time point represents **5 half-lives** (5 × 1.5 hours = 7.5 hours), which would achieve approximately **97%** of the steady-state concentration. - While this does exceed 90%, the question asks for the **minimum** number of hours required, and 90% is already exceeded at 6 hours (4 half-lives). *1.5* - This is only **1 half-life**, which would achieve approximately **50%** of the steady-state concentration. - This is far too early to reach a >90% steady-state concentration. *4.5* - This represents **3 half-lives** (3 × 1.5 hours = 4.5 hours), achieving approximately **87.5%** of the steady-state concentration. - While close to 90%, it does not quite reach "greater than 90%".

Question 139: A 2-year-old boy is brought to the physician for generalized fatigue and multiple episodes of abdominal pain and vomiting for the past week. His last bowel movement was 4 days ago. He has been having behavioral problems at home for the past few weeks as well. He can walk up stairs with support and build a tower of 3 blocks. He cannot use a fork. He does not follow simple instructions and speaks in single words. His family emigrated from Bangladesh 6 months ago. He is at the 40th percentile for height and weight. His temperature is 37°C (98.6°F), pulse is 115/min, and blood pressure is 84/45 mm Hg. Examination shows pale conjunctivae and gingival hyperpigmentation. His hemoglobin concentration is 10.1 g/dL, mean corpuscular volume is 68 μm3, and mean corpuscular hemoglobin is 24.5 pg/cell. The patient is most likely going to benefit from administration of which of the following?

A. Vitamin B12 and folate
B. Penicillamine
C. Iron
D. Thiosulfate and hydroxocobalamin
E. Succimer and calcium disodium edetate (Correct Answer)

Explanation: ***Succimer and calcium disodium edetate*** - This patient presents with symptoms such as **abdominal pain**, **vomiting**, **constipation**, **generalized fatigue**, and **behavioral problems**, along with **gingival hyperpigmentation** and **microcytic anemia** (Hb 10.1 g/dL, MCV 68 μm3, MCH 24.5 pg/cell). These are classic signs of **lead poisoning**. - **Succimer (DMSA)** and **calcium disodium edetate (CaNa2EDTA)** are chelation therapies used to treat lead poisoning by binding to lead and promoting its excretion. They are indicated for elevated blood lead levels, especially in symptomatic children. *Vitamin B12 and folate* - These are given for **megaloblastic anemia**, characterized by **macrocytic red blood cells** (high MCV), which is not seen here as the MCV is low (68 μm3). - Symptoms of B12 deficiency (e.g., neurological deficits, glossitis) and folate deficiency (e.g., fatigue, megaloblastic changes) are distinct from the patient's presentation. *Penicillamine* - **Penicillamine** is a chelating agent primarily used for **Wilson's disease** (copper overload) or **cystinuria**. - While it has some chelating properties for heavy metals, it is not the first-line or most effective treatment for lead poisoning and has a different side-effect profile. *Iron* - **Iron supplementation** is used to treat **iron deficiency anemia**, a common cause of microcytic anemia. However, the patient's constellation of symptoms, including neurological and gastrointestinal issues, and gingival hyperpigmentation, strongly points away from simple iron deficiency as the primary diagnosis. - Giving iron in the presence of lead poisoning without addressing lead can mask the underlying issue and not resolve the more systemic effects. *Thiosulfate and hydroxocobalamin* - **Sodium thiosulfate** and **hydroxocobalamin** are antidotes used for **cyanide poisoning**. - The patient's symptoms are inconsistent with cyanide exposure, which typically involves rapid onset of severe metabolic acidosis, cardiovascular collapse, and respiratory arrest.

Question 140: An experimental drug, ES 62, is being studied. It prohibits the growth of vancomycin-resistant Staphylococcus aureus. It is highly lipid-soluble. The experimental design is dependent on a certain plasma concentration of the drug. The target plasma concentration is 100 mmol/dL. Which of the following factors is most important for calculating the appropriate loading dose?

A. Volume of distribution (Correct Answer)
B. Half-life of the drug
C. Therapeutic index
D. Clearance of the drug
E. Rate of administration

Explanation: **Volume of distribution** - The **loading dose** is primarily determined by the desired **plasma concentration** and the **volume of distribution (Vd)**, as it reflects how extensively a drug is distributed in the body. - The formula for loading dose is: Loading Dose = (Target Plasma Concentration × Vd). *Half-life of the drug* - The **half-life** is crucial for determining the **dosing interval** and the time it takes to reach **steady-state concentrations**, not the initial loading dose. - It reflects the rate at which the drug is eliminated from the body. *Therapeutic index* - The **therapeutic index** is a measure of a drug's relative safety, indicating the ratio between the **toxic dose** and the **effective dose**. - While important for drug safety, it does not directly determine the magnitude of the loading dose itself. *Clearance of the drug* - **Clearance** is the rate at which the drug is removed from the body and is a primary determinant of the **maintenance dose** required to sustain a desired plasma concentration. - It does not directly calculate the initial loading dose needed to achieve an immediate target concentration. *Rate of administration* - The **rate of administration** (e.g., infusion rate) primarily influences how quickly the drug reaches its target concentration, but not the total quantity of drug needed for the initial loading dose. - It affects the kinetics of how the loading dose achieves the target concentration, rather than defining the dose amount.

Question 141: A 33-year-old man with recently diagnosed testicular cancer visits his oncologist to discuss the treatment plan. His left testicle was removed after a thorough workup of a lump. A pelvic CT showed no enlarged lymph nodes and a simple orchiectomy and pelvic lymph node dissection was completed. The final diagnosis was stage IB non-seminoma testicular cancer (pT2N0M0). A combination of different chemotherapeutic medications is recommended including bleomycin, etoposide, and cisplatin. Each of the antineoplastic drugs has a different mechanism of action targeting cancer cells. What is the primary mechanism of action of bleomycin in cancer treatment?

A. Direct DNA strand cleavage (Correct Answer)
B. Ribonucleotide reductase inhibition
C. RNA polymerase inhibition
D. Topoisomerase II inhibition
E. DNA polymerase inhibition

Explanation: ***Direct DNA strand cleavage*** - Bleomycin is a **cytotoxic antibiotic** that induces DNA damage by generating **free radicals**, leading to **single and double-strand DNA breaks**. - This mechanism primarily occurs in the **G2 and M phases** of the cell cycle, inhibiting DNA synthesis and cell division. *Ribonucleotide reductase inhibition* - This is the primary mechanism of action for drugs like **hydroxyurea**, which prevents the conversion of **ribonucleotides to deoxyribonucleotides**, thereby impairing DNA synthesis. - Bleomycin does not act by inhibiting this enzyme. *RNA polymerase inhibition* - This mechanism is associated with drugs such as **dactinomycin (actinomycin D)**, which intercalates into DNA and blocks RNA synthesis. - Bleomycin's action is more direct in causing DNA damage rather than inhibiting RNA transcription. *Topoisomerase II inhibition* - Drugs like **etoposide** and **doxorubicin** are topoisomerase II inhibitors, which prevent DNA unwinding and re-ligation, leading to DNA breaks and cell death. - While etoposide is used in the same regimen, this is not the mechanism of action for bleomycin. *DNA polymerase inhibition* - This is the mechanism of action for certain **antimetabolites** and **nucleoside analogs**, such as **cytarabine** or **gemcitabine**, which interfere with DNA replication by blocking DNA polymerase. - Bleomycin's action is distinct, involving direct oxidative cleavage of DNA.

Question 142: A 32-year-old man presents to an outpatient clinic for tuberculosis prophylaxis before leaving for a trip to Asia, where tuberculosis is endemic. The Mantoux test is positive, but the chest X-ray and AFB sputum culture are negative. He was started on isoniazid. What is the most likely mechanism of resistance to isoniazid?

A. Methylation of the RNA binding site
B. Plasmid-mediated resistance
C. Reduction of drug binding to RNA polymerase
D. Increased efflux from the cell
E. Mutations in katG (Correct Answer)

Explanation: ***Mutations in katG*** - The **katG gene** encodes **catalase-peroxidase**, an enzyme essential for activating isoniazid into its active form within *Mycobacterium tuberculosis*. - Mutations in *katG* prevent the activation of isoniazid, thereby conferring **resistance**. *Methylation of the RNA binding site* - This mechanism is primarily associated with **aminoglycoside resistance**, where methylation of ribosomal RNA prevents antibiotic binding. - It is not a known mechanism for resistance to **isoniazid**. *Plasmid-mediated resistance* - While common in many bacteria for antibiotic resistance, **plasmid-mediated resistance** is rare for **first-line anti-tuberculosis drugs** like isoniazid in *Mycobacterium tuberculosis*. - Most *M. tuberculosis* resistance mechanisms involve **chromosomal mutations**. *Reduction of drug binding to RNA polymerase* - This mechanism is typically associated with resistance to **rifamycins** (e.g., rifampin), which target the **bacterial RNA polymerase**. - Isoniazid's mechanism of action involves **mycolic acid synthesis inhibition**, not RNA polymerase binding. *Increased efflux from the cell* - While efflux pumps contribute to antibiotic resistance in many bacteria, they are less commonly the primary mechanism for high-level **isoniazid resistance** in *M. tuberculosis*. - Resistance is predominantly linked to target modification or enzyme deficits, like those involving **katG**.

Question 143: A 55-year-old man with a history of hypertension and benign prostate hyperplasia presents for follow-up 4 days into the treatment of a urinary tract infection with trimethoprim-sulfamethoxazole. His symptoms have resolved, and he reports no problems with urination, with the exception of a weak urine stream and hesitancy, which he has had for the past 2 years. At the time of this visit, the patient is afebrile; the blood pressure is 130/88 mm Hg and the heart rate is 80/min. There is no flank tenderness. A urinalysis reveals no leukocytes and is negative for esterase. The urinalysis reveals 2 red blood cells (RBCs)/ high power field (HPF), and there are no casts on urinary sediment analysis. The physician, however, notices the following abnormality: Prior treatment BUN 12 mg/dL Creatinine 1.2 mg/dL Today’s visit BUN 13 mg/dL Creatinine 2.1 mg/dL

A. Admit the patient for further management of acute interstitial nephritis
B. Admit the patient for further management of acute tubular necrosis
C. Schedule a cystoscopy for urethral obstruction
D. Schedule an intravenous pyelography for urinary obstruction
E. Reassure the patient, stop trimethoprim-sulfamethoxazole and repeat the measurement in 1–2 weeks (Correct Answer)

Explanation: ***Reassure the patient, stop trimethoprim-sulfamethoxazole and repeat the measurement in 1–2 weeks*** - The patient's **creatinine elevation** from 1.2 to 2.1 mg/dL after starting **trimethoprim-sulfamethoxazole** is likely due to the drug's known effect of inhibiting **creatinine secretion** in the renal tubules, leading to a rise in serum creatinine without actual kidney injury, and this effect is often reversible upon discontinuation. - Given that the patient's symptoms of UTI have resolved, and there are no signs of active kidney injury (afebrile, no flank tenderness, normal urinalysis for leukocytes/casts, mild RBCs), the most appropriate step is to stop the medication and monitor kidney function. *Admit the patient for further management of acute interstitial nephritis* - **Acute interstitial nephritis** typically presents with systemic symptoms like **fever**, **rash**, and **eosinophilia**, none of which are present in this case. - The urinalysis would typically show **white blood cells** and possibly **eosinophils**, which are absent here. *Admit the patient for further management of acute tubular necrosis* - **Acute tubular necrosis** (ATN) usually causes a more significant and rapid rise in creatinine, often accompanied by **oliguria** or **anuria**, and a urinalysis showing muddy brown casts, which are not seen here. - The patient's symptoms have improved, suggesting no severe acute kidney injury requiring admission for ATN. *Schedule a cystoscopy for urethral obstruction* - While the patient has a history of benign prostatic hyperplasia (BPH) and symptoms of weak stream and hesitancy, these are chronic issues and do not explain the acute rise in creatinine. - A **cystoscopy** is an invasive procedure and is not indicated as an immediate response to this reversible creatinine elevation. *Schedule an intravenous pyelography for urinary obstruction* - An **intravenous pyelography** (IVP) is used to visualize the urinary tract and might detect a urinary obstruction, but the history of BPH and chronic symptoms don't point towards a new, acute obstructive process causing the creatinine increase. - Furthermore, an IVP involves contrast dye, which could be nephrotoxic, especially in a patient with elevated creatinine, making it an inappropriate initial step.

Question 144: A 56-year-old woman undergoes open reduction and internal fixation of the distal tibia 1 day after a fall. She has had rheumatoid arthritis for 12 years and diabetes mellitus for 2 years. Her medications over the past year have included metformin, prednisone, calcium supplements, and methotrexate. Prior to surgery, insulin was added to her medications, and the dose of prednisone was increased. She has had appropriate nutrition over the years with regular follow-ups with her healthcare professional. Which of the following is the most appropriate supplement to prevent wound failure in this patient?

A. Glutamine
B. Zinc
C. Vitamin A
D. Arginine
E. Vitamin C (Correct Answer)

Explanation: ***Vitamin C*** - This patient is at high risk for **wound healing complications** due to her comorbidities (diabetes, rheumatoid arthritis) and medications (prednisone, methotrexate). **Vitamin C** (ascorbic acid) is essential for **collagen synthesis** and cross-linking, which is crucial for wound strength and tissue repair. - While other options play a role in wound healing, Vitamin C is particularly important in patients with **impaired healing** due to chronic inflammation, corticosteroid use, and metabolic disorders, as it counteracts their negative effects on collagen formation. *Glutamine* - **Glutamine** is an important fuel for rapidly dividing cells, including immune cells and fibroblasts, and can be beneficial in catabolic states. - However, its role in directly counteracting the specific challenges of this patient's wound healing (corticosteroid use, diabetes, rheumatoid arthritis) is **less direct** compared to Vitamin C's role in collagen synthesis. *Zinc* - **Zinc** is a cofactor for numerous enzymes involved in cell proliferation, immune function, and collagen synthesis. - While important, zinc deficiency is not explicitly indicated, and its role as a primary intervention to prevent wound failure in a patient with **prednisone-induced healing impairment** is secondary to vitamin C. *Vitamin A* - **Vitamin A** can help reverse the negative effects of **corticosteroids** on wound healing by promoting epithelialization and collagen synthesis. - While relevant due to prednisone use, its overall importance in **collagen formation** and direct wound strength is not as profound or broad as Vitamin C. *Arginine* - **Arginine** is a precursor for nitric oxide, which improves blood flow to wounds, and is involved in collagen formation and immune function. - Although beneficial for wound healing, particularly in critically ill patients, it is **not the most appropriate single supplement** for addressing the specific collagen synthesis impairment seen in this patient's context of corticosteroid use and chronic disease.

Question 145: A 25-year-old woman presented to an urgent care center with a complaint of a cough for more than 3 weeks that was accompanied by night sweats, weight loss, and malaise. On physical examination, the patient had slightly pale palpebral conjunctivae, bilateral posterior cervical lymphadenopathy, but with no adventitious breath sounds in the lung fields bilaterally. The remainder of the physical examination was routine. The patient was started on a drug regimen that was to be taken for 6 months. On follow-up after 2 months, the ALT and AST levels were elevated. Which of the following anti-tubercular drugs could have contributed to this laboratory result?

A. Streptomycin
B. Rifampicin
C. Ethambutol
D. Isoniazid (Correct Answer)
E. Pyrazinamide

Explanation: ***Isoniazid*** - **Isoniazid** is the **most commonly implicated** anti-tubercular drug in hepatotoxicity, particularly in the first 2 months of therapy, which matches this patient's timeline. - While **Pyrazinamide** and **Rifampicin** can also cause hepatotoxicity, **Isoniazid** causes hepatotoxicity in **10-20% of patients** with elevated transaminases and is the **most frequent single agent** responsible for drug-induced liver injury in TB treatment. - The hepatotoxicity manifests as elevated **ALT and AST levels** and can range from mild, asymptomatic enzyme elevations to severe, fatal hepatitis. - Risk factors include **fast acetylator status**, alcohol use, and concurrent use of other hepatotoxic drugs. *Rifampicin* - **Rifampicin** can cause **hepatotoxicity**, but when it occurs alone (without Isoniazid), it typically presents as a **cholestatic pattern** with elevated alkaline phosphatase and bilirubin rather than predominantly elevated transaminases. - Its primary adverse effects include **red-orange discoloration** of bodily fluids and significant drug interactions due to potent **cytochrome P450 enzyme induction**. - Hepatotoxicity from Rifampicin is **less common** than from Isoniazid when used as monotherapy. *Pyrazinamide* - **Pyrazinamide** can cause **hepatotoxicity** and is associated with elevated liver enzymes, making it a possible contributor. - However, **hepatotoxicity from Pyrazinamide** is **dose-dependent** and typically seen more with higher doses (>30 mg/kg/day) or in patients with pre-existing liver disease. - It is also associated with **hyperuricemia** and can precipitate gouty arthritis, which is not indicated in this clinical scenario. - In standard first-line therapy, **Isoniazid remains statistically more likely** to cause isolated transaminase elevation. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily known for its **ototoxicity** (vestibular and cochlear damage) and **nephrotoxicity**, rather than hepatotoxicity. - Liver enzyme elevation is **not a characteristic adverse effect** of streptomycin and is rarely reported. *Ethambutol* - **Ethambutol** is primarily associated with **optic neuritis**, leading to decreased visual acuity and red-green color blindness, which requires monitoring with regular visual acuity and color vision testing. - While mild liver enzyme elevations can rarely occur, significant **hepatotoxicity is uncommon** and not a characteristic primary adverse effect of ethambutol.

Question 146: A 24-year-old man presents to his primary care provider with complaints of 2 days of profuse diarrhea. He states that his stool started to turn watery and lighter in color beginning yesterday, and he has not noticed any fevers. His diarrhea episodes have become more frequent and white-colored over the past day. He has also noticed dry mouth symptoms and darker urine today. He is otherwise healthy but recently returned from a trip with friends to South Asia. None of his friends have reported any symptoms. On exam, his temperature is 98.6°F (37.0°C), blood pressure is 110/68 mmHg, pulse is 80/min, respirations are 14/min. The patient has normal skin turgor, but he has noticeably dry oral mucosa and chapped lips. The patient has dull abdominal aching but no tenderness to palpation. The stool is found to contain large quantities of comma-shaped organisms. Fecal occult blood testing is negative and no steatorrhea is found. The provider recommends immediate oral rehydration therapy. Which of the following is the likely mechanism of this patient’s diarrhea?

A. Decreased cyclic AMP
B. Inhibition of protein synthesis
C. Increased cyclic AMP (Correct Answer)
D. Shortening of intestinal villi
E. Increased cyclic GMP

Explanation: ***Increased cyclic AMP*** - The clinical picture of **watery, white-colored "rice-water" diarrhea** without fever, rapid onset following travel to South Asia, and the presence of **comma-shaped organisms** strongly points to **Vibrio cholerae** infection. - The **cholera toxin** produced by *V. cholerae* permanently **activates adenylate cyclase**, leading to persistently **increased intracellular cyclic AMP (cAMP)** levels within intestinal epithelial cells, causing massive secretion of chloride and water into the lumen. *Decreased cyclic AMP* - This mechanism would typically lead to **decreased fluid secretion** into the intestinal lumen, likely resulting in constipation or less severe diarrhea, which is contrary to the patient's presentation of profuse watery diarrhea. - **Decreased cyclic AMP** is not a known mechanism for the severe secretory diarrhea caused by pathogens like *Vibrio cholerae*. *Inhibition of protein synthesis* - Toxins that inhibit protein synthesis, such as **Shiga toxin** from *Shigella dysenteriae* or Shiga-like toxin from **enterohemorrhagic E. coli (EHEC)**, cause **cytotoxicity** and mucosal damage, often leading to **bloody diarrhea (dysentery)**. - The patient's diarrhea is watery and lacks blood, making this mechanism less likely. *Shortening of intestinal villi* - **Villous atrophy** or shortening of intestinal villi **reduces the absorptive surface area** and can lead to malabsorptive diarrhea. - While this can cause watery diarrhea, it typically doesn't result in the extreme volume and "rice-water" appearance characteristic of cholera, nor is it the primary mechanism of action for *Vibrio cholerae* toxins. *Increased cyclic GMP* - Some bacterial toxins, such as **heat-stable enterotoxins (STa)** produced by **enterotoxigenic E. coli (ETEC)**, increase **intracellular cyclic GMP (cGMP)**, leading to chloride and water secretion. - While ETEC can cause watery diarrhea, *Vibrio cholerae* specifically acts via **cAMP**, and the classic "rice-water" stools are more indicative of cholera.

Question 147: A 19-year-old woman presents to the emergency department with chronic diarrhea, fatigue, and weakness. She also had mild lower extremity edema. On examination, she was noted to be pale. Blood testing revealed peripheral eosinophilia (60%) and a Hb concentration of 8 g/dL. The stool examination revealed Fasciolopsis buski eggs. Which of the following drugs would most likely be effective?

A. Albendazole
B. Oxamniquine
C. Niclosamide
D. Praziquantel (Correct Answer)
E. Bithionol

Explanation: ***Praziquantel*** - **Praziquantel** is the **drug of choice** for treating trematode infections, including those caused by **Fasciolopsis buski**. - Its mechanism of action involves increasing the permeability of the parasite's cell membrane to calcium, leading to paralysis and death of the fluke. - It is highly effective, well-tolerated, and the standard first-line treatment. *Albendazole* - **Albendazole** is primarily used for various **nematode (roundworm)** infections, such as ascariasis, hookworm, and trichuriasis. - While it has some activity against certain cestodes, it is not the first-line treatment for **Fasciolopsis buski**, a **trematode (fluke)**. *Oxamniquine* - **Oxamniquine** is an anthelmintic specifically used for the treatment of **schistosomiasis**, particularly against *Schistosoma mansoni*. - It works by damaging the adult worms' teguments, but it is not effective against **Fasciolopsis buski**. *Niclosamide* - **Niclosamide** is an effective treatment for **cestode (tapeworm)** infections, such as *Taenia saginata* and *Hymenolepis nana*. - Its mechanism involves inhibiting parasitic mitochondrial oxidative phosphorylation, but it is not active against **fluke** infections like **Fasciolopsis buski**. *Bithionol* - **Bithionol** is used primarily for treating **Fasciola hepatica** (the common liver fluke) and **Paragonimus westermani** (lung fluke) infections. - While it has trematocidal activity, it is **not the drug of choice** for **Fasciolopsis buski**—**praziquantel** is preferred due to its superior efficacy, broader spectrum against intestinal flukes, better safety profile, and widespread availability.

Question 148: A 31-year-old man comes to the physician because of several months of recurrent abdominal pain and diarrhea. Six months ago, he traveled to Lake Superior for a fishing trip with his friends, during which they often ate their day's catch for dinner. Physical examination shows pallor. Laboratory studies show macrocytic anemia with eosinophilia. A peripheral blood smear shows megaloblasts and hypersegmented neutrophils. A cestode infection is suspected and a drug is prescribed that kills cestodes by inducing uncontrollable muscle spasm in the parasite. The drug prescribed for this patient most likely acts by which of the following mechanisms of action?

A. Increased calcium influx into the sarcoplasm (Correct Answer)
B. Increased potassium efflux from the sarcoplasm
C. Increased sodium efflux from the sarcoplasm
D. Phosphorylation of adenosine diphosphate
E. Blockade of myosin binding sites

Explanation: ***Increased calcium influx into the sarcoplasm*** - The clinical picture (macrocytic anemia, eosinophilia, travel history, eating raw fish) points to **Diphyllobothriasis**, caused by the **fish tapeworm** *Diphyllobothrium latum*. - The drug described, causing **uncontrollable muscle spasm**, is likely **Praziquantel**, which works by increasing **calcium influx** into the worms, leading to paralysis and dislodgement. *Increased potassium efflux from the sarcoplasm* - This mechanism is not characteristic of anti-cestode medications that induce muscle spasms. - While ion channels are therapeutic targets, **potassium efflux** wouldn't directly lead to spastic paralysis in this context. *Increased sodium efflux from the sarcoplasm* - This mechanism is not typically associated with the anti-cestode drug Praziquantel or other drugs causing spastic paralysis in parasites. - Changes in **sodium concentrations** can affect muscle function, but not in the described manner for cestodes. *Phosphorylation of adenosine diphosphate* - This refers to the formation of ATP and is a fundamental process in cellular energy metabolism, not a direct drug mechanism for inducing muscle spasms in parasites. - Anti-parasitic drugs usually target specific metabolic pathways or ion channels rather than general energy production in this manner. *Blockade of myosin binding sites* - This mechanism would typically lead to muscle relaxation or flaccid paralysis (e.g., botulinum toxin in humans), not the spastic, uncontrollable spasms described. - Drugs that block **myosin binding** prevent muscle contraction, which is the opposite of the described effect.

Question 149: A 60-year-old female presents to her gynecologist with bloating, abdominal discomfort, and fatigue. She has a history of hypertension and takes hydrochlorothiazide. Physical exam reveals ascites and right adnexal tenderness. Initial imaging reveals a mass in the right ovary and eventual biopsy of the mass reveals ovarian serous cystadenocarcinoma. She is started on a chemotherapeutic agent with plans for surgical resection. Soon after starting the medication, she develops dysuria and hematuria. Laboratory analysis of her urine is notable for the presence of a cytotoxic metabolite. Which of the following mechanisms of action is consistent with the medication in question?

A. Folate analog
B. Microtubule inhibitor
C. DNA alkylating agent (Correct Answer)
D. Platinum-based DNA cross-linking agent
E. BRAF inhibitor

Explanation: ***DNA alkylating agent*** - Cyclophosphamide is a **DNA alkylating agent** commonly used in the treatment of ovarian cancer. It is metabolized to **acrolein**, a cytotoxic metabolite that causes **hemorrhagic cystitis**, presenting as dysuria and hematuria. - DNA alkylating agents exert their cytotoxic effects by forming **covalent bonds** with DNA, leading to DNA damage, cross-linking, and subsequent inhibition of DNA replication and transcription, ultimately inducing **apoptosis** in rapidly dividing cancer cells. *Folate analog* - Folate analogs like **methotrexate** inhibit **dihydrofolate reductase**, interfering with DNA synthesis by depleting tetrahydrofolate, a crucial cofactor for nucleotide synthesis. - While they are chemotherapeutic agents, they do not typically cause hemorrhagic cystitis; their common side effects include **myelosuppression**, mucositis, and hepatotoxicity. *Microtubule inhibitor* - Microtubule inhibitors such as **paclitaxel** and **vincristine** interfere with microtubule formation or breakdown, disrupting cell division (mitosis). - Common side effects include **neuropathy** and myelosuppression, but not hemorrhagic cystitis. *Platinum-based DNA cross-linking agent* - Platinum-based drugs like **cisplatin** and **carboplatin** are often used for ovarian cancer and cause nephrotoxicity, neurotoxicity, and ototoxicity. - They form **DNA adducts and interstrand cross-links**, inhibiting DNA replication and transcription, but do not directly cause acrolein-induced hemorrhagic cystitis. *BRAF inhibitor* - BRAF inhibitors (e.g., **vemurafenib**) are **targeted therapies** used in cancers with specific mutations, such as BRAF-mutated melanoma. - They inhibit the BRAF kinase in the MAPK signaling pathway, and while effective in specific contexts, they are not typically associated with hemorrhagic cystitis.

Question 150: A 71-year-old man with asthma and dementia presents to the emergency department in acute respiratory distress. He is with his home care nurse who explains that he has been hiding his bronchodilators for the past 3 weeks, and she has had to dutifully look for them and help him administer them. Over the past 2 days, however, she has been completely unsuccessful in finding his medication and was in the process of contacting his primary care physician for a refill of his prescription when he suddenly had a ‘coughing fit’ and began wheezing uncontrollably. The patient is obviously uncomfortable and is using accessory muscles of respiration to catch his breath. He is struggling to speak and is immediately given multiple doses of nebulized albuterol and intravenous methylprednisolone; however, his condition does not improve. The arterial blood gas test result shows pH 7.20. He is subsequently intubated and sent to the intensive care unit (ICU). In patients who are intubated for mechanical ventilation, there is an increased risk for ventilator-associated pneumonia. Which of the following should be prophylactically given to this patient to lower his risk for pneumonia?

A. Sucralfate (Correct Answer)
B. Clarithromycin
C. Omeprazole
D. Ceftazidime
E. Famotidine

Explanation: ***Correct: Sucralfate*** - **Sucralfate is the preferred agent for stress ulcer prophylaxis** when prevention of ventilator-associated pneumonia (VAP) is a priority in mechanically ventilated patients. - Unlike acid-suppressing agents, sucralfate **does not alter gastric pH**, which means it prevents bacterial overgrowth in the stomach that can be aspirated into the lungs. - Multiple meta-analyses have shown that sucralfate is associated with a **lower risk of VAP** compared to proton pump inhibitors (PPIs) and H2 receptor blockers. - It forms a protective barrier over gastric and duodenal ulcers without raising gastric pH, thereby maintaining the stomach's natural antimicrobial defense. *Incorrect: Omeprazole* - Omeprazole is a **proton pump inhibitor (PPI)** that significantly reduces gastric acid production and raises gastric pH. - While effective for stress ulcer prophylaxis, **PPIs are associated with an increased risk of VAP** (approximately 20-30% increased risk). - The elevated gastric pH promotes bacterial colonization and overgrowth, which can be aspirated into the respiratory tract. - Current guidelines recommend **avoiding routine PPI use** in mechanically ventilated patients when VAP prevention is a concern. *Incorrect: Famotidine* - Famotidine is an **H2 receptor blocker** that reduces gastric acid secretion. - Like PPIs, **H2 blockers increase the risk of VAP** by raising gastric pH and allowing bacterial overgrowth. - While famotidine can be used for stress ulcer prophylaxis, it is **not the preferred choice** when VAP prevention is the primary concern. - Studies show similar VAP risk increases with H2 blockers as with PPIs. *Incorrect: Clarithromycin* - Clarithromycin is a macrolide antibiotic with no role in **prophylaxis against VAP**. - Routine prophylactic antibiotic use in intubated patients is **not recommended** due to concerns about antimicrobial resistance. - Antibiotics should be reserved for documented infections, not routine prevention in all mechanically ventilated patients. *Incorrect: Ceftazidime* - Ceftazidime is a third-generation cephalosporin antibiotic with activity against **Pseudomonas aeruginosa**. - It is used for **treatment** of established infections, not for routine prophylaxis against VAP. - Prophylactic antibiotic use promotes **antibiotic resistance** and is not standard practice for VAP prevention in all intubated patients.

Question 151: A 52-year-old man presents to his primary care physician because he has been experiencing shortness of breath and cough. He began feeling short of breath when playing recreational soccer with his friends. Over time these episodes have become more severe. They now impair his ability to work as a construction worker. In addition, he has developed a chronic dry cough that has been increasing in intensity. Radiography reveals subpleural cystic enlargement, and biopsy reveals fibroblast proliferation in the affected tissues. Which of the following describes the mechanism of action for a drug that can cause a similar pattern of pulmonary function testing as would be seen in this disease?

A. Pyrimidine analogue
B. Microtubule inhibitor
C. Purine analogue
D. Dihydrofolate reductase inhibitor (Correct Answer)
E. Xanthine oxidase inhibitor

Explanation: ***Dihydrofolate reductase inhibitor*** - The patient's symptoms (shortness of breath, dry cough, subpleural cystic enlargement, fibroblast proliferation) are consistent with **pulmonary fibrosis**, which presents as a **restrictive lung disease**. - **Methotrexate**, a **dihydrofolate reductase inhibitor**, is a known cause of drug-induced pulmonary fibrosis, leading to a restrictive pattern on pulmonary function tests. *Pyrimidine analogue* - **Pyrimidine analogues** like **gemcitabine** or **5-fluorouracil** are primarily chemotherapy agents and are not strongly associated with pulmonary fibrosis. - Their mechanisms typically involve interrupting DNA or RNA synthesis, and while they can have pulmonary side effects, fibrosis is not their characteristic pattern. *Microtubule inhibitor* - **Microtubule inhibitors** such as **paclitaxel** or **vincristine** are antineoplastic drugs commonly used in cancer treatment. - While they can cause various side effects, including neurotoxicity and myelosuppression, **pulmonary fibrosis** is not a common or characteristic adverse effect. *Purine analogue* - **Purine analogues** like **azathioprine** or **cladribine** are immunosuppressants and chemotherapeutic agents. - Although these drugs can have pulmonary toxicity, they are less commonly associated with significant **pulmonary fibrosis** compared to methotrexate. *Xanthine oxidase inhibitor* - **Xanthine oxidase inhibitors**, such as **allopurinol** and **febuxostat**, are primarily used to treat **gout** by reducing uric acid production. - Pulmonary side effects, particularly **pulmonary fibrosis**, are exceedingly rare with this class of drugs.

Question 152: A 64-year-old woman comes to the physician because of a 7-month history of abdominal discomfort, fatigue, and a 6.8-kg (15-lb) weight loss. Physical examination shows generalized pallor and splenomegaly. Laboratory studies show anemia with pronounced leukocytosis and thrombocytosis. Cytogenetic analysis shows a BCR-ABL fusion gene. A drug with which of the following mechanisms of action is most appropriate for this patient?

A. Ribonucleotide reductase inhibitor
B. Monoclonal anti-HER-2 antibody
C. Topoisomerase II inhibitor
D. Monoclonal anti-CD20 antibody
E. Tyrosine kinase inhibitor (Correct Answer)

Explanation: ***Tyrosine kinase inhibitor*** - The patient's symptoms (abdominal discomfort, fatigue, weight loss, pallor, splenomegaly), laboratory findings (**anemia with pronounced leukocytosis and thrombocytosis**), and the presence of a **BCR-ABL fusion gene** are highly characteristic of **Chronic Myeloid Leukemia (CML)**. - The **BCR-ABL fusion gene** encodes a constitutively active **tyrosine kinase**, which is the hallmark of CML and the primary therapeutic target for **tyrosine kinase inhibitors (TKIs)** like imatinib. *Ribonucleotide reductase inhibitor* - **Ribonucleotide reductase inhibitors** (e.g., hydroxyurea) block DNA synthesis and are used in myeloproliferative disorders to reduce cell counts, but they are not specific to the **BCR-ABL fusion gene** and are not the most appropriate first-line targeted therapy for CML. - While they can control symptoms, they do not target the underlying molecular defect in CML as effectively as TKIs. *Monoclonal anti-HER-2 antibody* - **Monoclonal anti-HER-2 antibodies** (e.g., trastuzumab) are used to treat **HER-2 positive breast cancer** and some gastric cancers. - They are not relevant to the treatment of CML, which is characterized by the **BCR-ABL fusion gene**. *Topoisomerase II inhibitor* - **Topoisomerase II inhibitors** (e.g., etoposide, doxorubicin) prevent DNA unwinding and replication, leading to cell death, and are used in various hematologic malignancies and solid tumors. - These drugs are broad-spectrum chemotherapeutic agents not specifically targeted to the **BCR-ABL fusion protein** in CML and are not first-line therapy for this condition. *Monoclonal anti-CD20 antibody* - **Monoclonal anti-CD20 antibodies** (e.g., rituximab) target the CD20 protein on B lymphocytes and are primarily used to treat **B-cell non-Hodgkin lymphoma** and some autoimmune diseases. - They have no role in the direct treatment of CML, which is a myeloid malignancy.

Question 153: An 18-month-old boy is brought to the physician because of walking difficulties. His mother says that he cannot walk unless he is supported. She has also noted orange, sandy residues in his diapers. Over the past year, she has frequently caught him pulling his toenails and chewing the tips of his fingers. Examination shows scarring of his fingertips. Muscle tone is decreased in the upper and lower extremities. He cannot pick up and hold small objects between the tips of the index finger and the thumb. The most appropriate pharmacotherapy for this patient's condition inhibits which of the following conversions?

A. Hypoxanthine to inosine monophosphate
B. Adenosine to inosine
C. Ornithine to citrulline
D. Orotate to uridine monophosphate
E. Xanthine to urate (Correct Answer)

Explanation: ***Xanthine to urate*** - The patient's symptoms (developmental delay, self-mutilation, hypotonia, orange sandy residues in diapers) are classic for **Lesch-Nyhan syndrome**, which is caused by a deficiency of **hypoxanthine-guanine phosphoribosyltransferase (HGPRT)**. - This deficiency leads to increased production of uric acid; the most appropriate pharmacotherapy is **allopurinol**, which inhibits **xanthine oxidase**, thereby blocking the conversion of xanthine to urate and reducing uric acid levels. *Hypoxanthine to inosine monophosphate* - This conversion is part of the **salvage pathway** catalyzed by **HGPRT**, which is deficient in Lesch-Nyhan syndrome. - Inhibiting this step would worsen the underlying deficiency and is not a therapeutic strategy for this condition. *Adenosine to inosine* - This conversion is catalyzed by **adenosine deaminase (ADA)**. A deficiency in ADA leads to **severe combined immunodeficiency (SCID)**, not Lesch-Nyhan syndrome. - While ADA deficiency involves purine metabolism, its clinical presentation and treatment are distinct. *Ornithine to citrulline* - This step is part of the **urea cycle**, catalyzed by **ornithine transcarbamylase (OTC)**. - Deficiency in OTC results in **hyperammonemia** and neurological symptoms, but not the specific features of Lesch-Nyhan syndrome like self-mutilation or hyperuricemia. *Orotate to uridine monophosphate* - This conversion is involved in **pyrimidine synthesis**, catalyzed by **uridine monophosphate synthase**. - A defect in this pathway leads to **orotic aciduria**, characterized by megaloblastic anemia and growth retardation, which is different from the presentation of Lesch-Nyhan syndrome.

Question 154: A 60-year-old man is rushed to the emergency room after he was found unconscious in bed that afternoon. The patient’s wife says he has been confused and irritable for the past several days. She says he has a history of chronic daily alcohol abuse and has been hospitalized multiple times with similar symptoms His temperature is 37°C (98.6°F), the blood pressure is 110/80 mm Hg, the pulse is 90/min, and the respiratory rate is 14/min. On physical examination, the patient is minimally responsive to painful stimuli. His abdomen is distended with positive shifting dullness. Laboratory results are as follows: Complete blood count Hematocrit 35% Platelets 100,000/mm3 White blood cells 5000/mm3 Liver function studies Serum Albumin 2 g/dL Alkaline phosphatase (ALP) 200 IU/L Aspartate aminotransferase (AST) 106 IU/L Alanine aminotransferase (ALT) 56 IU/L The patient is admitted to the hospital and started on the appropriate treatment to improve his mental status. Which of the following best describes the mechanism of action of the drug that is most likely used to treat this patient’s symptoms?

A. Prevents the conversion of ammonia into ammonium
B. Increases ammonia production and absorption
C. Increases pH in the gastrointestinal lumen
D. Decreases pH in the gastrointestinal lumen (Correct Answer)
E. Decreases the colonic concentration of bacteria

Explanation: ***Decreases pH in the gastrointestinal lumen*** - The patient's presentation with altered mental status, chronic alcohol abuse, distended abdomen with shifting dullness (*ascites*), and abnormal liver function tests (low *albumin*, elevated *AST/ALT*) is highly suggestive of **hepatic encephalopathy**. - **Lactulose** is the mainstay treatment for hepatic encephalopathy, and its mechanism involves lowering the colonic pH, which converts ammonia (NH3) into poorly absorbed ammonium (NH4+), thereby reducing systemic ammonia levels. *Prevents the conversion of ammonia into ammonium* - This statement is incorrect; the goal of treatment for hepatic encephalopathy is to **promote** the conversion of ammonia to ammonium to prevent its absorption. - Ammonia (NH3) is lipophilic and readily crosses the blood-brain barrier, while ammonium (NH4+) is hydrophilic and poorly absorbed from the gut. *Increases ammonia production and absorption* - This is incorrect and would exacerbate hepatic encephalopathy by increasing the toxic ammonia load. - The primary aim of treatment is to **reduce** ammonia production and enhance its excretion or conversion into a non-absorbable form. *Increases pH in the gastrointestinal lumen* - Elevating the pH in the colon would favor the production of **ammonia (NH3)** from ammonium (NH4+), leading to increased systemic ammonia absorption and worsening hepatic encephalopathy. - Therefore, this mechanism would be detrimental to a patient with hepatic encephalopathy. *Decreases the colonic concentration of bacteria* - While **rifaximin** (a non-absorbable antibiotic) does decrease ammonia-producing bacteria in the gut and is used in conjunction with lactulose, this option describes the mechanism of an antibiotic, not the primary action of lactulose. - Lactulose itself does not primarily decrease the overall concentration of gut bacteria, but rather modifies the *metabolic activity* of the existing bacteria.

Question 155: A 25-year-old man presents with abdominal pain and bloody diarrhea. His symptoms have been recurrent for the past few months, and, currently, he says he is having on average four bowel movements daily, often bloody. He describes the pain as cramping and localized to the left side of his abdomen. He also says that he has lost around 4.5 kg (10 lb) over the past 3 months. There is no other significant past medical history and the patient is not on current medications. His temperature is 37.7° C (100.0° F), pulse rate is 100/min, respiratory rate is 18/min, and blood pressure is 123/85 mm Hg. On physical examination, there is mild tenderness to palpation in the lower left quadrant of the abdomen with no rebound or guarding. Laboratory studies show anemia and thrombocytosis. Colonoscopy is performed, which confirms the diagnosis of ulcerative colitis (UC). What is the mechanism of action of the recommended first-line medication for the treatment of this patient’s condition?

A. Suppression of cellular and humoral immunity
B. TNF-⍺ antagonism
C. Inhibition of enzyme phospholipase A2
D. Cross-linking of bacterial DNA
E. Inhibition of leukotriene synthesis and lipoxygenase (Correct Answer)

Explanation: ***Inhibition of leukotriene synthesis and lipoxygenase*** - The first-line medications for mild to moderate ulcerative colitis (UC) are **aminosalicylates** like **mesalamine** (5-ASA). - Mesalamine is thought to exert its anti-inflammatory effects by inhibiting **leukotriene synthesis** and the **lipoxygenase pathway**, thereby reducing inflammation in the colon. *Suppression of cellular and humoral immunity* - This mechanism of action describes **immunosuppressants** such as azathioprine or methotrexate, which are typically used for more severe or refractory cases of UC, not as first-line therapy. - These drugs broadly suppress the immune system, leading to a higher risk of infections and other side effects. *TNF-⍺ antagonism* - This is the mechanism of action of **biologic agents** like infliximab or adalimumab, which are reserved for moderate to severe UC that has not responded to conventional therapy. - **TNF-α inhibitors** block the inflammatory cytokine TNF-α, reducing inflammation but are not the initial treatment choice. *Inhibition of enzyme phospholipase A2* - This mechanism describes **corticosteroids** such as prednisone or budesonide, which are used to induce remission in moderate to severe UC flares, but not as first-line maintenance therapy due to significant side effects. - Corticosteroids inhibit **phospholipase A2**, thereby blocking the entire arachidonic acid cascade and the production of all inflammatory mediators. *Cross-linking of bacterial DNA* - This mechanism describes **antibiotics** like metronidazole or ciprofloxacin, which work by cross-linking DNA in bacteria. - While antibiotics may be used in specific UC scenarios (such as pouchitis or suspected superimposed infection), UC itself is an idiopathic inflammatory disease, not a bacterial infection, and antibiotics are not first-line treatment for the underlying condition.

Question 156: A 46-year-old male presents to his dermatologist for routine follow-up of his psoriasis. He was last seen in the office six months prior, at which time he started undergoing ultraviolet light therapy. He reports that he initially noticed an improvement in his symptoms but the effects were transient. He has also started noticing pain and stiffness in his fingers. His past medical history is notable for obesity and diabetes mellitus. He takes metformin. His temperature is 99°F (37.2°C), blood pressure is 130/80 mmHg, pulse is 80/min, and respirations are 16/min. Multiple plaques with scaling are noted on the extensor surfaces of the upper and lower extremities. The patient’s physician suggests stopping the ultraviolet light therapy and starting an injectable medication that acts as a decoy receptor for a pro-inflammatory cytokine. Which of the following is an adverse effect associated with the use of this medication?

A. Cushing’s syndrome
B. Retinopathy
C. Myelosuppression
D. Reactivation of latent tuberculosis (Correct Answer)
E. Nephrotoxicity

Explanation: ***Reactivation of latent tuberculosis*** - The patient's symptoms (psoriasis with associated arthralgias) suggest **psoriatic arthritis**. The physician's recommendation for an injectable medication acting as a decoy receptor for a **pro-inflammatory cytokine** refers to a **TNF-α inhibitor** (e.g., etanercept, infliximab, adalimumab). - TNF-α inhibitors suppress the immune system, making patients susceptible to **opportunistic infections**, including the **reactivation of latent tuberculosis** (TB). Screening for latent TB is crucial before initiating these medications. *Cushing’s syndrome* - **Cushing's syndrome** is caused by prolonged exposure to high levels of **glucocorticoids**, either endogenous (e.g., adrenal tumors) or exogenous (e.g., long-term steroid use). - TNF-α inhibitors do not directly cause Cushing's syndrome; they are **biologic agents** that target specific inflammatory pathways. *Retinopathy* - **Retinopathy** is a condition affecting the retina, often associated with systemic diseases like **diabetes** or medications such as **hydroxychloroquine**. - TNF-α inhibitors are not typically associated with retinopathy as a direct side effect. *Myelosuppression* - **Myelosuppression** (bone marrow suppression) is a common adverse effect of **chemotherapeutic agents** and some immunosuppressants (e.g., methotrexate, azathioprine). - While TNF-α inhibitors can rarely cause hematologic abnormalities, significant myelosuppression is not a characteristic or common adverse effect compared to traditional cytotoxic drugs. *Nephrotoxicity* - **Nephrotoxicity** refers to kidney damage caused by drugs, such as **NSAIDs**, aminoglycosides, or certain chemotherapeutic agents. - TNF-α inhibitors are not primarily associated with nephrotoxicity as a significant adverse effect.

Question 157: An 8-year-old boy is brought to the emergency department by his parents because of sudden onset of abdominal pain beginning an hour ago. The parents report that their son has also had an episode of dark urine earlier that morning. Three days ago, he was diagnosed with a urinary tract infection and was treated with trimethoprim-sulfamethoxazole. He emigrated from Liberia to the US with his family 3 years ago. There is no personal history of serious illness. His immunizations are up-to-date. Vital signs are within normal limits. Examination shows diffuse abdominal tenderness and scleral icterus. The spleen is palpated 1–2 cm below the left costal margin. Laboratory studies show: Hemoglobin 10 g/dL Mean corpuscular volume 90 μm3 Reticulocyte count 3% Serum Bilirubin Total 3 mg/dL Direct 0.5 mg/dL Haptoglobin 20 mg/dL (N=41–165 mg/dL) Lactate dehydrogenase 160 U/L Urine Blood 3+ Protein 1+ RBC 2–3/hpf WBC 2–3/hpf Which of the following is the most likely underlying cause of this patient's symptoms?

A. Production of hemoglobin S
B. Deficient glucose-6-phosphate dehydrogenase (Correct Answer)
C. Lead poisoning
D. Cold agglutinins
E. Defective RBC membrane proteins

Explanation: ***Deficient glucose-6-phosphate dehydrogenase*** - The patient's presentation with **hemolytic anemia** (low hemoglobin, elevated reticulocytes, low haptoglobin, elevated LDH, elevated indirect bilirubin) following **trimethoprim-sulfamethoxazole** administration, along with dark urine (hemoglobinuria), is highly suggestive of G6PD deficiency. - G6PD deficiency is common in individuals of African descent (patient emigrated from Liberia) and certain medications like sulfa drugs can trigger **oxidative stress** leading to hemolysis in affected individuals. *Production of hemoglobin S* - While **sickle cell anemia** (due to hemoglobin S) can cause hemolytic anemia and abdominal pain (**vaso-occlusive crisis**), the sudden onset linked to a specific medication and the absence of a prior history of serious illness make G6PD deficiency more likely. - Sickle cell disease typically presents with recurrent painful crises, dactylitis in infancy, and chronic hemolytic anemia, which are not described here. *Lead poisoning* - **Lead poisoning** can cause abdominal pain and anemia, but it typically presents with a **microcytic hypochromic anemia** and **basophilic stippling** on peripheral smear. - It does not directly cause an acute hemolytic crisis triggered by trimethoprim-sulfamethoxazole. *Cold agglutinins* - **Cold agglutinin disease** involves hemolytic anemia triggered by cold exposure, and the antibodies react optimally at cold temperatures. - The patient's symptoms are acute and triggered by a medication known to induce oxidative stress, which is not characteristic of cold agglutinin disease. *Defective RBC membrane proteins* - **Hereditary spherocytosis** (a defect in RBC membrane proteins like spectrin or ankyrin) causes chronic hemolytic anemia and splenomegaly. - While it can manifest with jaundice, it typically does not cause an acute, drug-induced hemolytic crisis with hemoglobinuria as seen here.

Question 158: A 45-year-old male presents to his primary care doctor complaining of abdominal pain. He reports a three-month history of intermittent burning pain localized to the epigastrium that worsens 2-3 hours after a meal. He attributes this pain to increased stress at his job. He is otherwise healthy and takes no medications. He does not smoke or drink alcohol. His temperature is 98.8°F (37.1°C), blood pressure is 130/85 mmHg, pulse is 90/min, and respirations are 18/min. Physical examination reveals mild epigastric tenderness to palpation. A urease breath test is positive. Which of the following treatments is most appropriate first-line therapy for this patient?

A. Octreotide
B. Sulfasalazine
C. Amoxicillin, clarithromycin, and omeprazole (Correct Answer)
D. Tetracycline, omeprazole, bismuth, and metronidazole
E. Pantoprazole

Explanation: ***Amoxicillin, clarithromycin, and omeprazole*** - The patient's symptoms (epigastric burning pain worsening 2-3 hours after meals) and a **positive urease breath test** strongly suggest a *Helicobacter pylori* infection causing a peptic ulcer or gastritis. - The standard first-line eradication therapy for *H. pylori* is **triple therapy**, which typically includes a **proton pump inhibitor (PPI)** like omeprazole and two antibiotics, usually **amoxicillin** and **clarithromycin**. *Octreotide* - **Octreotide** is a somatostatin analog used primarily for conditions causing excessive hormone secretion, such as **variceal bleeding**, neuroendocrine tumors (e.g., carcinoid syndrome, VIPomas), and acromegaly. - It is not indicated for the treatment of *H. pylori* infection or peptic ulcer disease in this context. *Sulfasalazine* - **Sulfasalazine** is an anti-inflammatory drug primarily used in the management of **inflammatory bowel disease (IBD)**, such as ulcerative colitis and Crohn's disease, and some forms of rheumatoid arthritis. - It has no role in the eradication of *H. pylori* or the treatment of peptic ulcer disease. *Tetracycline, omeprazole, bismuth, and metronidazole* - This combination, known as **quadruple therapy**, is primarily used as **second-line treatment** for *H. pylori* eradication, especially in cases of **treatment failure** with triple therapy or in areas with **high clarithromycin resistance**. - While effective, it's not the initial first-line approach when there's no known resistance or prior treatment failure. *Pantoprazole* - **Pantoprazole** is a proton pump inhibitor (PPI) that reduces gastric acid secretion and would alleviate the patient's symptoms. - However, using a PPI alone would only suppress symptoms and **would not eradicate the underlying *H. pylori* infection**, allowing the infection and potential ulceration to persist.

Question 159: A 47-year-old woman comes to the physician because of easy bruising and fatigue. She appears pale. Her temperature is 38°C (100.4°F). Examination shows a palm-sized hematoma on her left leg. Abdominal examination shows an enlarged liver and spleen. Her hemoglobin concentration is 9.5 g/dL, leukocyte count is 12,300/mm3, platelet count is 55,000/mm3, and fibrinogen concentration is 120 mg/dL (N = 150–400). Cytogenetic analysis of leukocytes shows a reciprocal translocation of chromosomes 15 and 17. Which of the following is the most appropriate treatment for this patient at this time?

A. Cyclophosphamide
B. All-trans retinoic acid (Correct Answer)
C. Imatinib
D. Rituximab
E. Platelet transfusion

Explanation: ***All-trans retinoic acid*** - This patient's presentation with **easy bruising, fatigue, pallor, fever, hepatosplenomegaly, thrombocytopenia**, and a **t(15;17) translocation** is highly characteristic of **acute promyelocytic leukemia (APL)**. - **All-trans retinoic acid (ATRA)** is the cornerstone of APL treatment, inducing differentiation of leukemic promyelocytes and reversing the coagulopathy often associated with this subtype. *Cyclophosphamide* - **Cyclophosphamide** is an alkylating agent used in various cancers and autoimmune diseases, but it is **not the primary or most appropriate initial therapy for APL**. - Its mechanism of action involves DNA damage, which is different from the differentiation-inducing effect needed for APL. *Imatinib* - **Imatinib** is a tyrosine kinase inhibitor primarily used for **chronic myeloid leukemia (CML)** and some GISTs, targeting the **BCR-ABL fusion protein**. - It is **ineffective in APL** as the underlying genetic abnormality (PML-RARA fusion) is different. *Rituximab* - **Rituximab** is a monoclonal antibody targeting the **CD20 antigen** found on B-lymphocytes, primarily used for **B-cell non-Hodgkin lymphoma** and some autoimmune conditions. - It has **no role in the treatment of acute promyelocytic leukemia**, which is a myeloid malignancy. *Platelet transfusion* - While the patient has **thrombocytopenia (platelet count 55,000/mm3)** and **easy bruising/hematoma**, suggesting a need for platelet support, it is a **supportive measure**, not the definitive treatment for the underlying disease. - **Platelet transfusion** alone does not address the fundamental pathophysiology of APL or the associated coagulopathy (fibrinogen 120 mg/dL), which requires ATRA.

Question 160: A 51-year-old woman presents to her primary care doctor with diarrhea. She has had 3-10 malodorous and loose bowel movements daily for the last 6 months, though she recalls that her bowel movements started increasing in frequency nearly 2 years ago. She was otherwise healthy until 2 years ago, when she had multiple elevated fasting blood glucose levels and was diagnosed with type 2 diabetes mellitus. She was also hospitalized once 6 months ago for epigastric pain that was determined to be due to cholelithiasis. She is an avid runner and runs 3-4 marathons per year. She is a vegetarian and takes all appropriate supplements. Her body mass index is 19 kg/m^2. She has lost 10 pounds since her last visit 18 months ago. On exam, she has dry mucous membranes and decreased skin turgor. A high-resolution spiral computerized tomography scan demonstrates a 5-cm enhancing lesion in the head of the pancreas. Additional similar lesions are found in the liver. Further laboratory workup confirms the diagnosis. The patient is offered surgery but refuses as she reportedly had a severe complication from anesthesia as a child. This patient should be treated with a combination of octreotide, 5-fluorouracil, and which other medication?

A. Paclitaxel
B. Glucagon
C. Streptozotocin (Correct Answer)
D. Insulin
E. Methotrexate

Explanation: ***Streptozotocin*** - The patient's presentation with **diarrhea**, **weight loss**, **new-onset diabetes**, and a **pancreatic mass with liver metastases** is highly suggestive of a **neuroendocrine tumor**, specifically a **VIPoma** or **gastrinoma** with potential for glucagonoma given the diabetes. Given the recommended treatment with octreotide and 5-fluorouracil, **streptozotocin** is a key cytotoxic chemotherapy agent used in the treatment of metastatic pancreatic neuroendocrine tumors. - **Streptozotocin** is an **alkylating agent** that targets pancreatic islet cells and is effective in combination with 5-fluorouracil for advanced, well-differentiated neuroendocrine tumors, especially those that are functional and causing symptoms. *Paclitaxel* - **Paclitaxel** is a **microtubule inhibitor** primarily used in breast, ovarian, and lung cancers. It is not a standard chemotherapy agent for pancreatic neuroendocrine tumors in combination with octreotide and 5-fluorouracil. - While sometimes used in other pancreatic malignancies (e.g., pancreatic adenocarcinoma), it is **not indicated** for the specific context of this neuroendocrine tumor treatment regimen. *Glucagon* - **Glucagon** is a hormone that **raises blood glucose levels** and would be contraindicated in a patient with new-onset diabetes and a pancreatic tumor, potentially exacerbating hyperglycemia. - It is a **hormone**, not a chemotherapy agent, and has no role in treating the underlying pancreatic neuroendocrine tumor. *Insulin* - **Insulin** treats hyperglycemia, which is a symptom in this patient due to likely a **glucagonoma** or other neuroendocrine tumor affecting glucose metabolism. However, it does not treat the underlying tumor. - While necessary for managing diabetes, **insulin** is a supportive treatment and not the chemotherapy agent required to combine with octreotide and 5-fluorouracil for directly targeting the tumor. *Methotrexate* - **Methotrexate** is an **antimetabolite** primarily used in various cancers like leukemia, lymphoma, and autoimmune diseases. It is not part of the standard chemotherapy regimen for pancreatic neuroendocrine tumors. - Its mechanism of action and efficacy profile do not align with the treatment of well-differentiated metastatic pancreatic neuroendocrine tumors in this context.

Question 161: An investigator is studying the genetic profile of an isolated pathogen that proliferates within macrophages. The pathogen contains sulfatide on the surface of its cell wall to prevent fusion of the phagosome and lysosome. She finds that some of the organisms under investigation have mutations in a gene that encodes the enzyme required for synthesis of RNA from a DNA template. The mutations are most likely to reduce the therapeutic effect of which of the following drugs?

A. Pyrazinamide
B. Ethambutol
C. Rifampin (Correct Answer)
D. Streptomycin
E. Levofloxacin

Explanation: ***Rifampin*** - **Rifampin** specifically targets bacterial **DNA-dependent RNA polymerase**, inhibiting **RNA synthesis**. Mutations in the gene encoding this enzyme would directly reduce rifampin's binding and effectiveness. - The description of the pathogen thriving within macrophages and using **sulfatide to evade lysosomal fusion** strongly suggests **Mycobacterium tuberculosis**, a bacterium for which rifampin is a cornerstone treatment. *Pyrazinamide* - **Pyrazinamide** is a prodrug that, once converted to **pyrazinoid acid**, disrupts **mycobacterial membrane potential** and metabolism. Its primary target is not RNA synthesis. - Its efficacy is pH-dependent and it acts optimally in acidic environments, such as within macrophages, but mutations affecting RNA synthesis would not directly compromise its action. *Ethambutol* - **Ethambutol** inhibits **arabinosyl transferase**, an enzyme essential for the synthesis of the **mycobacterial cell wall component arabinogalactan**. - Its mechanism of action is distinct from RNA synthesis, thus mutations affecting RNA polymerase would not impact its efficacy. *Streptomycin* - **Streptomycin** is an **aminoglycoside antibiotic** that binds to the **30S ribosomal subunit**, inhibiting bacterial **protein synthesis**. - This mechanism is unrelated to DNA-dependent RNA polymerase, so mutations in RNA synthesis enzymes would not affect streptomycin's action. *Levofloxacin* - **Levofloxacin** is a **fluoroquinolone antibiotic** that inhibits **bacterial DNA gyrase (topoisomerase II)** and **topoisomerase IV**, thereby blocking DNA replication and transcription. - While it affects processes related to DNA, its direct target is not the DNA-dependent RNA polymerase enzyme itself, distinguishing it from rifampin's specific mechanism.

Question 162: A 23-year-old woman on prednisone for lupus presents to her primary care physician because she experiences a burning sensation with urination. She has also been urinating more frequently than normal. The patient denies fever, chills, nausea/vomiting, abdominal or back pain, or other changes with urination. Her vital signs and physical exam are unremarkable, and her urine analysis is positive for leukocyte esterase and nitrites. The patient receives a diagnosis and is then prescribed an antimicrobial that acts by inhibiting DNA gyrase. Which adverse effect should the patient be counseled about?

A. Facial redness/flushing
B. Tendon rupture (Correct Answer)
C. Rhabdomyolysis
D. Hemolytic anemia
E. Leukopenia

Explanation: ***Tendon rupture*** - The patient's symptoms (dysuria, frequent urination, positive leukocyte esterase, and nitrites) are consistent with a **urinary tract infection (UTI)**. The antimicrobial that inhibits **DNA gyrase** is a **fluoroquinolone**, and a well-known adverse effect of fluoroquinolones is **tendon rupture**. - Risk factors for tendon rupture with fluoroquinolones include older age, corticosteroid use, and renal insufficiency, all of which are pertinent to this patient on **prednisone** for lupus. *Facial redness/flushing* - This is an adverse effect more commonly associated with drugs like **niacin** or calcium channel blockers, not fluoroquinolones. - It is generally not a recognized side effect of antibiotics used to treat UTIs. *Rhabdomyolysis* - This serious condition involves the breakdown of muscle tissue and is associated with various drugs (e.g., statins, street drugs) and conditions (e.g., trauma, extreme exertion), but not typically fluoroquinolones. - While muscle pain can occur with fluoroquinolones, severe rhabdomyolysis is rare. *Hemolytic anemia* - Certain antibiotics, like sulfonamides or penicillin, can rarely cause drug-induced hemolytic anemia, particularly in patients with **G6PD deficiency**. - Fluoroquinolones are not commonly associated with hemolytic anemia. *Leukopenia* - While some antibiotics can cause bone marrow suppression leading to leukopenia (e.g., chloramphenicol, trimethoprim-sulfamethoxazole), this is not a common or significant adverse effect of fluoroquinolones. - The patient's underlying lupus and prednisone use might contribute to immune dysregulation, but leukopenia is not the primary concern with fluoroquinolone use.

Question 163: A 21-year-old male presents after several days of flatulence and greasy, foul-smelling diarrhea. The patient reports symptoms of nausea and abdominal cramps followed by sudden diarrhea. He says that his symptoms started after he came back from a camping trip. When asked about his camping activities, he reports that his friend collected water from a stream, but he did not boil or chemically treat the water. His temperature is 98.6°F (37°C), respiratory rate is 15/min, pulse is 67/min, and blood pressure is 122/98 mm Hg. Stool is sent for microscopy which returns positive for motile protozoans. Which of the following antibiotics should be started in this patient?

A. Vancomycin
B. Erythromycin
C. Cephalexin
D. Ciprofloxacin
E. Metronidazole (Correct Answer)

Explanation: ***Metronidazole*** - This patient's symptoms (greasy, foul-smelling diarrhea, flatulence) after consuming untreated stream water are highly suggestive of **Giardiasis**, caused by *Giardia lamblia*. - **Metronidazole** is the first-line antibiotic for treating Giardiasis due to its efficacy against anaerobic parasites and protozoa. *Vancomycin* - **Vancomycin** is primarily used for serious gram-positive bacterial infections, particularly **methicillin-resistant *Staphylococcus aureus* (MRSA)** and *Clostridioides difficile* colitis. - It has no activity against protozoal infections like Giardiasis. *Erythromycin* - **Erythromycin** is a macrolide antibiotic effective against a range of bacterial infections, including atypical pneumonia and certain sexually transmitted infections. - It is not effective against protozoal parasites. *Cephalexin* - **Cephalexin** is a first-generation cephalosporin antibiotic used to treat bacterial infections such as skin and soft tissue infections, strep throat, and urinary tract infections. - It does not have activity against protozoans. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic used for various bacterial infections, including urinary tract infections, gastrointestinal infections (e.g., traveler's diarrhea caused by bacteria), and respiratory tract infections. - While effective against many bacteria, it is not the primary treatment for protozoal infections like Giardiasis.

Question 164: The patient is admitted to the hospital. A stereotactic brain biopsy of the suspicious lesion is performed that shows many large lymphocytes with irregular nuclei. Which of the following is the most appropriate treatment?

A. Methotrexate (Correct Answer)
B. Pyrimethamine and sulfadiazine
C. Intrathecal glucocorticoids
D. Surgical resection
E. Temozolomide

Explanation: ***Methotrexate*** - A brain biopsy showing **large lymphocytes with irregular nuclei** is highly suggestive of **primary central nervous system lymphoma (PCNSL)**. High-dose methotrexate is the cornerstone of PCNSL treatment due to its ability to cross the **blood-brain barrier** effectively. - Methotrexate is a **folate antagonist** that inhibits DNA synthesis, making it effective against rapidly dividing cancer cells, including lymphoma cells in the brain. *Pyrimethamine and sulfadiazine* - This combination is the standard treatment for **cerebral toxoplasmosis**, an opportunistic infection often seen in immunocompromised patients, which can present as a brain lesion. - However, the biopsy finding of **lymphoma cells** rules out toxoplasmosis as the primary diagnosis, making this treatment inappropriate. *Intrathecal glucocorticoids* - **Glucocorticoids** can be used to reduce **peritumoral edema** and provide symptomatic relief in PCNSL, but they are not a definitive treatment for the lymphoma itself. - While sometimes used as an adjunct, high-dose glucocorticoids can induce **lymphoma cell apoptosis**, potentially confounding diagnostic biopsy results if administered before the biopsy. *Surgical resection* - **Gross total resection** is generally not feasible or recommended for PCNSL because these tumors tend to be multifocal and deeply infiltrating, making complete removal difficult and often associated with significant neurological morbidity. - The primary treatment for PCNSL is **chemotherapy** (especially high-dose methotrexate) and sometimes radiation, rather than surgery. *Temozolomide* - **Temozolomide** is an **oral alkylating agent** primarily used in the treatment of **glioblastoma multiforme** and anaplastic astrocytoma, as well as other high-grade gliomas. - While it can cross the blood-brain barrier, it is not the primary or most effective chemotherapy for PCNSL, which responds better to methotrexate-based regimens.

Question 165: A 55-year-old man presents to his primary care physician for diarrhea. He states that he has experienced roughly 10 episodes of non-bloody and watery diarrhea every day for the past 3 days. The patient has a past medical history of IV drug abuse and recently completed treatment for an abscess with cellulitis. His vitals are notable for a pulse of 105/min. Physical exam reveals diffuse abdominal discomfort with palpation but no focal tenderness. A rectal exam is within normal limits and is Guaiac negative. Which of the following is the best initial treatment for this patient?

A. Oral rehydration and discharge
B. Vancomycin (Correct Answer)
C. Clindamycin
D. Fidaxomicin
E. Metronidazole

Explanation: ***Vancomycin*** - This patient's recent **antibiotic exposure** (for abscess and cellulitis) combined with **watery diarrhea** (10 episodes/day) and tachycardia (pulse 105/min) strongly suggests **Clostridioides difficile infection (CDI)**. - **Oral vancomycin** (125 mg PO four times daily × 10 days) is a first-line treatment for initial CDI per current IDSA guidelines and remains the most commonly used agent in clinical practice. - While fidaxomicin is also first-line (and preferred by guidelines due to lower recurrence rates), vancomycin is more widely available, cost-effective, and equally effective for initial treatment, making it the best initial choice in most clinical settings. *Oral rehydration and discharge* - While **oral rehydration** is important for managing dehydration secondary to diarrhea, it is insufficient as the sole treatment given the high clinical suspicion for **CDI**. - CDI requires targeted antibiotic therapy; discharging with only supportive care risks disease progression, toxic megacolon, and potentially life-threatening complications. *Clindamycin* - **Clindamycin** is one of the antibiotics **most strongly associated** with causing **CDI** because it significantly disrupts normal colonic flora. - Administering clindamycin would worsen the suspected CDI and is absolutely contraindicated in this clinical scenario. *Fidaxomicin* - **Fidaxomicin** (200 mg PO twice daily × 10 days) is an excellent antibiotic for **CDI** and is actually recommended as first-line therapy alongside vancomycin in current IDSA guidelines. - It has advantages including **lower recurrence rates** and better microbiome preservation compared to vancomycin. - However, in practice, it is less commonly used as initial therapy due to **significantly higher cost** (often >$3,000 vs. <$100 for vancomycin) and more limited availability. - For exam purposes and typical clinical practice, **vancomycin remains the preferred first-line agent** for initial CDI treatment. *Metronidazole* - **Metronidazole** was previously a first-line treatment for **non-severe CDI**, but current IDSA guidelines (2018/2021) no longer recommend it as first-line therapy. - It has **inferior efficacy** compared to vancomycin and fidaxomicin and is now reserved only for situations where neither vancomycin nor fidaxomicin is available. - Studies have shown higher treatment failure rates and recurrence rates with metronidazole compared to vancomycin.

Question 166: A 21-year-old man presents to the office for a follow-up visit. He was recently diagnosed with type 1 diabetes mellitus after being hospitalized for diabetic ketoacidosis following a respiratory infection. He is here today to discuss treatment options available for his condition. The doctor mentions a recent study in which researchers have developed a new version of the insulin pump that appears efficacious in type 1 diabetics. They are currently comparing it to insulin injection therapy. This new pump is not yet available, but it looks very promising. At what stage of clinical trials is this current treatment most likely at?

A. Phase 0
B. Phase 2
C. Phase 3 (Correct Answer)
D. Phase 1
E. Phase 4

Explanation: ***Phase 3*** - **Phase 3 trials** involve large-scale studies comparing the new treatment to standard therapy or placebo, often across multiple centers. - The scenario describes a "new version of the insulin pump" being compared to "insulin injection therapy," indicating a definitive comparison for efficacy and safety against existing treatments. *Phase 0* - **Phase 0 trials** are exploratory, small-scale studies (10-15 subjects) using micro-doses to gather preliminary data on pharmacodynamics and pharmacokinetics, not efficacy comparisons. - They are typically conducted very early in drug development, examining if the drug behaves as expected in humans. *Phase 2* - **Phase 2 trials** evaluate the efficacy and further assess safety of a new treatment in a larger group of patients (tens to hundreds). - While they assess efficacy, they usually don't involve direct comparison with an established standard therapy on the scale implied by the question, which is typically reserved for Phase 3. *Phase 1* - **Phase 1 trials** primarily focus on safety, dosage, and side effects in a small group of healthy volunteers or patients with the condition (20-100 subjects). - These trials are not designed to assess a treatment's efficacy against an existing therapy. *Phase 4* - **Phase 4 trials** occur after a drug or device has been approved and marketed, focusing on long-term safety, effectiveness in diverse populations, and new indications. - The described pump "is not yet available," indicating it has not reached the market and thus is not in Phase 4.

Question 167: A 48-year-old woman presented to the hospital with a headache, intermittent fevers and chills, generalized arthralgias, excessive thirst, increased fluid intake, and a progressive rash that developed on her back. Three days before seeking evaluation at the hospital, she noticed a small, slightly raised lesion appearing like a spider or insect bite on her back, which she considered to be a scab covering the affected region. The patient's fever reached 39.4°C (102.9°F) 2 days before coming to the hospital, with an intensifying burning sensation on the affected site. When a family member examined the bite, it was noticed that the bump had transformed into a circular rash. The patient took over-the-counter ibuprofen for intense pain so she could sleep through the night. The day before her hospital visit, the patient felt exhausted but managed to complete a normal workday. On the day of the hospital visit, she awoke feeling very ill, with shooting joint pains, high fevers, and excessive thirst, which led to her to seek medical attention. On physical examination, her temperature was 40.1°C (104.2°F), and there was a large circular red rash with a bulls-eye appearance (17 × 19 cm in diameter) on her back. The rest of the physical examination was unremarkable. Her past medical and surgical histories were not significant apart from a history of anaphylaxis when taking a tetracycline. She recalled a walk in the woods 3 weeks before this exam but denied finding a tick or any other ectoparasite on her body. She denied any nutritional or inhalational allergies, although she emphasized that she is allergic to tetracyclines. Based on her symptoms, medical history, and physical examination findings, the attending physician decides to institute antimicrobial therapy immediately. Which antimicrobial drug did the physician prescribe?

A. Azithromycin
B. Amoxicillin (Correct Answer)
C. Erythromycin
D. Doxycycline
E. Cephalexin

Explanation: ***Amoxicillin*** - The patient presents with classic symptoms of **Lyme disease**, including a **bull's-eye rash (erythema migrans)**, fever, chills, headache, and arthralgias, following a possible tick exposure. - Since the patient has a history of **anaphylaxis to tetracyclines**, **amoxicillin** is an appropriate first-line treatment for early Lyme disease in cases where doxycycline is contraindicated, especially in adults. *Azithromycin* - While macrolides like azithromycin can be used in some cases of early Lyme disease, they are generally considered **less effective** than doxycycline, amoxicillin, or cefuroxime. - Its use is typically reserved for patients who cannot tolerate beta-lactams or tetracyclines, and it has shown **lower efficacy** in preventing late-stage manifestations. *Erythromycin* - Erythromycin, another macrolide, is **not recommended** as a first-line treatment for Lyme disease due to its **limited efficacy** against *Borrelia burgdorferi*. - Its use is generally **discouraged** due to higher rates of treatment failure and gastrointestinal side effects compared to other options. *Doxycycline* - **Doxycycline** is the **first-line treatment** for early Lyme disease in adults due to its high efficacy against *Borrelia burgdorferi* and its ability to penetrate various tissues. - However, it is **contraindicated** in this patient due to her history of **anaphylaxis to tetracyclines**. *Cephalexin* - **Cephalexin** is a first-generation cephalosporin and is **not effective** against *Borrelia burgdorferi*, the causative agent of Lyme disease. - Beta-lactams like **cefuroxime axetil** are effective for Lyme disease, but cephalexin specifically is **not recommended** for this condition.

Question 168: A 25-year-old man comes to the physician because of diarrhea, bloating, nausea, and vomiting for the past 3 days. He describes his stool as soft, frothy, and greasy. He denies seeing blood in stool. The patient went on a hiking trip last week and drank fresh water from the stream. Three months ago, he was on vacation with his family for 2 weeks in Brazil, where he tried many traditional dishes. He also had watery diarrhea and stomach cramping for 3 days during his visit there. He has no history of serious illness. He takes no medications. The patient appears dehydrated. His temperature is 37°C (98.6°F), blood pressure is 100/60 mm Hg, pulse is 80/min, and respirations are 12/min. Examination shows dry mucous membranes and diffuse abdominal tenderness. Microscopy of the stool reveals cysts. Which of the following is the most appropriate next step in management?

A. Supportive treatment only
B. Trimethoprim-sulfamethoxazole therapy
C. Ciprofloxacin therapy
D. Metronidazole therapy (Correct Answer)
E. Octreotide therapy

Explanation: ***Metronidazole therapy*** - The patient's symptoms (diarrhea, bloating, greasy stool) and history (drinking stream water, stool cysts) are highly suggestive of **Giardiasis**, for which **metronidazole** is the drug of choice. - The presence of **cysts in stool microscopy** confirms a parasitic infection, making antibiotic therapy targeting bacteria (like ciprofloxacin or trimethoprim-sulfamethoxazole) inappropriate. *Supportive treatment only* - While supportive care (rehydration) is important due to the patient's dehydration, it is **insufficient as the sole management** for Giardiasis given the persistent symptoms and confirmed parasitic infection. - Delaying specific antiparasitic treatment can lead to **chronic symptoms** and malabsorption. *Trimethoprim-sulfamethoxazole therapy* - This antibiotic is effective against certain **bacterial infections**, but it is generally *not* the first-line treatment for **Giardiasis**. - Its use would be more appropriate for specific bacterial diarrheas or other parasitic infections like *Cystoisospora* or *Cyclospora*. *Ciprofloxacin therapy* - **Ciprofloxacin** is a fluoroquinolone antibiotic primarily used for **bacterial diarrheas**, particularly those caused by *E. coli*, *Salmonella*, or *Shigella*. - It is **ineffective** against **Giardia** and would not treat the underlying parasitic infection. *Octreotide therapy* - **Octreotide** is a somatostatin analog used to treat **secretory diarrhea**, often associated with neuroendocrine tumors (e.g., VIPomas) or refractory diarrhea in AIDS patients. - It has **no role** in treating infectious parasitic diarrhea like **Giardiasis**.

Question 169: A 60-year-old man presents to the emergency department with shortness of breath, cough, and fever. He states that his symptoms started a few days ago and have been progressively worsening. The patient recently returned from international travel. He works from home and manages a chicken coop as a hobby. He has a past medical history of an ST-elevation myocardial infarction and recently has had multiple sick contacts. His temperature is 102°F (38.9°C), blood pressure is 187/108 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 93% on room air. A radiograph of the chest reveals bilateral pleural effusions. Pleurocentesis demonstrates the findings below: Protein ratio (pleural/serum): 0.8 Lactate dehydrogenase ratio (pleural/serum): 0.75 Glucose: 25 mg/dL Further analysis reveals a lymphocytic leukocytosis of the pleural fluid. Which of the following is the next best step in management?

A. Furosemide
B. Azithromycin and ceftriaxone
C. Supportive therapy
D. Azithromycin and vancomycin
E. Rifampin, isoniazid, pyrazinamide, and ethambutol (Correct Answer)

Explanation: ***Rifampin, isoniazid, pyrazinamide, and ethambutol*** - The patient's **pleural fluid analysis** (exudative effusion by Light's criteria, low glucose, and lymphocytic leukocytosis) with a history of **recent international travel** and sick contacts, and hobbies involving **chickens**, strongly suggests **tuberculous pleurisy**. - **Quadruple antituberculous therapy** is the appropriate initial management for active tuberculosis. *Furosemide* - This is a **diuretic** primarily used for conditions like **heart failure**, which causes **transudative effusions**. - The patient's pleural fluid is **exudative** (high protein and LDH ratios), making furosemide inappropriate. *Azithromycin and ceftriaxone* - These are common antibiotics for **community-acquired bacterial pneumonia**. - While the patient has respiratory symptoms, the **pleural fluid characteristics** (lymphocytic predominance, very low glucose) are not typical for uncomplicated bacterial pneumonia. *Supportive therapy* - While supportive care (oxygen, fluids) is always part of managing critically ill patients, it is **insufficient as the primary treatment** for a suspected active infectious process like tuberculosis. - Delaying specific treatment for tuberculosis can lead to **disease progression** and poorer outcomes. *Azithromycin and vancomycin* - This combination targets a broader spectrum of bacteria, including atypical pathogens and MRSA, often used in severe bacterial pneumonia or healthcare-associated infections. - However, the **pleural fluid characteristics** point away from typical bacterial causes and toward tuberculosis.

Question 170: A 26-year-old woman is brought to the emergency department after a suicide attempt. Her mother found her next to an empty bottle of acetaminophen in the bathroom. The patient reports that she ingested about twenty-five 500 mg pills. She took the pills 1 hour prior to arrival to the emergency department. She has a history of major depressive disorder. She does not smoke or use illicit drugs. Current medications include fluoxetine. She is oriented to person, place, and time. Vital signs are within normal limits. Physical examination shows no abnormalities. Laboratory studies show: Hemoglobin 12.5 g/dL Leukocyte count 8,000/mm3 Platelet count 150,000/mm3 Serum Prothrombin time 10.5 sec (INR=1.0) Na+ 141 mEq/L K+ 4.2 mEq/L Cl- 101 mEq/L HCO3- 25 mEq/L Urea nitrogen 10 g/dL Creatinine 0.5 g/dL Ca2+ 8.8 mg/dL Total bilirubin 0.4 mg/dL AST 22 U/L ALT 25 U/L Alkaline phosphatase 62 U/L Which of the following is the most appropriate next step in management?

A. Administer N-acetylcysteine (Correct Answer)
B. Admit for observation
C. Administer activated charcoal
D. List for liver transplant
E. Perform liver biopsy

Explanation: ***Administer N-acetylcysteine*** - The patient ingested a significant amount of **acetaminophen** (25 x 500 mg = 12,500 mg or 12.5 grams), which is a potentially fatal dose, necessitating immediate administration of **N-acetylcysteine (NAC)** as an antidote. - NAC replenishes **glutathione stores**, which helps detoxify the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI) and prevents **hepatic necrosis**. *Admit for observation* - While observation is part of the management, simply admitting for observation without administering **NAC** would be insufficient and potentially dangerous given the high dose of **acetaminophen** ingested. - The risk of **liver damage** is high with this dose; active treatment is required, not just monitoring. *Administer activated charcoal* - **Activated charcoal** is most effective when administered within **1-2 hours** of ingestion. Although the patient presented within 1 hour, **NAC** is the more critical intervention for **acetaminophen overdose** to prevent **hepatotoxicity**. - Activated charcoal's efficacy significantly decreases after 1 hour, and it does not directly prevent the toxic effects of acetaminophen on the liver, unlike NAC. *List for liver transplant* - **Liver transplant** is considered for **fulminant hepatic failure** unresponsive to medical management, indicated by severe coagulopathy, encephalopathy, and persistent metabolic acidosis, which are not present at this early stage. - Administering **NAC** promptly can prevent the progression to severe **liver damage** that would necessitate a transplant. *Perform liver biopsy* - A **liver biopsy** is an invasive procedure and is not indicated in the acute management of **acetaminophen overdose**. - Diagnostic information regarding liver damage (e.g., AST/ALT levels) can be obtained through less invasive blood tests, and the priority is to administer the antidote rather than perform a biopsy.

Question 171: A 45-year-old female who recently immigrated to the United States presents to the community health clinic for episodes of disrupted vision. She is concerned because she knows several people from her hometown who went blind after having these episodes. Over the past several months, she also has developed itchy bumps on her back and lower extremities. Physical exam reveals black hyperpigmented nodules with edema and palpable lymphadenopathy, but is otherwise unremarkable without any visible discharge from the eyes. Her physician explains her underlying disease was likely transmitted by black flies. Which of the following is the most appropriate pharmacotherapy for this patient?

A. Diethylcarbamazine
B. Ivermectin (Correct Answer)
C. Praziquantel
D. Mebendazole
E. Nifurtimox

Explanation: ***Ivermectin*** - This patient presents with symptoms characteristic of **onchocerciasis** (river blindness), including visual disturbances, itchy skin nodules, and transmission by **black flies**. - **Ivermectin** is the drug of choice for onchocerciasis as it effectively kills the **microfilariae** and reduces the adult worm burden. *Diethylcarbamazine* - While effective against some filarial infections, **diethylcarbamazine (DEC)** is contraindicated in onchocerciasis due to the risk of severe and potentially fatal **Mazzotti reaction**. - This reaction results from a rapid killing of microfilariae, leading to intense inflammation, bronchospasm, and hypotension. *Praziquantel* - **Praziquantel** is the drug of choice for treating **schistosomiasis** and **tapeworm infections**. - It has no activity against the filarial nematodes that cause onchocerciasis. *Mebendazole* - **Mebendazole** is an anthelminthic primarily used to treat intestinal nematode infections like **ascariasis**, **hookworm**, and **pinworm**. - It is not effective against onchocerciasis. *Nifurtimox* - **Nifurtimox** is the drug of choice for treating **Chagas disease** (American trypanosomiasis). - It has no role in the treatment of onchocerciasis.

Question 172: A 10-year-old girl is brought to the physician because of itching of the vulva and anal region for the past 2 weeks. She has difficulty sleeping because of the itching. Physical examination shows excoriation marks around the vulva and perianal region. There is minor perianal erythema, but no edema or fissures. Microscopy of an adhesive tape applied to the perianal region shows multiple ova. Which of the following is the most appropriate treatment for this patient?

A. Mebendazole (Correct Answer)
B. Diethylcarbamazine
C. Praziquantel
D. Nifurtimox
E. Melarsoprol

Explanation: ### ***Mebendazole*** * This patient's symptoms (perianal and vulvar itching, difficulty sleeping, excoriation marks) along with the finding of **ova on an adhesive tape test** are characteristic of **enterobiasis (pinworm infection)** caused by *Enterobius vermicularis*. * **Mebendazole** is an **effective and commonly used broad-spectrum anthelmintic for pinworm infections**, working by inhibiting microtubule synthesis in the worms. ### *Diethylcarbamazine* * **Diethylcarbamazine** is primarily used to treat **filariasis (e.g., lymphatic filariasis caused by *Wuchereria bancrofti* or *Brugia malayi*)** and **loiasis (*Loa loa*)**. * It is not indicated for the treatment of pinworm infection. ### *Praziquantel* * **Praziquantel** is the drug of choice for treating **schistosomiasis (bilharzia)** and most **cestode (tapeworm) infections**. * It works by increasing parasitic cell membrane permeability to calcium, causing paralysis and dislodgement of the worms, but it is not effective against pinworms. ### *Nifurtimox* * **Nifurtimox** is an antiprotozoal drug primarily used for the treatment of **Chagas disease** (American trypanosomiasis) caused by *Trypanosoma cruzi*. * It is not used for helminthic infections like pinworms. ### *Melarsoprol* * **Melarsoprol** is a highly toxic arsenic-containing drug reserved for the treatment of **late-stage (meningoencephalitic stage) African trypanosomiasis** (sleeping sickness) caused by *Trypanosoma brucei rhodesiense* and *gambiense*. * Its severe side effects make it unsuitable for common parasitic infections like pinworms.

Question 173: A 23-year-old woman visits her general practitioner with left ear pain and fever. She complains of multiple episodes of respiratory infection including bronchitis, laryngitis, and sinusitis. She was diagnosed with systemic lupus erythematosus with nephritis 8 months ago and was placed on oral prednisone. Currently, she takes prednisone daily. Her vital signs are as follows: blood pressure 130/85 mm Hg, heart rate 79/min, respiratory rate 16/min, and temperature 37.5°C (99.5°F). Her weight is 78 kg (172 lb) and height is 169 cm (5 ft 6 in). Physical examination reveals a swollen erythematous left eardrum, erythematous macular rash over sun-exposed skin, and slight calf edema. Inhibition of which of the following pathways causes diminished immune cell activation in this patient?

A. NF-κB pathway (Correct Answer)
B. PI3K/AKT/mTOR pathway
C. Notch pathway
D. Wnt pathway
E. Hippo pathway

Explanation: ***NF-κB pathway*** - This patient is on **prednisone**, a glucocorticoid, to manage her **systemic lupus erythematosus (SLE)**. Glucocorticoids exert their anti-inflammatory and immunosuppressive effects primarily by inhibiting the **NF-κB pathway**. - Inhibition of **NF-κB** prevents the transcription of pro-inflammatory genes, including those for **cytokines**, chemokines, and adhesion molecules, thereby diminishing immune cell activation and reducing inflammation. *PI3K/AKT/mTOR pathway* - This pathway is crucial for cell growth, proliferation, survival, and metabolism, and its dysregulation is often associated with cancer. - While it can influence immune cell function, it is **not the primary target** of glucocorticoids like prednisone in suppressing immune activation. *Notch pathway* - The **Notch pathway** is critical for cell-to-cell communication, regulating cell fate decisions, differentiation, proliferation, and apoptosis, particularly in embryonic development and T-cell differentiation. - It is **not the main mechanism** by which glucocorticoids exert their immunosuppressive effects. *Wnt pathway* - The **Wnt pathway** plays a significant role in embryogenesis, tissue homeostasis, and regeneration, particularly in cell proliferation, differentiation, and migration. - It is **not the primary target** for the immunosuppressive action of glucocorticoids in conditions like SLE. *Hippo pathway* - The **Hippo pathway** is essential for organ size control, cell proliferation, and apoptosis, often acting as a tumor suppressor pathway. - While important in cell regulation, it is **not directly inhibited by glucocorticoids** to achieve immune suppression.

Question 174: A 44-year-old woman is being treated by her oncologist for metastatic breast cancer. The patient had noticed severe weight loss and a fixed breast mass over the past 8 months but refused to see a physician until her husband brought her in. Surgery is scheduled, and the patient is given an initial dose of radiation therapy to destroy malignant cells. Which of the following therapies was administered to this patient?

A. Induction therapy
B. Salvage therapy
C. Adjuvant therapy
D. Consolidation therapy
E. Maintenance therapy
F. Neoadjuvant therapy (Correct Answer)

Explanation: ***Neoadjuvant therapy*** - This therapy refers to treatment given **before the primary definitive treatment** (usually surgery) to shrink the tumor and improve surgical outcomes. - In solid tumors like breast cancer, **radiation or chemotherapy administered before surgery** is called neoadjuvant therapy. - In this case, radiation therapy is given to reduce the size of the fixed breast mass before surgical resection, which is the classic indication for neoadjuvant treatment. *Induction therapy* - This term is primarily used in **hematologic malignancies** (leukemias, lymphomas) to describe initial intensive treatment aimed at achieving remission. - While conceptually similar to neoadjuvant therapy, "induction" is not the standard terminology for pre-operative treatment in solid tumors. *Salvage therapy* - This therapy is used when initial treatments have **failed** or when the disease **recurs** after prior therapy. - Here, the radiation is given as the *initial* treatment before surgery, not as a response to treatment failure. *Adjuvant therapy* - This therapy is given **after the primary treatment** (e.g., surgery) to eliminate remaining microscopic disease and prevent recurrence. - The radiation here is administered *before* surgery, not as a follow-up measure. *Maintenance therapy* - This therapy is administered for an **extended period** at lower doses to prevent cancer growth or recurrence after initial intensive treatment has achieved remission. - This is not applicable to the initial pre-surgical treatment described. *Consolidation therapy* - This therapy is given after induction therapy in hematologic malignancies to **deepen the initial response** or to eliminate residual disease. - This term is not used for pre-operative treatment in solid tumors.

Question 175: An 84-year-old man comes to the emergency department because of lower back pain and lower extremity weakness for 3 weeks. Over the past week, he has also found it increasingly difficult to urinate. He has a history of prostate cancer, for which he underwent radical prostatectomy 8 years ago. His prostate-specific antigen (PSA) level was undetectable until a routine follow-up visit last year, when it began to increase from 0.8 ng/mL to its present value of 64.3 ng/mL (N < 4). An MRI of the spine shows infiltrative vertebral lesions with a collapse of the L5 vertebral body, resulting in cord compression at L4–L5. The patient receives one dose of intravenous dexamethasone and subsequently undergoes external beam radiation. Which of the following cellular changes is most likely to occur as a result of this treatment?

A. Intercalation of neighbouring DNA base pairs
B. Disruption of microtubule assembly
C. Formation of DNA crosslinks
D. Generation of hydroxyl radicals (Correct Answer)
E. Formation of pyrimidine dimers

Explanation: ***Generation of hydroxyl radicals*** - **External beam radiation** primarily causes cellular damage through the **ionization of water molecules**, leading to the formation of highly reactive **hydroxyl radicals**. - These radicals directly damage **DNA**, proteins, and cell membranes, leading to **cell death or apoptosis**, especially in rapidly dividing cells like cancer cells. *Intercalation of neighbouring DNA base pairs* - This mechanism is characteristic of certain **chemotherapeutic agents** (e.g., **doxorubicin**, **daunorubicin**) that insert themselves between stacked DNA base pairs. - This process distorts the DNA helix, interfering with replication and transcription, but it is **not the primary mechanism of radiation therapy**. *Disruption of microtubule assembly* - **Microtubule inhibitors** (e.g., **vincristine**, **paclitaxel**) disrupt the formation or disassembly of microtubules, which are essential for cell division and intracellular transport. - While this is a common mechanism of action for some **chemotherapeutic drugs**, it is **not how radiation therapy works**. *Formation of DNA crosslinks* - **Alkylating agents** (e.g., **cyclophosphamide**, **cisplatin**) form covalent bonds within or between DNA strands, creating crosslinks that prevent DNA replication and transcription. - Though highly damaging to DNA, this is a distinct mechanism of action typically associated with **chemotherapy**, not direct radiation. *Formation of pyrimidine dimers* - **Ultraviolet (UV) radiation** causes the formation of **pyrimidine dimers** (e.g., thymine dimers) in DNA. - This type of DNA damage is characteristic of UV light exposure and is **not the primary mechanism of action for external beam radiation therapy**, which uses higher-energy ionizing radiation.

Question 176: Antituberculosis treatment is started. Two months later, the patient comes to the physician for a follow-up examination. The patient feels well. She reports that she has had tingling and bilateral numbness of her feet for the past 6 days. Her vital signs are within normal limits. Her lips are dry, scaly, and slightly swollen. Neurologic examination shows decreased sensation to pinprick and light touch over her feet, ankles, and the distal portion of her calves. Laboratory studies show: Leukocyte count 7400 /mm3 RBC count 2.9 million/mm3 Hemoglobin 10.8 g/dL Hematocrit 30.1% Mean corpuscular volume 78 fL Mean corpuscular hemoglobin 24.2 pg/cell Platelet count 320,000/mm3 Serum Glucose 98 mg/dL Alanine aminotransferase (ALT) 44 U/L Aspartate aminotransferase (AST) 52 U/L Administration of which of the following is most likely to have prevented this patient's neurological symptoms?

A. Interferon beta
B. Iron
C. Vitamin B12
D. Vitamin E
E. Pyridoxine (Correct Answer)

Explanation: ***Pyridoxine*** - The patient is experiencing **peripheral neuropathy** (tingling, numbness in feet) and **cheilosis** (dry, scaly, swollen lips), which are characteristic side effects of **isoniazid** (an antituberculosis drug). - Isoniazid interferes with **pyridoxine (vitamin B6)** metabolism, leading to its deficiency, which can be prevented by co-administering **pyridoxine** with isoniazid. *Interferon beta* - **Interferon beta** is primarily used in the treatment of **multiple sclerosis** to reduce the frequency and severity of relapses by modulating the immune system. - It is not related to the metabolic pathways or side effects of antituberculosis medications and would not prevent these neurologic symptoms. *Iron* - The patient's mild microcytic anemia (low Hb, low MCV, low MCH) could suggest **iron deficiency**, but this is not the primary cause of her neurological symptoms. - While iron supplementation would address the anemia, it would not prevent the **isoniazid-induced peripheral neuropathy** or cheilosis. *Vitamin B12* - **Vitamin B12 deficiency** can cause peripheral neuropathy and anemia, often **macrocytic anemia**, but the patient here has **microcytic anemia** and cheilosis. - Furthermore, the symptoms are characteristic of **isoniazid-induced pyridoxine deficiency** occurring during antituberculosis treatment, rather than an underlying B12 deficiency. *Vitamin E* - **Vitamin E deficiency** can cause neurological symptoms, including neuropathy and ataxia, due to its role as an **antioxidant** protecting nerve membranes. - However, there is no direct link between antituberculosis drugs like isoniazid and vitamin E deficiency, and supplementation would not prevent the specific neurological symptoms seen here.

Question 177: A 62-year-old woman presents to the clinic with a lacerated wound on her left forearm. She got the wound accidentally when she slipped in her garden and scraped her hand against some nails sticking out of the fence. The patient has rheumatoid arthritis and takes methylprednisolone 16 mg/day. She cannot recall her vaccination history. On physical examination her blood pressure is 140/95 mm Hg, heart rate is 81/min, respiratory rate is 16/min, and temperature is 36.9°C (98.4°F). The wound is irregularly shaped and lacerated and measures 4 × 5 cm with a depth of 0.5 cm. It is contaminated with dirt. The physician decides to administer both the tetanus toxoid and immunoglobulin after wound treatment. What is true regarding the tetanus prophylaxis in this patient?

A. It does not make sense to administer tetanus toxoid as it will fail to induce sufficient immunity in a patient who takes oral glucocorticoids.
B. The immunoglobulin administration will provide sufficient levels of anti-tetanus toxin antibodies until the production of the patient’s own antibodies starts. (Correct Answer)
C. It does not make sense to administer tetanus toxoid as it will fail to induce sufficient immunity in patients aged more than 60 years.
D. The immunoglobulin is given to this patient to promote the action of the toxoid and antibody production.
E. Immunoglobulin administration can provide constant levels of antibodies in the patient’s blood for more than 4 months.

Explanation: ***The immunoglobulin administration will provide sufficient levels of anti-tetanus toxin antibodies until the production of the patient’s own antibodies starts.*** * **Tetanus immunoglobulin (TIG)** provides immediate, but temporary, passive immunity through pre-formed antibodies, crucial for high-risk wounds in unvaccinated or immunocompromised individuals. * This **passive immunity** offers immediate protection while the patient's immune system begins to mount an active response to the **tetanus toxoid vaccine**. *It does not make sense to administer tetanus toxoid as it will fail to induce sufficient immunity in a patient who takes oral glucocorticoids.* * While **glucocorticoids (like methylprednisolone)** can reduce the immune response, **tetanus toxoid** vaccination is still recommended, although the immune response might be attenuated. * A **reduced, but still present, immune response** from vaccination in combination with passive immunity from TIG offers better long-term protection than TIG alone. *It does not make sense to administer tetanus toxoid as it will fail to induce sufficient immunity in patients aged more than 60 years.* * **Age alone** is not a contraindication for tetanus toxoid vaccination; while the immune response may be somewhat reduced in older adults, it can still provide significant protection. * The **immunogenicity of tetanus toxoid** remains high in older adults, and it is part of routine vaccination schedules for all ages. *The immunoglobulin is given to this patient to promote the action of the toxoid and antibody production.* * **Immunoglobulin (TIG)** provides immediate passive immunity; it does not promote or enhance the active immune response induced by the **tetanus toxoid vaccine**. * The toxoid stimulates the patient's own immune system to produce antibodies, a process that is separate from the immediate, temporary protection offered by immunoglobulin. *Immunoglobulin administration can provide constant levels of antibodies in the patient’s blood for more than 4 months.* * **Tetanus immunoglobulin** provides only **short-term passive immunity**, with antibodies typically lasting for a few weeks to a few months, not more than 4 months. * For long-term protection, **active immunization with tetanus toxoid** is necessary, as it induces memory B and T cells.

Question 178: A cell biologist is studying the activity of a novel chemotherapeutic agent against a cancer cell line. After incubation with the agent and cell detachment from the tissue culture plate, the DNA is harvested from the cells and run on a gel. Of note, there are large bands at every multiple of 180 base pairs on the gel. Which of the following explains the pathophysiology of this finding?

A. Protein denaturation
B. Release of lysosomal enzymes
C. Cellular swelling
D. ATP depletion
E. Caspase activation (Correct Answer)

Explanation: ***Caspase activation*** - The presence of large bands at multiples of **180 base pairs** on a gel indicates a characteristic ladder-like fragmentation pattern of DNA. This fragmentation is a hallmark of **apoptosis**, a form of programmed cell death. - **Caspase activation**, particularly that of **endonucleases** like caspase-activated DNase (CAD), is responsible for cleaving DNA between nucleosomes, leading to these distinct 180-bp fragments. *Protein denaturation* - **Protein denaturation** involves the unfolding of proteins due to stressors but does not directly cause DNA fragmentation into specific band sizes. - While it can be a part of apoptosis or necrosis, it's not the primary mechanism explaining the observed **DNA laddering**. *Release of lysosomal enzymes* - **Lysosomal enzymes** are typically released during **necrosis** or severe cellular injury, leading to widespread, indiscriminate degradation of cellular components, including DNA. - This degradation would result in a **smear** rather than discrete bands on a gel, as the DNA would be randomly fragmented. *Cellular swelling* - **Cellular swelling** is an early, reversible sign of cell injury often associated with **necrosis** or hydropic change due to ion pump dysfunction. - It does not directly lead to **DNA fragmentation** or the specific laddering pattern seen in apoptosis. *ATP depletion* - **ATP depletion** is a critical event in cell injury, often leading to activation of anaerobic glycolysis, failure of ion pumps, and ultimately cell death. - While **ATP depletion** can contribute to necrosis, apoptosis often requires ATP for the energy-dependent cascade of caspase activation and DNA fragmentation.

Question 179: A 39-year-old man comes to the physician for a follow-up examination. He was diagnosed with latent tuberculosis infection 3 months ago. He has had generalized fatigue and dyspnea on exertion for the past 6 weeks. He does not smoke and drinks 2–3 beers on weekends. Vital signs are within normal limits. Examination shows conjunctival pallor. Laboratory studies show: Hemoglobin 7.8 g/dL Mean corpuscular volume 72 μm3 Red cell distribution width 17% (N = 13–15) Reticulocyte count 0.7% Leukocyte count 6,800/mm3 Platelet count 175,000/mm3 Serum Creatinine 0.8 mg/dL Iron 246 μg/dL Ferritin 446 ng/mL Total iron-binding capacity 212 μg/dL (N = 250–450) Which of the following is the most likely cause of this patient's symptoms?

A. Iron deficiency
B. Vitamin B12 deficiency
C. Beta thalassemia minor
D. Chronic inflammation
E. Adverse effect of medication (Correct Answer)

Explanation: ***Adverse effect of medication*** - The patient was recently diagnosed with **latent tuberculosis** and would likely have been started on **isoniazid** for treatment. Isoniazid is a well-known cause of **sideroblastic anemia** through interference with **pyridoxine (vitamin B6)** metabolism. - Vitamin B6 is an essential cofactor for **δ-aminolevulinic acid (ALA) synthase**, the rate-limiting enzyme in heme synthesis. Isoniazid-induced B6 deficiency leads to **defective heme synthesis**, resulting in **iron accumulation** in mitochondria of developing erythrocytes (sideroblasts). - This produces the classic pattern of **microcytic anemia** with **markedly elevated serum iron** (246 μg/dL), **high ferritin** (446 ng/mL), and **low TIBC** (212 μg/dL) due to iron overload. The **low reticulocyte count** (0.7%) indicates inadequate bone marrow response. *Iron deficiency* - While this also causes **microcytic anemia** (MCV 72 fL) and **elevated RDW**, the iron studies would show the **opposite pattern**: **low serum iron**, **low ferritin**, and **high TIBC** (>400 μg/dL). - The patient's **very high iron** (246 μg/dL) and **ferritin** (446 ng/mL) definitively rule out iron deficiency. *Vitamin B12 deficiency* - **Vitamin B12 deficiency** causes **macrocytic anemia** (MCV >100 fL), not the **microcytic anemia** seen here (MCV 72 fL). - B12 deficiency would also typically show **hypersegmented neutrophils** and **elevated MCV**, neither of which fit this presentation. *Beta thalassemia minor* - **Beta thalassemia minor** does present with **microcytic anemia** and usually has a **normal or low-normal RDW** (in contrast to the elevated RDW here). - However, thalassemia trait typically shows **normal or slightly low ferritin** and **normal iron studies**, not the marked **iron overload** pattern seen in this patient. - Additionally, thalassemia is a **lifelong genetic condition**, not an acute presentation developing over 6 weeks. *Chronic inflammation* - **Anemia of chronic disease** typically presents with **normocytic** or **mildly microcytic anemia**, **low serum iron**, **high ferritin**, and **low TIBC** due to hepcidin-mediated iron sequestration. - The key distinguishing feature is that this patient has **very high serum iron** (246 μg/dL), which is **not consistent** with anemia of chronic disease, where iron is sequestered in macrophages and serum iron remains low.

Question 180: A 65-year-old G4P4 woman presents to her primary care physician complaining of a breast lump. She reports that she felt the lump while conducting a breast self-examination. Her past medical history is notable for endometrial cancer status post radical hysterectomy. She takes aspirin and fish oil. The patient drinks 3-4 alcoholic beverages per day and has a distant smoking history. Her temperature is 98.6°F (37°C), blood pressure is 130/75 mmHg, pulse is 90/min, and respirations are 18/min. A firm palpable mass in the upper outer quadrant of the right breast is noted on physical exam. Further workup reveals invasive ductal adenocarcinoma. She eventually undergoes radical resection and is started on a medication that is known to inhibit thymidylate synthetase. This patient is at increased risk for which of the following medication adverse effects?

A. Mucositis/stomatitis (Correct Answer)
B. Severe diarrhea
C. Myelosuppression
D. DPD deficiency-related severe toxicity
E. Hand-foot syndrome (palmar-plantar erythrodysesthesia)

Explanation: ***Mucositis/stomatitis*** - The patient is likely undergoing treatment with **5-fluorouracil (5-FU)**, a thymidylate synthase inhibitor used for breast cancer. - **Mucositis** and stomatitis are very common and often dose-limiting side effects of 5-FU, affecting rapidly dividing cells in the oral and gastrointestinal mucosa. *Severe diarrhea* - While diarrhea can occur with 5-FU, **severe diarrhea** is more characteristic of **irinotecan** or other topoisomerase I inhibitors. - The patient's presentation with a breast mass and subsequent treatment with a **thymidylate synthase inhibitor** points away from irinotecan as the primary agent. *Myelosuppression* - **Myelosuppression** (bone marrow suppression) is a common side effect of many chemotherapeutic agents, including 5-FU. - However, **mucositis/stomatitis** is a more prominent and often dose-limiting toxicity for 5-FU compared to myelosuppression, especially when considering the specificity of the question. *DPD deficiency-related severe toxicity* - **Dihydropyrimidine dehydrogenase (DPD) deficiency** can lead to severe and potentially fatal toxicity with **5-FU**, but this is related to a genetic predisposition, not a general adverse effect *risk* for all patients receiving the drug. - The question asks about an increased risk for a general adverse effect, not a specific genetic susceptibility. *Hand-foot syndrome (palmar-plantar erythrodysesthesia)* - **Hand-foot syndrome** is a side effect of some chemotherapies, particularly **capecitabine** (an oral prodrug of 5-FU) and **liposomal doxorubicin**. - While capecitabine is related, the question asks about a medication that inhibits thymidylate synthetase (which 5-FU directly does), and mucositis is a more universal and significant side effect of 5-FU itself.

Question 181: A 26-year-old male currently undergoing standard therapy for a recently diagnosed active tuberculosis infection develops sudden onset of fever and oliguria. Laboratory evaluations demonstrate high levels of eosinophils in both the blood and urine. Which of the following is most likely responsible for the patient's symptoms?

A. Isoniazid
B. Pyrazinamide
C. Rifampin (Correct Answer)
D. Return of active tuberculosis symptoms secondary to patient non-compliance with anti-TB regimen
E. Ethambutol

Explanation: ***Rifampin*** - **Rifampin-induced interstitial nephritis** can present with **fever**, **oliguria**, and **eosinophilia** (in both blood and urine), typically within weeks to months of starting treatment. - This drug commonly causes hypersensitivity reactions affecting the kidneys, leading to **acute kidney injury**. *Isoniazid* - While isoniazid can cause **hepatotoxicity**, **peripheral neuropathy**, and **drug-induced lupus erythematosus**, it is not typically associated with **eosinophilic interstitial nephritis** or **oliguria**. - Its adverse effects do not usually include the specific constellation of symptoms seen in this patient. *Pyrazinamide* - Pyrazinamide is known to cause **hepatotoxicity** (similar to isoniazid) and **hyperuricemia**, which can lead to **gouty arthritis**. - It does not commonly cause **eosinophilic interstitial nephritis** or conditions presenting with **fever**, **oliguria**, and **eosinophilia**. *Return of active tuberculosis symptoms secondary to patient non-compliance with anti-TB regimen* - A return of active tuberculosis would typically manifest as worsening respiratory symptoms, constitutional symptoms (weight loss, night sweats), and possibly new infiltrates on chest X-ray, not primarily acute **fever**, **oliguria**, and **eosinophilia**. - The presented symptoms are more indicative of a **drug-induced hypersensitivity reaction** rather than a relapse of infection. *Ethambutol* - The most significant and well-known adverse effect of ethambutol is **optic neuritis**, leading to **vision impairment** and **color blindness**. - It is not typically associated with **fever**, **oliguria**, or **eosinophilia** indicative of interstitial nephritis.

Question 182: A 65-year-old obese woman presents with changes in her left breast. The patient states that, about a month ago, she noticed that she was able to feel a hard mass in the upper outer quadrant of her left breast, which has not gone away. In addition, her nipple and skin overlying the breast have started to look different. Past medical history is significant for polycystic ovarian syndrome (PCOS) and hypertension, well-managed with lisinopril. The patient has never been pregnant. Menopause was at age 53. Family history is significant for breast cancer in her mother at age 55, and her father who died of lung cancer at age 52. A review of systems is significant for a 13.6 kg (30 lb) weight loss in the last 2 months despite no change in diet or activity. Vitals include: temperature 37.0°C (98.6°F), blood pressure 120/75 mm Hg, pulse 97/min, respiratory rate 16/min, and oxygen saturation 99% on room air. Physical examination is significant for a palpable, hard, fixed mass in the upper outer quadrant of the left breast, as well as nipple retraction and axillary lymphadenopathy. Mammography of the left breast reveals a spiculated mass in the upper outer quadrant. A biopsy confirms invasive ductal carcinoma. Molecular analysis reveals that the tumor cells are positive for HER2/neu receptor, which is associated with a poor prognosis. Which of the following is indicated as first-line targeted therapy for this patient's treatment?

A. Raloxifene
B. Tamoxifen
C. Goserelin
D. Anastrozole
E. Trastuzumab (Correct Answer)

Explanation: ***Trastuzumab*** - The patient's tumor is **positive for HER2/neu receptor**, which is a direct indication for **trastuzumab (Herceptin)**. This monoclonal antibody specifically targets the HER2 receptor, inhibiting the growth of HER2-driven cancer cells. - Trastuzumab is considered **first-line targeted therapy** for HER2-positive breast cancer, often used in combination with chemotherapy, and is known to improve survival outcomes in these patients. *Raloxifene* - **Raloxifene** is a **selective estrogen receptor modulator (SERM)** primarily used to treat and prevent **osteoporosis** in postmenopausal women, and for the prevention of **estrogen receptor (ER)-positive breast cancer**. - It would not be indicated as a first-line targeted therapy for this patient because her cancer is **HER2-positive**, not explicitly ER-positive (though ER status is not provided, HER2 positivity is the guiding factor for specific targeted therapy). *Tamoxifen* - **Tamoxifen** is also a **selective estrogen receptor modulator (SERM)**, used in the treatment of **estrogen receptor (ER)-positive breast cancer** in both pre- and postmenopausal women. - It works by blocking estrogen's effects on breast cancer cells, which is not the primary mechanism of action required for a **HER2-positive tumor**. *Goserelin* - **Goserelin** is a **gonadotropin-releasing hormone (GnRH) agonist** that suppresses ovarian function, reducing estrogen production. It is used in premenopausal women with **hormone receptor-positive breast cancer**. - This patient is postmenopausal, and her cancer is **HER2-positive**, not necessarily hormone receptor-positive, making goserelin an inappropriate choice for targeted therapy. *Anastrozole* - **Anastrozole** is an **aromatase inhibitor** used in postmenopausal women with **hormone receptor-positive breast cancer** to block the production of estrogen in peripheral tissues. - While the patient is postmenopausal, her cancer's defining characteristic for targeted therapy is its **HER2-positivity**, not explicitly its hormone receptor status. Aromatase inhibitors are not targeted therapy for HER2-positive disease.

Question 183: A 23-year-old man comes to the physician because of a 1-week history of muscle ache, fatigue, and fever that occurs every 2 days. He recently returned from a trip to Myanmar. A peripheral blood smear shows erythrocytes with brick-red granules. The physician recommends a combination of two antimicrobial drugs after confirming normal glucose-6-phosphate dehydrogenase activity. Which of the following is the most appropriate rationale for dual therapy?

A. Decrease in renal drug secretion
B. Therapy against polymicrobial infections
C. Prevention of infection relapse (Correct Answer)
D. Prevention of drug resistance
E. Decrease in enzymatic drug deactivation

Explanation: ***Prevention of infection relapse*** - The patient's symptoms (fever every 2 days, muscle ache, fatigue after travel to Myanmar) and blood smear findings (**erythrocytes with brick-red granules**, or **Schüffner's dots**, indicating **Plasmodium vivax** or **P. ovale** infection) strongly suggest **malaria**. - Dual therapy in this context typically involves a **blood-stage antimalaria** (e.g., chloroquine, artemisinin combination therapy) to treat acute symptoms and a **hypnozoiticidal drug** (e.g., **primaquine**) to clear dormant liver stages (**hypnozoites**) of P. vivax/ovale and prevent relapse. *Decrease in renal drug secretion* - This is not a primary reason for dual therapy in malaria; drug secretion rates are generally considered when determining individual drug dosages, not for combining multiple drugs. - While drug interactions can affect renal clearance, it's not the rationale for dual antimalarial use in this common clinical scenario. *Therapy against polymicrobial infections* - The presentation is classic for **monomicrobial malaria** due to Plasmodium vivax or ovale, not a polymicrobial bacterial or fungal infection. - Antimicrobial combinations for polymicrobial infections target different classes of microbes, which is not the case here. *Prevention of drug resistance* - While combination therapy is crucial for **preventing drug resistance** in infections like TB or HIV, and also for blood-stage malarial treatment (e.g., artemisinin combination therapy), the specific dual therapy mentioned (blood-stage drug + primaquine) is primarily for **eradicating hypnozoites** to prevent relapse, not solely for preventing blood-stage drug resistance. - However, in cases of **falciparum malaria**, combination therapy is indeed used to prevent resistance. The brick-red granules, though, point to non-falciparum malaria. *Decrease in enzymatic drug deactivation* - This concept relates to pharmacokinetic interactions where one drug might inhibit enzymes that metabolize another, increasing its effectiveness or toxicity. - This is not the primary purpose of combining a blood-stage antimalarial with primaquine; the primary goal is to target multiple life stages of the parasite.

Question 184: A 25-year-old medical student is doing an international health elective in the Amazon River basin studying tropical disease epidemiology. As part of his pre-trip preparation, he wants to be protected from malaria and is researching options for prophylaxis. Which of the following agents should be avoided for malarial prophylaxis in this patient?

A. Doxycycline
B. Mefloquine
C. Atovaquone-proguanil
D. Quinine
E. Chloroquine (Correct Answer)

Explanation: ***Chloroquine*** - Chloroquine is generally ineffective for malaria prophylaxis in regions with **chloroquine-resistant strains**, which includes most of the **Amazon River basin**. - Widespread resistance, particularly from *Plasmodium falciparum*, makes it a poor choice for travelers to many endemic areas. *Doxycycline* - **Doxycycline** is a highly effective and commonly used agent for malaria prophylaxis in areas with **drug-resistant malaria**. - It is taken daily and should be started 1-2 days before travel and continued for 4 weeks after leaving the endemic area. *Mefloquine* - **Mefloquine** is a good option for prophylaxis in areas with **multidrug-resistant *P. falciparum***, effective even in regions with high chloroquine resistance. - However, it has significant central nervous system **side effects**, including psychiatric and neurological issues, which may limit its use in some individuals. *Atovaquone-proguanil* - **Atovaquone-proguanil** (Malarone) is an effective and well-tolerated prophylactic agent for malaria, including in areas with **chloroquine-resistant strains**. - It has a convenient dosing schedule (started 1-2 days before travel and continued for only 7 days after leaving) and relatively few side effects. *Quinine* - **Quinine** is an effective **treatment** for malaria but is generally not recommended for prophylaxis due to its **short half-life** and significant **side effects** even at prophylactic doses (e.g., cinchonism). - Its use is typically reserved for the treatment of acute, severe malaria episodes.

Question 185: A 65-year-old man presents with a small painless ulcer with a raised border on his right forearm which has persisted for the last 3 weeks. His past history is significant for 3 occurrences of basal cell carcinoma on different areas of the body during the last 4 years, which have all been surgically excised. The morphology of the present lesion is also highly suggestive of basal cell carcinoma. The patient says that, if the lesion is a basal cell carcinoma, he does not want to undergo biopsy and surgery if it can be avoided. The patient is prescribed a cream, which is FDA-approved for the treatment of small superficial basal cell carcinomas in low-risk areas. The cream contains a chemotherapeutic agent, which is an antimetabolite and an S-phase-specific anticancer drug. Which of the following best explains the mechanism of action of this cream?

A. Inhibition of DNA repair
B. Inhibition of de novo purine nucleotide synthesis
C. Inhibition of dihydrofolate reductase
D. Inhibition of ribonucleotide reductase
E. Inhibition of thymidylate synthase (Correct Answer)

Explanation: ***Inhibition of thymidylate synthase*** - The cream contains **5-fluorouracil (5-FU)**, which is an **antimetabolite** and an **S-phase-specific** chemotherapeutic agent. - 5-FU is converted to 5-fluorodeoxyuridine monophosphate (5-FdUMP), which **irreversibly inhibits thymidylate synthase**, thereby blocking the synthesis of deoxythymidine triphosphate (dTTP) and ultimately **DNA synthesis**. *Inhibition of DNA repair* - While some chemotherapeutic agents affect DNA repair, this is not the primary mechanism of action for **antimetabolites targeting S-phase DNA synthesis**. - Drugs like alkylating agents or platinum compounds primarily damage DNA, and their effects might indirectly involve DNA repair pathways. *Inhibition of de novo purine nucleotide synthesis* - This is the mechanism of action for drugs like **6-mercaptopurine** or **azathioprine**, which are purine analogs. - The patient is described as receiving an antimetabolite that affects DNA synthesis in the S-phase, which points more directly to pyrimidine synthesis inhibition for 5-FU. *Inhibition of dihydrofolate reductase* - This is the mechanism of action for **methotrexate**, which is an antimetabolite that inhibits the conversion of dihydrofolate to tetrahydrofolate. - This inhibition prevents the synthesis of purines and thymidylate, but it is not the direct mechanism of action for the drug used in this context (5-FU). *Inhibition of ribonucleotide reductase* - This is the mechanism of action for drugs like **hydroxyurea** or **gemcitabine**. - Ribonucleotide reductase converts ribonucleotides to deoxyribonucleotides, which are essential for DNA synthesis, but this is a separate target from thymidylate synthase.

Question 186: A 55-year-old man presents to his primary care physician for a regular check-up. The patient was born in Germany in 1960 with shortened limbs, underdeveloped digits, absent external ears, and a cleft palate. He is currently in a wheelchair. His past medical history is also notable for hypertension and allergies. He takes lisinopril daily and loratadine as needed. His mother had a complicated past medical history and took multiple medications during her pregnancy. His temperature is 98.6°F (37°C), blood pressure is 120/80 mmHg, pulse is 90/min, and respirations are 20/min. The drug that most likely caused this patient's condition is also indicated for which of the following?

A. Acne vulgaris
B. Multiple myeloma (Correct Answer)
C. Deep venous thrombosis
D. Recurrent miscarriage
E. Bipolar disease

Explanation: ***Multiple myeloma*** - The patient's presentation with **shortened limbs**, **underdeveloped digits**, **absent external ears**, and a **cleft palate**, born in Germany in 1960, is highly characteristic of **thalidomide embryopathy**. - **Thalidomide**, the drug responsible for these birth defects, is currently used in adults for treating **multiple myeloma** due to its anti-angiogenic and immunomodulatory properties. *Acne vulgaris* - **Thalidomide** is not indicated for the treatment of **acne vulgaris**. - **Acne vulgaris** is typically treated with retinoids (topical or oral), antibiotics, or hormonal therapies. *Deep venous thrombosis* - While certain medications can cause or prevent **deep venous thrombosis (DVT)**, **thalidomide** itself is not primarily indicated for DVT treatment or prevention. - In fact, Thalidomide has been associated with an **increased risk of thrombosis**, especially when combined with steroids, which often necessitates DVT prophylaxis when used for multiple myeloma. *Recurrent miscarriage* - **Thalidomide** is a severe **teratogen** and would absolutely not be used to treat or prevent recurrent miscarriage. - Its use during pregnancy can lead to severe developmental anomalies, as seen in the patient's history. *Bipolar disease* - **Thalidomide** has no established role in the treatment of **bipolar disease**. - Mood stabilizers such as lithium, valproate, lamotrigine, and atypical antipsychotics are common treatments for bipolar disorder.

Question 187: A 30-year-old man who was recently placed on TMP-SMX for a urinary tract infection presents to urgent care with a new rash. The vital signs include: blood pressure 121/80 mm Hg, pulse 91/min, respiratory rate 18/min, and temperature 36.7°C (98.2°F). Physical examination reveals a desquamative skin covering both of his lower extremities. A basic chemistry panel reveal sodium 139 mmol/L, potassium 3.8 mmol/L, chloride 110 mmol/L, carbon dioxide 47, blood urea nitrogen 23 mg/dL, creatinine 0.9 mg/dL, and glucose 103 mg/dL. Which of the following is the most likely diagnosis?

A. Atopic dermatitis
B. Steven-Johnson syndrome (SJS) (Correct Answer)
C. Dermatitis herpetiformis
D. Seborrheic dermatitis
E. Toxic epidermal necrolysis (TEN)

Explanation: ***Steven-Johnson syndrome (SJS)*** - The presentation of a **desquamative rash** following recent administration of **TMP-SMX (trimethoprim-sulfamethoxazole)**, a known culprit drug, is highly suggestive of SJS. - SJS is a severe form of **cutaneous adverse drug reaction** involving mucocutaneous lesions and epidermal detachment, typically less than 10% of the body surface area. *Atopic dermatitis* - Characterized by **eczematous, pruritic lesions** that are often chronic and recurrent. - It is not typically associated with acute, widespread **desquamation** following drug exposure. *Dermatitis herpetiformis* - Presents with **pruritic, vesicular lesions** primarily on extensor surfaces. - It is strongly associated with **celiac disease** and is not typically drug-induced. *Seborrheic dermatitis* - Manifests as **erythematous patches** with greasy scales, commonly affecting areas rich in sebaceous glands مثل the scalp, face, and chest. - It does not involve acute **desquamation** or a clear association with TMP-SMX. *Toxic epidermal necrolysis (TEN)* - While TEN is also a severe cutaneous adverse drug reaction, it involves **extensive epidermal detachment** covering more than 30% of the body surface area. - This patient's rash, described as covering both lower extremities, is more consistent with SJS due to the lesser extent of involvement.

Question 188: A 33-year-old man is being evaluated for malaise and fatigability. He says that he hasn’t been able to perform at work, can’t exercise like before, and is constantly tired. He also says that his clothes have ‘become larger’ in the past few months. Past medical history is significant for gastroesophageal reflux disease, which is under control with lifestyle changes. His blood pressure is 110/70 mm Hg, the temperature is 37.0°C (98.6°F), the respiratory rate is 17/min, and the pulse is 82/min. On physical examination, an enlarged, painless, mobile, cervical lymph node is palpable. A complete blood count is performed. Hemoglobin 9.0 g/dL Hematocrit 37.7% Leukocyte count 5,500/mm3 Neutrophils 65% Lymphocytes 30% Monocytes 5% Mean corpuscular volume 82.2 μm3 Platelet count 190,000 mm3 Erythrocyte sedimentation rate 35 mm/h C-reactive protein 8 mg/dL A biopsy of the lymph node is performed which reveals both multinucleated and bilobed cells. The patient is started on a regimen of drugs for his condition. Echocardiography is performed before treatment is started and shows normal ejection fraction, ventricle function, and wall motion. After 2 rounds of chemotherapy, another echocardiography is performed by protocol, but this time all heart chambers are enlarged, and the patient is suffering from severe exertion dyspnea. Which of the drugs below is most likely responsible for these side effects?

A. Dacarbazine
B. Vinblastine
C. Rituximab
D. Bleomycin
E. Adriamycin (Correct Answer)

Explanation: ***Adriamycin*** - **Adriamycin** (doxorubicin) is a known cardiotoxic agent, especially with cumulative doses, leading to **dilated cardiomyopathy** and heart failure, as described by the enlarged heart chambers and severe dyspnea. - The delayed onset of cardiac symptoms after two rounds of chemotherapy is consistent with Adriamycin's mechanism of causing **oxidative stress** and damage to myocardial cells. *Dacarbazine* - **Dacarbazine** is an alkylating agent, primarily associated with side effects such as **myelosuppression**, nausea, vomiting, and flu-like symptoms. - It does not typically cause the severe **cardiotoxicity** observed in this patient. *Vinblastine* - **Vinblastine** is a vinca alkaloid that primarily causes **neurotoxicity** (e.g., peripheral neuropathy, constipation), myelosuppression, and jaw pain. - Significant **cardiac side effects** like dilated cardiomyopathy are not characteristic of vinblastine. *Rituximab* - **Rituximab** is a monoclonal antibody targeting CD20 and is generally well-tolerated, though it can cause **infusion-related reactions** and an increased risk of infections. - It is not associated with direct **cardiotoxicity** leading to dilated cardiomyopathy. *Bleomycin* - **Bleomycin** is an antitumor antibiotic primarily known for its association with **pulmonary fibrosis** (bleomycin lung), hyperpigmentation, and skin toxicities. - While it can cause some cardiac abnormalities, **dilated cardiomyopathy** is not its hallmark cardiac side effect; it's far less cardiotoxic than Adriamycin.

Question 189: A 41-year-old man presents to the emergency department with several days of hand tremor, vomiting, and persistent diarrhea. His wife, who accompanies him, notes that he seems very “out of it.” He was in his usual state of health last week and is now having difficulties at work. He has tried several over-the-counter medications without success. His past medical history is significant for bipolar disorder and both type 1 and type 2 diabetes. He takes lithium, metformin, and a multivitamin every day. At the hospital, his heart rate is 90/min, respiratory rate is 17/min, blood pressure is 130/85 mm Hg, and temperature is 37.0°C (98.6°F). The man appears uncomfortable. His cardiac and respiratory exams are normal and his bowel sounds are hyperactive. His lithium level is 1.8 mEq/L (therapeutic range, 0.6–1.2 mEq/L). Which of the following may have contributed to this patient’s elevated lithium level?

A. Large amounts of caffeine intake
B. Decreased salt intake (Correct Answer)
C. Weight loss
D. Addition of lurasidone to lithium therapy
E. Addition of fluoxetine to lithium therapy

Explanation: **Decreased salt intake** - **Lithium** is reabsorbed in the renal tubules alongside **sodium**. When **sodium intake** is low, the kidneys reabsorb more sodium and, inadvertently, more lithium, leading to increased serum lithium levels and potential toxicity. - The patient's **vomiting and diarrhea** can cause significant fluid and electrolyte loss, including sodium. This **depletion of sodium** would then lead to increased lithium reabsorption and toxicity. *Large amounts of caffeine intake* - **Caffeine** is a diuretic, which can increase **lithium excretion** and potentially *lower* lithium levels. - Therefore, large amounts of caffeine intake are unlikely to contribute to an *elevated* lithium level. *Weight loss* - **Weight loss** itself does not directly influence **lithium metabolism** or excretion in a way that would cause an elevated lithium level. - While dehydration associated with weight loss could theoretically impact lithium, mere weight loss is not a primary contributor to toxicity. *Addition of lurasidone to lithium therapy* - There is no significant pharmacological interaction between **lurasidone** and **lithium** that would directly lead to elevated lithium levels. Both medications are used in bipolar disorder, and lurasidone is not known to inhibit lithium excretion or metabolism. - Adding lurasidone to lithium therapy is generally considered safe with respect to lithium levels. *Addition of fluoxetine to lithium therapy* - **Fluoxetine** (an SSRI) typically has *minimal or inconsistent effects* on **lithium levels**. Some reports suggest a possible *slight increase* in lithium levels in some individuals, but it is not a common or strong interaction that would explain a toxic level to the extent seen here. - The more significant interactions leading to lithium toxicity are generally related to **sodium and fluid balance**, which are strongly affected by the patient's current symptoms.

Question 190: A 47-year-old female with a history of poorly controlled type I diabetes mellitus and end-stage renal disease undergoes an allogeneic renal transplant. Her immediate post-operative period is unremarkable and she is discharged from the hospital on post-operative day 4. Her past medical history is also notable for major depressive disorder, obesity, and gout. She takes sertraline, allopurinol, and insulin. She does not smoke or drink alcohol. To decrease the risk of transplant rejection, her nephrologist adds a medication known to serve as a precursor to 6-mercaptopurine. Following initiation of this medication, which of the following toxicities should this patient be monitored for?

A. Pancytopenia (Correct Answer)
B. Cytokine storm
C. Hyperlipidemia
D. Osteoporosis
E. Hirsutism

Explanation: ***Pancytopenia*** - The medication described, a precursor to **6-mercaptopurine (6-MP)**, is **azathioprine**. Azathioprine is an **antimetabolite** that suppresses the immune system by interfering with purine synthesis. - Its main toxicity is **bone marrow suppression**, leading to **pancytopenia** (decreased red blood cells, white blood cells, and platelets), which necessitates close monitoring of **complete blood count (CBC)**. *Cytokine storm* - A **cytokine storm** is a severe systemic inflammatory response, often seen with certain immunotherapies (e.g., **CAR T-cell therapy**) or severe infections. - It is not a typical side effect of **azathioprine** used for transplant rejection prophylaxis. *Hyperlipidemia* - **Hyperlipidemia** is a common side effect of some immunosuppressants like **corticosteroids** and **calcineurin inhibitors (e.g., cyclosporine, tacrolimus)**, which are also used in transplant patients. - However, it is not a direct or primary toxicity associated with **azathioprine**. *Osteoporosis* - **Osteoporosis** is a significant long-term complication associated with **corticosteroid use** in transplant patients. - While many transplant patients receive corticosteroids, **azathioprine** itself does not directly cause osteoporosis as a primary toxicity. *Hirsutism* - **Hirsutism** (excessive hair growth) is a characteristic side effect of **cyclosporine**, another immunosuppressant commonly used in transplant recipients. - This symptom is not typically associated with **azathioprine** therapy.

Question 191: A 58-year-old woman comes to the physician for evaluation of worsening fatigue for 1 week. She also has a 1-year history of hand pain and stiffness. Four months ago, she started a new medication for these symptoms. Medications used prior to that included ibuprofen, prednisone, and hydroxychloroquine. Examination shows a subcutaneous nodule on her left elbow and old joint destruction with Boutonniere deformity. Her hemoglobin concentration is 10.1 g/dL, leukocyte count is 3400/mm3, and platelet count is 101,000/mm3. Methylmalonic acid levels are normal. Which of the following could have prevented this patient's laboratory abnormalities?

A. Vitamin B12
B. Vitamin B6
C. Amifostine
D. 2-Mercaptoethanesulfonate
E. Leucovorin (Correct Answer)

Explanation: **Leucovorin** - The patient's pancytopenia (anemia, leukopenia, and thrombocytopenia) in the context of rheumatoid arthritis treatment points towards **methotrexate toxicity** as the cause. - **Leucovorin (folinic acid)** is often co-administered with methotrexate or used as a rescue therapy to prevent or counteract its adverse effects by providing an alternative source of folate, bypassing the dihydrofolate reductase inhibition. *Vitamin B12* - While **vitamin B12 deficiency** can cause anemia and pancytopenia, the patient's normal **methylmalonic acid levels** rule out this possibility. - B12 deficiency is typically associated with **macrocytic anemia** and neurological symptoms, which are not explicitly mentioned as the primary concern here. *Vitamin B6* - **Vitamin B6 (pyridoxine)** deficiency can lead to microcytic anemia, but it is not typically associated with the comprehensive pancytopenia observed here, nor is it related to methotrexate toxicity. - It is crucial for **heme synthesis** and can be deficient in conditions like alcoholism. *Amifostine* - **Amifostine** is a cytoprotective agent used to prevent nephrotoxicity and ototoxicity associated with certain chemotherapy agents like **cisplatin**, and also to reduce xerostomia in head and neck radiation. - It is not indicated for the prevention of methotrexate-induced myelosuppression. *2-Mercaptoethanesulfonate* - **2-Mercaptoethanesulfonate (Mesna)** is a uroprotectant used to prevent hemorrhagic cystitis caused by **oxazaphosphorine chemotherapeutic agents** like cyclophosphamide and ifosfamide. - It has no role in preventing the hematologic toxicity of methotrexate.

Question 192: A 46-year-old woman comes to the physician because of a 3-day history of diarrhea and abdominal pain. She returned from a trip to Egypt 4 weeks ago. Her vital signs are within normal limits. There is mild tenderness in the right lower quadrant. Stool studies show occult blood and unicellular organisms with engulfed erythrocytes. Which of the following is the most appropriate initial pharmacotherapy for this patient?

A. Paromomycin
B. Doxycycline
C. Metronidazole (Correct Answer)
D. Ciprofloxacin
E. Albendazole

Explanation: **Metronidazole** - **Unicellular organisms with engulfed erythrocytes** in stool are characteristic of **Entamoeba histolytica** infection, causing **amebic dysentery**. - **Metronidazole** is the drug of choice for treating invasive amebiasis, including dysentery and amebic liver abscess. *Paromomycin* - **Paromomycin** is an **intraluminal amebicide** used to eradicate cysts and prevent recurrence, but it is not effective against invasive disease. - It is often used as a follow-up therapy after metronidazole to clear any remaining luminal cysts. *Doxycycline* - **Doxycycline** is a **tetracycline antibiotic** used primarily for bacterial infections, such as those caused by Rickettsia, Chlamydia, and Mycoplasma. - It has no significant activity against **Entamoeba histolytica**. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** used for various bacterial infections, including traveler's diarrhea caused by bacteria like E. coli. - It is not effective against **protozoal infections** like amebiasis. *Albendazole* - **Albendazole** is an **anthelmintic drug** primarily used to treat infections caused by various parasitic worms, such as roundworms, hookworms, and tapeworms. - It is not indicated for the treatment of **amebiasis**.

Question 193: A previously healthy 5-year-old boy is brought to the emergency department because of abdominal pain and vomiting for 6 hours. His mother immediately brought him after noticing that he had gotten into the medicine cabinet. He appears uncomfortable. His temperature is 37.2°C (99°F), pulse is 133/min and blood pressure is 80/50 mm Hg. Examination shows diffuse abdominal tenderness; there is no guarding or rigidity. Digital rectal examination shows dark-colored stools. Laboratory studies show: Hemoglobin 13.2 g/dL Leukocyte count 14,100/mm3 Serum Na+ 136 mEq/L K+ 3.3 mEq/L Cl- 105 mEq/L Urea nitrogen 26 mg/dL Glucose 98 mg/dL Creatinine 1.1 mg/dL Arterial blood gas analysis on room air shows: pH 7.31 pCO2 32 mm Hg HCO3- 16 mEq/L Intravenous fluids are administered. Which of the following is the most appropriate next step in management?

A. Syrup of ipecac
B. Deferoxamine (Correct Answer)
C. Sodium bicarbonate
D. Calcium EDTA
E. Activated charcoal

Explanation: ***Deferoxamine*** - The clinical presentation, including **abdominal pain**, **vomiting**, **hypotension**, and **dark-colored stools** (suggesting gastrointestinal bleeding), in a child who accessed a medicine cabinet, is highly suspicious for **iron poisoning**. - **Deferoxamine** is a **chelating agent** specifically used to treat **acute iron toxicity** by binding to free iron and promoting its excretion. *Syrup of ipecac* - **Syrup of ipecac** is **contraindicated** in cases of suspected poisoning, especially with corrosive substances or in patients with altered mental status, due to the risk of aspiration and lack of proven benefit. - It induces vomiting, which can be harmful given the patient's current symptoms and potential for further esophageal irritation if iron pills are still present. *Sodium bicarbonate* - While the patient has **metabolic acidosis** (pH 7.31, HCO3- 16), **sodium bicarbonate** is used for significant acidosis and hyperkalemia but does not treat the underlying **iron toxicity**. - Addressing the underlying cause with a chelating agent is the priority before symptomatic treatment of acidosis unless it is severe and life-threatening. *Calcium EDTA* - **Calcium EDTA** is a chelating agent primarily used for **lead poisoning**, not iron poisoning. - Using the wrong chelating agent will be ineffective and could potentially cause further harm due to adverse effects. *Activated charcoal* - **Activated charcoal** is **ineffective at binding iron** and is therefore not indicated in cases of iron poisoning. - It is useful for adsorbing many other toxins in the gastrointestinal tract, but not heavy metals like iron.

Question 194: A 33-year-old man presents to the emergency room for diarrhea. He states it is profuse and watery and has not been improving over the past week. He is generally healthy; however, he was recently hospitalized during spring break and treated for alcohol intoxication and an aspiration pneumonia. While on spring break, the patient also went camping and admits eating undercooked chicken and drinking from mountain streams. His temperature is 100.5°F (38.1°C), blood pressure is 111/74 mmHg, pulse is 110/min, respirations are 16/min, and oxygen saturation is 98% on room air. Physical exam is notable for a fatigued appearing man. His abdomen is non-tender. Which of the following is the best management of this patient?

A. Ciprofloxacin
B. Ciprofloxacin and metronidazole
C. No treatment indicated
D. Vancomycin (Correct Answer)
E. Metronidazole

Explanation: ***Vancomycin*** - This patient's recent **hospitalization** and **pneumonia** treatment, followed by persistent watery diarrhea, strongly suggests **Clostridioides difficile infection (CDI)**. - **Oral vancomycin** is a first-line treatment for non-severe C. difficile infection. *Ciprofloxacin* - **Fluoroquinolones** such as ciprofloxacin are often associated with an **increased risk of C. difficile infection**, as they can disrupt the normal gut flora. - They are generally not indicated for watery diarrhea where C. difficile is suspected unless there is strong evidence of a different bacterial pathogen susceptible to ciprofloxacin. *Ciprofloxacin and metronidazole* - While metronidazole is used for C. difficile, **ciprofloxacin is contraindicated** due to its association with CDI development and potential for resistance. - This combination is not appropriate for suspected C. difficile, and the patient's symptoms do not clearly indicate a need for broad-spectrum empirical coverage against other bacterial causes. *No treatment indicated* - The patient presents with **persistent, profuse watery diarrhea** for a week, a low-grade fever, and a history suggestive of C. difficile risk, indicating that medical intervention is needed. - Delaying treatment could lead to worsening symptoms, **dehydration**, and more severe outcomes associated with CDI. *Metronidazole* - **Metronidazole** is an alternative treatment for **mild-to-moderate C. difficile infection**. - However, **oral vancomycin** is generally preferred for its superior efficacy in initial episodes of non-severe CDI.

Question 195: A 45-year-old man presents with worsening joint pain and stiffness. Past medical history is significant for rheumatoid arthritis, diagnosed 3 months ago and managed with celecoxib and methotrexate, and occasional gastric reflux, managed with omeprazole. His vitals are a pulse of 80/min, a respiratory rate of 16/min, and blood pressure of 122/80 mm Hg. On physical examination, the left wrist is swollen, stiff, and warm to touch, and the right wrist is red and warm. There is limited active and passive range of motion at the proximal interphalangeal and metacarpophalangeal joints of both hands. The remainder of the examination is unremarkable. A plain radiograph of the hands shows progressive degeneration of multiple joints. Another drug, etanercept, is added to help control progressive arthritis. Which of the following diagnostic tests should be ordered before starting this new medication in this patient?

A. Malignancy screening
B. Bleeding time
C. Endoscopy
D. Tuberculosis screening (Correct Answer)
E. Antinuclear antibody (ANA) level

Explanation: ***Tuberculosis screening*** - **Etanercept** is a TNF-α inhibitor, which **suppresses the immune system** and increases the risk of **reactivation of latent infections**, particularly **tuberculosis**. - Screening for latent tuberculosis with a **PPD test** or **interferon-gamma release assay (IGRA)** is crucial before initiating therapy with TNF-α inhibitors. *Malignancy screening* - While TNF-α inhibitors have been associated with a **slightly increased risk of certain malignancies**, routine general malignancy screening beyond age-appropriate guidelines is not typically required before starting these medications. - The focus before initiating treatment is on **active infections** or reactivatable latent infections. *Bleeding time* - **Etanercept does not directly affect coagulation pathways** or platelet function in a way that necessitates a routine bleeding time test before administration. - Bleeding time is generally not a standard pre-screening test for TNF-α inhibitors. *Endoscopy* - An endoscopy is not a standard pre-screening test for initiating etanercept therapy. The patient's history of **gastric reflux managed with omeprazole** does not, in itself, mandate an endoscopy before starting this medication. - While GI issues can be present, there's no direct contraindication or increased risk associated with etanercept that would necessitate this procedure beforehand unless other specific symptoms arise. *Antinuclear antibody (ANA) level* - **ANA levels** are often elevated in autoimmune conditions like rheumatoid arthritis, but they are generally** not monitored or tested prior to initiating etanercept**. - While **drug-induced lupus** is a rare side effect of TNF-α inhibitors, an elevated ANA beforehand does not contraindicate its use, nor does it typically trigger pre-treatment ANA testing.

Question 196: Several weeks after starting a new medication for rheumatoid arthritis, a 44-year-old woman comes to the physician because of painful ulcers in her mouth. Oral examination shows inflammation and swelling of the tongue and oropharynx and ulcers on the buccal mucosa bilaterally. Skin examination shows soft tissue swelling over her proximal interphalangeal joints and subcutaneous nodules over her elbows. Serum studies show an alanine aminotransferase level of 220 U/L, aspartate aminotransferase level of 214 U/L, and creatinine level of 1.7 mg/dL. Which of the following is the most likely primary mechanism of action of the drug she is taking?

A. Inhibition of thymidylate synthase
B. Inhibition of cyclooxygenase
C. Inhibition of inosine monophosphate dehydrogenase
D. Inhibition of dihydrofolate reductase (Correct Answer)
E. Inhibition of NF-κB

Explanation: ***Inhibition of dihydrofolate reductase*** - The patient's symptoms (oral ulcers, elevated liver enzymes, elevated creatinine) and history (rheumatoid arthritis, new medication) are highly suggestive of **methotrexate toxicity**. - **Methotrexate** is a cornerstone in RA treatment, and its primary mechanism of action is the **inhibition of dihydrofolate reductase**, an enzyme essential for folate metabolism and DNA synthesis. *Inhibition of thymidylate synthase* - While inhibition of thymidylate synthase is a mechanism of some anticancer drugs like **5-fluorouracil**, it is not the primary mechanism of action of drugs commonly used for rheumatoid arthritis that would cause this constellation of side effects. - This mechanism primarily affects **pyrimidine synthesis**, leading to DNA synthesis inhibition but is not characteristic of the likely drug here. *Inhibition of cyclooxygenase* - Inhibition of cyclooxygenase is the mechanism of action for **NSAIDs**, which are used for symptomatic relief in rheumatoid arthritis. - While NSAIDs can cause gastrointestinal side effects and kidney injury, they do not typically cause severe oral ulceration and liver enzyme elevations to this extent, especially not as a primary treatment. *Inhibition of inosine monophosphate dehydrogenase* - Inhibition of inosine monophosphate dehydrogenase is the mechanism of action for drugs like **mycophenolate mofetil**, which is an immunosuppressant used in transplant patients and for some autoimmune conditions. - While it has immunosuppressive effects and can cause gastrointestinal side effects, it's not a primary go-to for RA, and the described toxicity profile strongly points away from it. *Inhibition of NF-κB* - Inhibition of NF-κB is a mechanism associated with **glucocorticoids (corticosteroids)**, which are used to control inflammation in rheumatoid arthritis. - While corticosteroids have significant side effects, they do not typically cause the specific pattern of severe oral ulcers, elevated liver enzymes, and acute kidney injury as seen here.

Question 197: A 4-year-old boy is brought to the physician by his mother because of left-sided neck swelling that has slowly progressed over the past 4 weeks. He has no history of serious illness. Temperature is 38°C (100.4°F). Physical examination shows a non-tender, mobile mass in the left submandibular region with overlying erythema. A biopsy of the mass shows caseating granulomas. Pharmacotherapy with azithromycin and ethambutol is initiated. This patient is most likely to experience which of the following adverse effects related to ethambutol use?

A. Orange urine
B. Color blindness (Correct Answer)
C. Acute kidney injury
D. Peripheral neuropathy
E. Methemoglobinemia

Explanation: ***Color blindness*** - **Ethambutol** is known to cause **optic neuritis**, which can manifest as **red-green color blindness**, blurred vision, or decreased visual acuity. - This adverse effect is dose-dependent and typically reversible upon discontinuation of the drug, but regular **ophthalmologic monitoring** is crucial. *Orange urine* - **Orange discoloration of urine** is a classic side effect of **rifampin**, another antitubercular drug, not ethambutol. - Rifampin can also stain tears, sweat, and other bodily fluids orange-red. *Acute kidney injury* - While drug-induced kidney injury can occur with many medications, **acute kidney injury** is not a primary or common adverse effect specifically associated with **ethambutol**. - Renal function should be monitored with many drugs, but direct nephrotoxicity is not typical for ethambutol. *Peripheral neuropathy* - **Peripheral neuropathy** is a well-known adverse effect of **isoniazid**, another first-line antitubercular agent. - This effect is due to **isoniazid-induced pyridoxine (vitamin B6) deficiency**, which is typically prevented by co-administration of vitamin B6. *Methemoglobinemia* - **Methemoglobinemia** is a rare but serious condition where iron in hemoglobin is oxidized, reducing oxygen delivery. - It is sometimes associated with drugs like **dapsone**, nitrates, or local anesthetics, but not typically with **ethambutol**.

Question 198: A 47-year-old woman with a history of recent gastric bypass surgery presents for a follow-up visit. 8 months ago, she underwent gastric bypass surgery because she was struggling with maintaining her BMI below 42 kg/m². She previously weighed 120 kg (265 lb), and now she weighs 74.8 kg (165 lb). She says that she has low energy and is easily fatigued. These symptoms have become progressively worse over the past month. She is struggling to get through the day and sometimes has to nap before she can continue with her work. She has also recently noticed that she gets cramps in her legs, especially after a long day. The patient is afebrile and vital signs are within normal limits. Physical examination is unremarkable. Her hemoglobin is 9.5 mg/dL with an MCV of 75 fl. Her peripheral smear is shown in the exhibit. Which of the following supplements would most likely improve this patient’s symptoms?

A. Retinoids
B. Pyridoxine
C. Methylcobalamin
D. Calcium
E. Iron (Correct Answer)

Explanation: ***Iron*** - The patient's symptoms of **fatigue**, **low energy**, and **cramps**, along with a **low hemoglobin (9.5 mg/dL)** and **low MCV (75 fL)**, are highly suggestive of **iron deficiency anemia**. - **Gastric bypass surgery** often leads to **iron malabsorption** due to reduced gastric acid secretion and bypass of the duodenum, the primary site of iron absorption. *Retinoids* - **Retinoids (Vitamin A)** are essential for vision, immune function, and skin health. - Deficiency typically causes **night blindness** and **xerophthalmia**, not anemia or fatigue and cramps. *Pyridoxine* - **Pyridoxine (Vitamin B6)** is crucial for amino acid metabolism and neurotransmitter synthesis. - Deficiency can cause **sideroblastic anemia** (which is usually macrocytic or normocytic, not microcytic like in this case) and **neuropathy**, but it's not the primary cause of this patient's microcytic anemia. *Methylcobalamin* - **Methylcobalamin (Vitamin B12)** deficiency often occurs after gastric bypass due to the loss of **intrinsic factor**. - However, B12 deficiency causes **macrocytic anemia** (high MCV), not the **microcytic anemia** (low MCV) seen in this patient. *Calcium* - **Calcium** is vital for bone health, muscle function, and nerve transmission. - Deficiency can lead to **osteoporosis**, **tetany**, or **muscle cramps**, but it does not cause **microcytic anemia** or low hemoglobin.

Question 199: A 62-year-old man is brought to the emergency department from a senior-care facility after he was found with a decreased level of consciousness and fever. His personal history is relevant for colorectal cancer that was managed with surgical excision of the tumor. Upon admission, he is found to have a blood pressure of 130/80 mm Hg, a pulse of 102/min, a respiratory rate of 20/min, and a body temperature 38.8°C (101.8°F). There is no rash on physical examination; he is found to have neck rigidity, confusion, and photophobia. There are no focal neurological deficits. A head CT is normal without mass or hydrocephalus. A lumbar puncture was performed and cerebrospinal fluid (CSF) is sent to analysis while ceftriaxone and vancomycin are started. Which of the following additional antimicrobials should be added in the management of this patient?

A. Trimethoprim-sulfamethoxazole (TMP-SMX)
B. Ampicillin (Correct Answer)
C. Amphotericin
D. Meropenem
E. Clindamycin

Explanation: ***Ampicillin*** - This patient is a 62-year-old, indicating an increased risk for **Listeria monocytogenes** meningitis, which is typically susceptible to ampicillin. - Given his age and presentation with **meningeal signs** and fever, empirical coverage for Listeria with ampicillin is crucial, especially before CSF culture results are known. *Trimethoprim-sulfamethoxazole (TMP-SMX)* - While TMP-SMX can cover Listeria, it is generally considered a **second-line agent** for severe infections like meningitis due to slower bactericidal activity and potential for higher rates of treatment failure compared to ampicillin. - Ampicillin is the **preferred first-line treatment** for Listeria meningitis unless there is a specific contraindication. *Amphotericin* - Amphotericin is an **antifungal agent** used for fungal meningitis. - Although fungemia can occur in immunocompromised individuals or those with indwelling catheters, the initial presentation with bacterial meningitis symptoms and absence of specific risk factors for fungal infection do not support its empirical use. *Meropenem* - Meropenem is a **carbapenem** with a broad spectrum of activity, including many gram-negative and gram-positive bacteria, and some anaerobes. - While it has good CNS penetration and could cover some organisms like penicillin-resistant S. pneumoniae or gram-negative rods, it is not the primary empirical choice specifically for **Listeria monocytogenes**, and there's no indication for its broad-spectrum coverage over standard empirical therapy currently. *Clindamycin* - Clindamycin is primarily active against **gram-positive bacteria**, especially anaerobes and some staphylococci and streptococci. - It has **poor penetration into the CNS** and is therefore not effective for meningitis treatment, especially for common bacterial pathogens or Listeria.

Question 200: A 72-year-old man has been recently diagnosed with stage 3 squamous cell carcinoma of the oral cavity. After the necessary laboratory workup, concurrent chemoradiation therapy has been planned. Radiation therapy is planned to take place over 7 weeks and he will receive radiation doses daily, Monday–Friday, in 2.0 Gy fractions. For concurrent chemotherapy, he will receive intravenous cisplatin at a dosage of 50 mg/m2 weekly for 7 weeks. Which of the following best explains the mechanism of action of the antineoplastic drug that the patient will receive?

A. Free radical-mediated lipid peroxidation
B. Inhibition of polymerization of tubulin
C. Inhibition of topoisomerase 1
D. Inhibition of topoisomerase 2
E. Formation of interstrand DNA cross-links (Correct Answer)

Explanation: ***Formation of interstrand DNA cross-links*** - **Cisplatin** is a **platinum-based chemotherapeutic agent** that acts by forming **interstrand and intrastrand DNA cross-links**. - These cross-links interfere with **DNA replication and transcription**, leading to **DNA damage** and ultimately **apoptosis** in cancer cells. *Free radical-mediated lipid peroxidation* - While some chemotherapeutic agents, like **anthracyclines**, can induce **free radical formation** and subsequent damage, this is not the primary mechanism of action for cisplatin. - **Lipid peroxidation** primarily affects cell membranes, whereas cisplatin's main target is DNA. *Inhibition of polymerization of tubulin* - This mechanism of action is characteristic of **vinca alkaloids** (e.g., vincristine, vinblastine) and **taxanes** (e.g., paclitaxel, docetaxel), which disrupt microtubule formation and function. - Cisplatin does not target **tubulin polymerization**. *Inhibition of topoisomerase 1* - **Topoisomerase 1 inhibitors** such as **irinotecan** and **topotecan** prevent DNA unwinding by stabilizing the cleavable complex, leading to DNA breaks. - This is not how cisplatin exerts its therapeutic effects. *Inhibition of topoisomerase 2* - **Topoisomerase 2 inhibitors** like **etoposide** and **doxorubicin** interfere with DNA replication and repair by preventing the religation of DNA strands. - Cisplatin's mechanism is distinct from topoisomerase inhibition.

Question 201: A 66-year-old man comes to the physician because of a 3-month history of constipation and streaks of blood in his stool. He has had a 10-kg (22-lb) weight loss during this period. Colonoscopy shows an exophytic tumor in the sigmoid colon. A CT scan of the abdomen shows liver metastases and enlarged mesenteric and para-aortic lymph nodes. A diagnosis of stage IV colorectal cancer is made, and palliative chemotherapy is initiated. The chemotherapy regimen includes a monoclonal antibody that inhibits tumor growth by preventing ligand binding to a protein directly responsible for epithelial cell proliferation and organogenesis. Which of the following proteins is most likely inhibited by this drug?

A. VEGF
B. TNF-α
C. EGFR (Correct Answer)
D. ALK
E. CD52

Explanation: ***EGFR*** - The description of a monoclonal antibody preventing ligand binding to a protein responsible for **epithelial cell proliferation** and organogenesis strongly points to the **epidermal growth factor receptor (EGFR)**. - EGFR is highly expressed in many colorectal cancers and its activation by ligands like EGF promotes cell growth, survival, and metastasis. Inhibiting it reduces tumor progression. *VEGF* - **Vascular endothelial growth factor (VEGF)** is primarily involved in **angiogenesis**, the formation of new blood vessels. - While anti-VEGF therapies (e.g., bevacizumab) are used in colorectal cancer, their mechanism is inhibiting blood supply to the tumor, not directly blocking a receptor responsible for epithelial cell proliferation as described. *TNF-α* - **Tumor necrosis factor-alpha (TNF-α)** is a **cytokine** primarily involved in inflammation and immune responses. - Antibodies against TNF-α (e.g., infliximab) are used in inflammatory conditions like Crohn's disease, not typically as targeted therapy for colorectal cancer directly inhibiting epithelial proliferation. *ALK* - **Anaplastic lymphoma kinase (ALK)** is a **receptor tyrosine kinase** often implicated in lung cancer and lymphomas. - ALK rearrangements lead to oncogenic fusion proteins, but it is not a primary target for widespread epithelial cell proliferation in colorectal cancer. *CD52* - **CD52** is a glycoprotein found on the surface of various immune cells, including lymphocytes. - Antibodies targeting CD52 (e.g., alemtuzumab) are used in certain leukemias and lymphomas to deplete these cells, not for inhibiting epithelial cell proliferation in solid tumors.

Question 202: A 65-year-old male with diffuse large B cell lymphoma is treated with a chemotherapy regimen including 6-mercaptopurine. Administration of which of the following agents would increase this patient’s risk for mercaptopurine toxicity?

A. Allopurinol (Correct Answer)
B. Mesna
C. Leucovorin
D. Dexrazoxane
E. Amifostine

Explanation: ***Allopurinol*** - **Allopurinol** inhibits **xanthine oxidase**, an enzyme responsible for metabolizing **6-mercaptopurine (6-MP)** into inactive metabolites. - Concurrent administration significantly increases **6-MP levels**, leading to enhanced myelotoxicity and other severe adverse effects. *Mesna* - **Mesna** (2-mercaptoethane sulfonate) is a uroprotectant used to prevent **hemorrhagic cystitis** caused by oxazaphosphorine chemotherapy agents like **ifosfamide** and **cyclophosphamide**. - It does not interact with the metabolism of **6-mercaptopurine**. *Leucovorin* - **Leucovorin** (folinic acid) is a rescue agent for **methotrexate toxicity** and enhances the efficacy of **5-fluorouracil**. - It does not have a direct interaction with the metabolism or toxicity of **6-mercaptopurine**. *Dexrazoxane* - **Dexrazoxane** is a cardioprotective agent used to prevent **doxorubicin-induced cardiotoxicity**. - It does not interact with the metabolic pathways of **6-mercaptopurine**. *Amifostine* - **Amifostine** is a cytoprotective agent that reduces the toxicity of **cisplatin** and **radiation therapy** to normal tissues, particularly the kidneys and salivary glands. - It is not involved in the metabolism or potentiation of **6-mercaptopurine toxicity**.

Question 203: A 40-year-old woman comes to the physician for the evaluation of a 4-month history of reddening of the nose and cheeks. She has no itching or pain. She first noticed the redness while on a recent holiday in Spain, where she stayed at the beach and did daily wine tastings. She has tried several brands of sunscreen, stopped going outside in the middle of the day, and has not drunk alcohol since her trip, but the facial redness persists. She has no history of serious illness. Her younger sister has acne vulgaris, and her mother has systemic lupus erythematosus. The patient reports that she has had a lot of stress lately due to relationship problems with her husband. She does not smoke. Her vital signs are within normal limits. Examination shows erythema of the nose, chin, and medial cheeks with scant papules and telangiectasias. There are no comedones or blisters. The remainder of the examination shows no abnormalities. In addition to behavioral modifications, which of the following is the most appropriate initial treatment?

A. Topical corticosteroids
B. Topical metronidazole (Correct Answer)
C. Oral isotretinoin
D. Oral hydroxychloroquine
E. Topical benzoyl peroxide

Explanation: ***Topical metronidazole*** - This patient presents with **rosacea**, characterized by persistent facial erythema, papules, and telangiectasias, without comedones, which are typical of acne. **Topical metronidazole** is a first-line treatment for the inflammatory papules and pustules of rosacea. - It has both **anti-inflammatory** and **antibacterial properties** that are effective in controlling the symptoms of rosacea, particularly for mild to moderate cases. *Topical corticosteroids* - While topical corticosteroids can reduce inflammation, their use in rosacea is generally **contraindicated** as they can worsen the condition, leading to **steroid-induced rosacea**, telangiectasias, and skin atrophy with prolonged use. - They provide only temporary relief and can cause a rebound flare upon discontinuation. *Oral isotretinoin* - **Oral isotretinoin** is a potent retinoid primarily used for **severe, recalcitrant nodulocystic acne vulgaris** that has not responded to other treatments. - It is generally reserved for severe forms of rosacea (e.g., phymatous rosacea) or severe papulopustular rosacea unresponsive to topical therapies due to its significant side effects. *Oral hydroxychloroquine* - **Oral hydroxychloroquine** is an antimalarial drug with immunomodulatory properties, primarily used to treat **lupus** and **rheumatoid arthritis**. - There is no evidence to support its use as an initial treatment for rosacea. *Topical benzoyl peroxide* - **Topical benzoyl peroxide** is an antimicrobial agent effective for **acne vulgaris** due to its ability to kill *Cutibacterium acnes* and reduce comedones. - It is generally not recommended for rosacea as it can be **irritating** and worsen the erythema and sensitivity characteristic of rosacea, and it does not specifically address the underlying inflammation.

Question 204: A 49-year-old man presents with an 11-month history of progressive fatigue. He denies any night sweats, weight loss, abdominal pain, nausea, vomiting, change in bowel habits, or bleeding. He has no significant past medical history. His vital signs include: temperature 37.0°C (98.6°F), blood pressure 119/81 mm Hg, pulse 83/min, and respiratory rate 19/min. On physical examination, mild splenomegaly is noted on abdominal percussion. Laboratory findings are significant for a leukocyte count of 16,700/mm3 and a low serum leukocyte alkaline phosphatase (LAP) score. A bone marrow biopsy is performed, which shows marked hypercellularity with a clear dominance of granulocytes. Cytogenetic analysis is positive for the Ph1 gene. Which of the following is the best course of treatment for this patient?

A. Cytarabine
B. Interferon-α-2b
C. Rituximab
D. Imatinib (Correct Answer)
E. Hydroxyurea

Explanation: ***Imatinib*** - This patient's presentation with **fatigue**, **splenomegaly**, **leukocytosis** with granulocytic dominance, **low LAP score**, and the presence of the **Ph1 gene (BCR-ABL fusion)** is highly characteristic of **Chronic Myeloid Leukemia (CML)**. - **Imatinib** is a **tyrosine kinase inhibitor (TKI)** that specifically targets the **BCR-ABL fusion protein**, which drives CML, making it the first-line and best course of treatment. *Cytarabine* - **Cytarabine** is primarily used in the treatment of **acute myeloid leukemia (AML)**, not CML, and works by interfering with DNA synthesis. - While it can be used in some aggressive leukemias, it is not the targeted therapy for CML's specific genetic abnormality. *Interferon-α-2b* - **Interferon-α-2b** was an earlier treatment for CML but has largely been replaced by **TKIs** like imatinib due to its significantly higher toxicity and lower efficacy. - It works by modulating the immune system and inhibiting cell proliferation but lacks the specificity of TKIs. *Rituximab* - **Rituximab** is a **monoclonal antibody** targeting the **CD20 antigen** found on B-lymphocytes. - It is used in the treatment of **B-cell non-Hodgkin lymphomas** and **chronic lymphocytic leukemia (CLL)**, which are distinct from CML. *Hydroxyurea* - **Hydroxyurea** is a **cytoreductive agent** used to control high white blood cell counts in CML, offering symptomatic relief by reducing tumor burden. - However, it does not target the underlying genetic abnormality (BCR-ABL) and is therefore a supportive measure, not the definitive treatment and can be given as preparatory to the main treatment, which in this case is imatinib.

Question 205: A 20-year-old college student is brought to the ED after a motor vehicle accident. Primary and secondary surveys reveal no significant compromise to his airway, his cardiovascular system, or to his motor function. However, his conjunctiva appear injected and he maintains combative behavior towards staff. What is the gold standard confirmatory test for substance use?

A. Gas chromatography / mass spectrometry (GC/MS) (Correct Answer)
B. Urine immunoassay
C. Western blot
D. Breath alcohol test
E. Polymerase chain reaction

Explanation: ***Gas chromatography / mass spectrometry (GC/MS)*** - **GC/MS** is considered the **gold standard** for confirming substance use due to its high specificity and sensitivity in identifying and quantifying various substances. - It effectively separates individual compounds in a complex mixture and identifies them based on their unique mass spectra, making it highly reliable for forensic and clinical toxicology. *Urine immunoassay* - **Urine immunoassays** are typically used as **screening tests** for substances because they are rapid and relatively inexpensive, but they can produce false positives. - While useful for initial detection, they require confirmatory testing, often by GC/MS, due to their lower specificity. *Western blot* - **Western blot** is primarily used to detect **specific proteins** in a sample, especially in the diagnosis of infectious diseases or autoimmune conditions, not for substance identification. - It involves separating proteins by gel electrophoresis and then transferring them to a membrane for antibody-based detection. *Breath alcohol test* - A **breath alcohol test** is specifically designed to measure **alcohol concentration** in the breath, which correlates with blood alcohol content. - It is not used for detecting other illicit substances and would not provide a comprehensive toxicology profile. *Polymerase chain reaction* - **Polymerase chain reaction (PCR)** is a molecular biology technique used to amplify **DNA or RNA sequences**, primarily for detecting genetic material from pathogens or for genetic analysis. - It has no role in the direct detection of drugs or their metabolites in biological samples.

Question 206: A hospitalized 45-year-old man has had mild flank pain since awakening 3 hours ago. He also reports a new generalized rash. Two weeks ago, he was diagnosed with pulmonary tuberculosis. Current medications include isoniazid, pyrazinamide, rifampin, ethambutol, and pyridoxine. His temperature is 38.3°C (100.9°F), pulse is 74/min, and blood pressure is 128/72 mm Hg. Examination of the skin shows diffuse erythema with confluent papules. There is no costovertebral angle tenderness. Laboratory studies show: Leukocyte count 9,800/mm3 Segmented neutrophils 59% Bands 3% Eosinophils 4% Lymphocytes 29% Monocytes 5% Serum Urea nitrogen 25 mg/dL Creatinine 1.9 mg/dL Urine WBC 8–10/hpf Eosinophils numerous RBC 5–6/hpf RBC casts negative WBC casts numerous In addition to intravenous fluid resuscitation, which of the following is the most appropriate next step in management?

A. Perform renal biopsy
B. Initiate hemodialysis
C. Discontinue rifampin (Correct Answer)
D. Perform serum protein electrophoresis
E. Administer ciprofloxacin

Explanation: ***Discontinue rifampin*** - The patient presents with **fever**, **rash**, **eosinophilia**, and **acute kidney injury** with **eosinophiluria** and **WBC casts**, which are classic signs of **acute interstitial nephritis (AIN)**. - Among the anti-tuberculosis medications, **rifampin** is the most common cause of drug-induced AIN, particularly when presenting with the classic triad of fever, rash, and acute kidney injury. - Discontinuing the offending agent is the most critical initial step in management of drug-induced AIN. *Perform renal biopsy* - A renal biopsy is generally reserved for cases where the diagnosis of **acute interstitial nephritis (AIN)** is unclear, or if there is no improvement after discontinuing the suspected drug and initiating corticosteroids. - Given the clear clinical picture and classic laboratory findings, the immediate priority is to remove the likely causative agent rather than perform an invasive procedure. *Initiate hemodialysis* - Hemodialysis is indicated for patients with severe **acute kidney injury (AKI)** evidenced by intractable electrolyte imbalances, severe fluid overload, or uremic symptoms. - Though the patient has **elevated creatinine (1.9 mg/dL)**, there is no indication of immediately life-threatening complications that would warrant urgent dialysis at this stage. *Perform serum protein electrophoresis* - Serum protein electrophoresis is used to diagnose conditions like **multiple myeloma**, which can cause **kidney disease (myeloma kidney)**. - The patient's presentation with **fever, rash, eosinophilia**, and **WBC casts** is inconsistent with myeloma kidney, making this investigation less relevant than addressing the suspected drug-induced AIN. *Administer ciprofloxacin* - The patient's symptoms are highly suggestive of **drug-induced acute interstitial nephritis (AIN)**, an allergic reaction, rather than an infection. - There is no clinical or laboratory evidence (e.g., specific infectious markers) to support the use of an antibiotic like ciprofloxacin, which could potentially worsen kidney function or cause further drug interactions.

Question 207: A 36-year-old male with fluctuating levels of consciousness is brought to the emergency department by ambulance due to a fire in his home. He currently opens his eyes to voice, localizes painful stimuli, responds when asked questions, but is disoriented and cannot obey commands. The patient’s temperature is 99°F (37.2°C), blood pressure is 86/52 mmHg, pulse is 88/min, and respirations are 14/min with an oxygen saturation of 97% O2 on room air. Physical exam shows evidence of soot around the patient’s nose and mouth, but no burns, airway obstruction, nor accessory muscle use. A blood lactate is 14 mmol/L. The patient is started on intravenous fluids. What is the next best step in management?

A. Methylene blue
B. Hyperbaric oxygen
C. Sodium thiosulfate and sodium nitrite
D. Intravenous epinephrine
E. 100% oxygen, hydroxycobalamin, and sodium thiosulfate (Correct Answer)

Explanation: ***100% oxygen, hydroxycobalamin, and sodium thiosulfate*** - This patient presents with signs of both **carbon monoxide poisoning** (fire exposure, disoriented, altered mental status) and **cyanide poisoning** (fire exposure, very high lactate, normal oxygen saturation despite altered mental status). This combination therapy directly addresses both. - **100% oxygen** competes with carbon monoxide for hemoglobin binding and helps clear it, while **hydroxycobalamin** and **sodium thiosulfate** are antidotes for cyanide poisoning, converting cyanide into less toxic compounds. *Methylene blue* - **Methylene blue** is used to treat **methemoglobinemia**, a condition where iron in hemoglobin is oxidized, leading to impaired oxygen transport. - The patient's symptoms (fire exposure, altered mental status, and a high lactate with normal SpO2) are not characteristic of methemoglobinemia, but rather strong indicators of carbon monoxide and cyanide poisoning. *Hyperbaric oxygen* - **Hyperbaric oxygen** is a treatment for severe carbon monoxide poisoning, but it is not the initial or sole treatment for a patient with suspected co-existing cyanide poisoning. - While recommended for **severe CO poisoning**, it doesn't directly address cyanide toxicity, which is suggested by the metabolic acidosis with a high lactate level despite normal oxygen saturation. *Sodium thiosulfate and sodium nitrite* - This combination (the **Lilly kit**) is traditionally used to treat **cyanide poisoning**, with sodium nitrite inducing methemoglobinemia to sequester cyanide, and sodium thiosulfate aiding its excretion. - The patient also requires treatment for **carbon monoxide poisoning**, and hydroxycobalamin is generally preferred over sodium nitrite as it does not induce methemoglobinemia, which can worsen hypoxia in CO poisoning. *Intravenous epinephrine* - **Epinephrine** is a powerful vasoconstrictor and bronchodilator primarily used to treat **anaphylaxis** or **cardiac arrest**. - There is no indication of anaphylaxis or cardiac arrest in this patient, and epinephrine would not be an appropriate treatment for carbon monoxide or cyanide poisoning.

Question 208: A 62-year-old woman presents with abdominal pain and blood in her urine. Since the acute onset of symptoms 3 days ago, there has been no improvement. She describes the pain as moderate, sharp and burning in character, non-radiating, and localized to the suprapubic region. She also has noted some mild urinary frequency and urgency for the past 5 days, which has been getting progressively worse. She denies any flank pain, fever, chills, night sweats, dysuria, or pain on urination. The patient has a history of an abdominal leiomyosarcoma, which was diagnosed 6 months ago. The course of her disease is complicated by hepatic metastases, for which she recently started receiving a new therapy. The patient reports a 15-pack-year smoking history, but no alcohol or recreational drug use. Her temperature is 37.0℃ (98.6℉), pulse is 84/min, respiratory rate is 18/min, and blood pressure is 110/75 mm Hg. On physical examination, there is some mild suprapubic tenderness to palpation. The remainder of the exam is unremarkable. Laboratory findings include a mild leukopenia of 3,000/mm3. A urine dipstick reveals 3+ blood. Which of the following best describes the medication that could have prevented this patient’s symptoms?

A. Antifolate that inhibits dihydrofolate reductase, inhibiting purine production necessary for cell synthesis and division
B. Serine protease inhibitor that reduces the action of plasmin
C. A thiol given concurrently with an antineoplastic agent to help reduce inflammation of the transitional epithelium of the bladder (Correct Answer)
D. Agent that binds to an intracellular receptor and results in the transactivation of genes that promote gluconeogenesis and has anti-inflammatory effects
E. Small molecule tyrosine kinase inhibitor that inhibits bcr-abl tyrosine kinase, blocking cell proliferation and inducing apoptosis

Explanation: ***A thiol given concurrently with an antineoplastic agent to help reduce inflammation of the transitional epithelium of the bladder*** - This patient's symptoms (suprapubic pain, hematuria, urinary frequency, urgency, and leukopenia) are consistent with **hemorrhagic cystitis**, a known complication of **cyclophosphamide** (an antineoplastic agent) or ifosfamide therapy. - **Mesna** (2-mercaptoethane sulfonate sodium) is a thiol compound administered with cyclophosphamide to detoxify its urotoxic metabolite, **acrolein**, thereby preventing hemorrhagic cystitis. *Antifolate that inhibits dihydrofolate reductase, inhibiting purine production necessary for cell synthesis and division* - This describes **methotrexate**, an antineoplastic agent that can cause nephrotoxicity and mucositis but is not primarily associated with hemorrhagic cystitis prevented by mesna. - **Leucovorin** is the rescue medication given with methotrexate to reduce toxicity, not mesna. *Serine protease inhibitor that reduces the action of plasmin* - This describes antifibrinolytic agents like **tranexamic acid** or aminocaproic acid, which are used to prevent or treat bleeding by inhibiting fibrinolysis. - While these might be used to manage severe bleeding, they do not prevent chemical irritation and inflammation of the bladder lining caused by chemotherapeutic agents. *Agent that binds to an intracellular receptor and results in the transactivation of genes that promote gluconeogenesis and has anti-inflammatory effects* - This describes **glucocorticoids** (e.g., prednisone, dexamethasone), which are anti-inflammatory and immunosuppressive agents. - Glucocorticoids are not used to prevent hemorrhagic cystitis caused by cyclophosphamide, and their mechanism of action is distinctly different from mesna. *Small molecule tyrosine kinase inhibitor that inhibits bcr-abl tyrosine kinase, blocking cell proliferation and inducing apoptosis* - This describes **imatinib** or other BCR-ABL inhibitors used primarily in chronic myeloid leukemia (CML). - This type of medication and its associated toxicities are unrelated to the patient's symptoms or the protective role of mesna.

Question 209: A 38-year-old woman presents to her primary care physician for a new patient appointment. She states that she feels well and has no current complaints. The patient recently started seeing a specialist for treatment for another medical condition but otherwise has had no medical problems. The patient lives alone and drinks 2 alcoholic beverages every night. She has had 3 sexual partners in her lifetime, uses oral contraceptive pills for contraception, and has never been pregnant. Physical exam reveals a pleasant, obese woman with normal S1 and S2 on cardiac exam. Musculoskeletal exam reveals swelling of the MCP and PIP joints of the hands as well as ulnar deviation of the fingers. Laboratory tests are ordered and results are below: Serum: Na+: 139 mEq/L Cl-: 100 mEq/L K+: 4.3 mEq/L HCO3-: 25 mEq/L BUN: 20 mg/dL Glucose: 99 mg/dL Creatinine: 1.1 mg/dL Ca2+: 10.2 mg/dL AST: 95 U/L ALT: 68 U/L Which of the following best explains this patient's abnormal laboratory values?

A. Viral infection
B. Medication (Correct Answer)
C. Obesity
D. Bacterial infection
E. Alcohol

Explanation: ***Medication*** - The AST and ALT elevations, along with the patient's rheumatological findings (**MCP and PIP joint swelling**, **ulnar deviation**), strongly suggest **rheumatoid arthritis**. - A common treatment for rheumatoid arthritis is **methotrexate**, which is known to cause **elevated liver enzymes (AST, ALT)**. *Viral infection* - While viral infections can cause elevated transaminases, this patient presents with classic signs of **rheumatoid arthritis** without other typical symptoms of acute viral illness. - The chronic nature of joint changes (ulnar deviation) makes an acute viral etiology for the liver enzyme elevation less likely as the primary cause. *Obesity* - Obesity is a risk factor for **non-alcoholic fatty liver disease (NAFLD)**, which can cause elevated AST and ALT. - However, NAFLD typically causes more modest elevations, often with **ALT > AST**, and obesity alone does not explain the rheumatological findings. *Bacterial infection* - Bacterial infections can cause systemic inflammation and potentially affect liver enzymes, but this patient shows no signs of acute infection (e.g., fever, leukocytosis) and presents with chronic joint issues. - The pattern of joint involvement and liver enzyme elevation is not typical for a bacterial infection. *Alcohol* - Chronic alcohol consumption (2 drinks/night) can lead to **alcoholic liver disease** and elevated AST and ALT, typically with an **AST:ALT ratio of 2:1 or greater**. - While the patient drinks alcohol, the liver enzyme elevations are relatively mild, and her presentation also includes rheumatological symptoms that are not explained by alcohol alone; the AST:ALT ratio here is less than 2:1.

Question 210: A 67-year-old man comes to the physician for a follow-up examination after he was diagnosed with mantle cell lymphoma. The physician recommends a chemotherapeutic regimen containing bortezomib. Which of the following best describes the effect of this drug?

A. Crosslinking of purine bases
B. Preventing the relaxation of DNA supercoils
C. Inhibition of tyrosine kinase receptors
D. Accumulation of ubiquitinated proteins (Correct Answer)
E. Stabilization of tubulin polymers

Explanation: ***Accumulation of ubiquitinated proteins*** - **Bortezomib** is a **proteasome inhibitor**, specifically targeting the 26S proteasome, which is responsible for degrading ubiquitinated proteins. - Its inhibition leads to the accumulation of various **ubiquitinated proteins**, including pro-apoptotic factors, ultimately inducing **apoptosis** in cancer cells. *Crosslinking of purine bases* - This mechanism is characteristic of **alkylating agents** such as cyclophosphamide or cisplatin, which form covalent bonds with DNA, preventing replication and transcription. - **Bortezomib** does not directly crosslink DNA bases; its primary action is on protein degradation pathways. *Preventing the relaxation of DNA supercoils* - This describes the mechanism of **topoisomerase inhibitors**, such as etoposide (topoisomerase II) or irinotecan (topoisomerase I), which block DNA replication and repair. - Bortezomib has a distinct mechanism involving proteasome inhibition, not direct interaction with DNA or topoisomerases. *Inhibition of tyrosine kinase receptors* - This is the action of **tyrosine kinase inhibitors**, a class of drugs like imatinib or gefitinib, that target specific signaling pathways involved in cell growth and proliferation. - Bortezomib's anti-cancer effects are mediated through protein degradation pathways, not by inhibiting receptor tyrosine kinases. *Stabilization of tubulin polymers* - This mechanism is characteristic of **taxanes** (e.g., paclitaxel), which hyperstabilize microtubules, interfering with cell division. - **Bortezomib** does not affect microtubule dynamics; its action is focused on the proteasomal degradation system.

Question 211: A 55-year-old man with a history of fatigue and exertional dyspnea presents to the urgent care clinic following an acute upper respiratory illness. On physical examination, his pulses are bounding, his complexion is very pale, and scleral icterus is apparent. The spleen is moderately enlarged. Oxygen saturation is 79% at rest, with a new oxygen requirement of 9 L by a non-rebreather mask. Laboratory analysis results show a hemoglobin level of 6.8 g/dL. Of the following options, which hypersensitivity reaction does this condition represent?

A. Type III–immune complex-mediated hypersensitivity reaction
B. Type I–anaphylactic hypersensitivity reaction
C. Type IV–cell-mediated (delayed) hypersensitivity reaction
D. Type II–cytotoxic hypersensitivity reaction (Correct Answer)
E. Type II and III–mixed cytotoxic and immune complex hypersensitivity reaction

Explanation: ***Type II–cytotoxic hypersensitivity reaction*** - The patient's symptoms, including **fatigue**, **exertional dyspnea**, **pale complexion**, **scleral icterus**, and **splenomegaly**, along with a **low hemoglobin** of 6.8 g/dL, strongly suggest **hemolytic anemia**. - Following an **upper respiratory illness**, this presentation is consistent with **autoimmune hemolytic anemia (AIHA)**, where antibodies (mainly IgG or IgM) mistakenly target and destroy red blood cells, which is a classic example of a **Type II hypersensitivity reaction**. *Type III–immune complex-mediated hypersensitivity reaction* - This reaction involves the formation of **immune complexes** that deposit in tissues, leading to inflammation and damage, as seen in conditions like **serum sickness** or **lupus nephritis**. - The patient's primary symptoms of **hemolysis** and **anemia** are not characteristic of immune complex deposition. *Type I–anaphylactic hypersensitivity reaction* - This type involves **IgE-mediated mast cell degranulation**, leading to rapid onset symptoms like **urticaria**, **angioedema**, **bronchospasm**, and **hypotension**. - The patient's presentation of gradual onset fatigue, anemia, and icterus does not align with the acute, systemic allergic reaction seen in Type I hypersensitivity. *Type IV–cell-mediated (delayed) hypersensitivity reaction* - This reaction is mediated by **T cells** and **macrophages**, with a delayed onset (24-72 hours), as seen in **contact dermatitis** or **tuberculosis skin tests**. - The patient's rapid development of severe anemia and an acute hemolytic picture is not consistent with a T-cell-mediated delayed reaction. *Type II and III–mixed cytotoxic and immune complex hypersensitivity reaction* - While some autoimmune conditions can involve elements of both Type II and Type III reactions, the overwhelming clinical picture in this patient points to direct **antibody-mediated destruction of red blood cells (Type II)**. - There are no specific features mentioned, such as vasculitis or nephritis, that would strongly suggest **immune complex deposition** in addition to the prominent hemolytic anemia.

Question 212: A 56-year-old man of Nepalese origin presents to a clinic complaining of skin rashes that have been troubling him for years. On examination, there are numerous poorly demarcated skin lesions present on all parts of the body. There is also evidence of significant facial thickening, eyebrow loss, and symmetrical sensory neuropathy in a ‘glove and stocking’ distribution. An examination of the hands reveals bilateral weakness. A skin biopsy is taken from one of the lesions, and the culture is positive for acid-fast bacilli. Which of the following pharmacological therapies is involved in the treatment of this condition?

A. Ketoconazole
B. Isoniazid
C. Dapsone (Correct Answer)
D. Flucloxacillin
E. Prednisone

Explanation: ***Dapsone*** - The presented symptoms (poorly demarcated skin lesions, facial thickening, eyebrow loss, symmetrical sensory neuropathy in a 'glove and stocking' distribution, bilateral weakness, and acid-fast bacilli on skin biopsy) are characteristic of **lepromatous leprosy**. - **Dapsone** is a cornerstone medication in the multidrug therapy (MDT) for leprosy, commonly used in combination with rifampicin and clofazimine for 12 months in multibacillary disease. - This is the primary **antimicrobial agent** targeting *Mycobacterium leprae*. *Ketoconazole* - **Ketoconazole** is an antifungal medication, primarily used for superficial and systemic fungal infections. - It has no role in the treatment of leprosy, which is a bacterial infection caused by *Mycobacterium leprae*. *Isoniazid* - **Isoniazid** is a first-line antitubercular drug used to treat tuberculosis (TB). - While both leprosy and TB are caused by mycobacteria, they require different treatment regimens, and isoniazid is not used in standard leprosy therapy. *Flucloxacillin* - **Flucloxacillin** is an antibiotic from the penicillin class, primarily used to treat infections caused by **Staphylococcus** bacteria. - It is ineffective against *Mycobacterium leprae*, which requires specific antimycobacterial drugs. *Prednisone* - **Prednisone** is a corticosteroid used to reduce inflammation and suppress the immune system. - While corticosteroids like prednisone may be used as **adjunctive therapy** to manage acute inflammatory reactions (e.g., **Type 1 reversal reactions or Type 2 lepra reactions/ENL**) that can occur during leprosy treatment, they are not a primary antimicrobial therapy and do not directly kill *Mycobacterium leprae*.

Question 213: A 65-year-old female patient with a past medical history of diabetes mellitus and an allergy to penicillin develops an infected abscess positive for MRSA on the third day of her hospital stay. She is started on an IV infusion of vancomycin at a dose of 1000 mg every 12 hours. Vancomycin is eliminated by first-order kinetics and has a half life of 6 hours. The volume of distribution of vancomycin is 0.5 L/kg. Assuming no loading dose is given, how long will it take for the drug to reach 94% of its plasma steady state concentration?

A. 30 hours
B. 12 hours
C. 6 hours
D. 18 hours
E. 24 hours (Correct Answer)

Explanation: ***24 hours*** - For a drug eliminated by **first-order kinetics**, it takes approximately **4 half-lives** to reach **93.75%** of steady state concentration, which is conventionally rounded to **94%**. - Since the half-life of vancomycin is **6 hours**, reaching 94% of steady state requires: 4 × 6 hours = **24 hours**. - This follows the pharmacokinetic principle that each half-life brings the drug closer to steady state: 1 t½ = 50%, 2 t½ = 75%, 3 t½ = 87.5%, 4 t½ = 93.75%. *30 hours* - This duration represents **five half-lives** (5 × 6 hours), at which point approximately **96.875%** (often rounded to 97%) of steady state would be reached. - This exceeds the 94% target specified in the question. *18 hours* - This duration represents **three half-lives** (3 × 6 hours), at which point approximately **87.5%** of steady state concentration would be reached. - This falls short of the 94% target. *12 hours* - This duration represents **two half-lives** (2 × 6 hours), at which point approximately **75%** of steady state concentration would be reached. - This is insufficient time to reach 94% of plasma steady state concentration. *6 hours* - This duration represents **one half-life**, at which point approximately **50%** of steady state concentration would be reached. - This is far too short to achieve near-steady state levels.

Question 214: A 55-year-old man presents to the urgent clinic complaining of pain in his right foot. He reported that the pain is intense that he had to remove his shoe and sock, and rates the pain level as 6 out of 10. He does not report trauma or recent infection. The past medical history includes hypertension. The medications include hydrochlorothiazide, enalapril, and a daily multivitamin. The family history is noncontributory. He consumes alcohol in moderation. His diet mostly consists of red meat and white rice. The blood pressure is 137/85 mm Hg, heart rate is 74/min, respiratory rate is 12/min, and the temperature is 36.9°C (98.4°F). The physical examination demonstrates swelling, redness, and tenderness to palpation in the first metatarsophalangeal joint of his right foot. There are no skin lesions. The rest of the patient’s examination is normal. An arthrocentesis procedure is scheduled. Which of the following is the most likely pharmacological treatment for the presented patient?

A. Diclofenac alone (Correct Answer)
B. Allopurinol alone
C. Probenecid alone
D. Colchicine and celecoxib
E. Oral methylprednisolone and meloxicam

Explanation: - ***Diclofenac alone*** - This patient presents with a classic picture of **acute gout**: sudden onset of severe pain, swelling, redness, and tenderness in the **first metatarsophalangeal joint** (podagra), with a history of hypertension and diuretic use (hydrochlorothiazide), and a diet rich in red meat. - **NSAIDs like diclofenac** are first-line treatment for acute gout attacks, as they effectively reduce pain and inflammation. - *Allopurinol alone* - **Allopurinol** is a **xanthine oxidase inhibitor** used for the **long-term prevention** of gout attacks by lowering uric acid levels. It is not indicated for the management of acute flare-ups. - Initiating allopurinol during an acute attack can paradoxically **worsen the flare** by mobilizing uric acid crystals. - *Probenecid alone* - **Probenecid** is a **uricosuric agent** that increases uric acid excretion via the kidneys and is used for **long-term management** of gout in patients who are underexcretors of uric acid. - Like allopurinol, it is **not used for acute gout attacks** and should not be initiated during a flare. - *Colchicine and celecoxib* - **Colchicine** is an effective treatment for acute gout, particularly if given within the first 24-36 hours of symptom onset, but it can cause **significant gastrointestinal side effects** (nausea, vomiting, diarrhea). - **Celecoxib** is a **COX-2 selective NSAID** which is also effective in acute gout. However, combining colchicine with another NSAID like celecoxib for initial treatment might be an **overkill** in terms of side effects and typically **only one first-line agent (NSAID or colchicine) is sufficient.** - *Oral methylprednisolone and meloxicam* - **Oral methylprednisolone (corticosteroids)** are highly effective for acute gout, especially in patients with **contraindications to NSAIDs** or who have polyarticular involvement. - **Meloxicam** is an NSAID, and while appropriate for acute gout, combining it with systemic corticosteroids (methylprednisolone) is **usually reserved for more severe cases** or when monotherapy is insufficient, due to increased risk of side effects.

Question 215: A 60-year-old man comes to the physician because of a 2-day history of blood in his urine, lower abdominal pain, and a burning sensation while micturating. Five months ago, he was diagnosed with high-grade non-Hodgkin lymphoma and a deep vein thrombosis of his right popliteal vein. His medications include polychemotherapy every 3 weeks and a daily subcutaneous dose of low molecular weight heparin. The last cycle of chemotherapy was 2 weeks ago. His temperature is 37°C (98.6°F), pulse is 94/min, and blood pressure is 110/76 mm Hg. Examination shows bilateral axillary and inguinal lymphadenopathy, hepatosplenomegaly, and mild suprapubic tenderness. Laboratory studies show: Hemoglobin 10.2 g/dL Leukocytes 4,300/mm3 Platelet count 145,000/mm3 Partial thromboplastin time 55 seconds Prothrombin time 11 seconds (INR=1) Urine RBCs 50–55/hpf RBC casts negative WBCs 7/hpf Epithelial cells 5/hpf Bacteria occasional Administration of which of the following is most likely to have prevented this patient's current condition?

A. Ciprofloxacin
B. Palifermin
C. Mercaptoethane sulfonate (Correct Answer)
D. Protamine sulfate
E. Dexrazoxane

Explanation: ***Mercaptoethane sulfonate*** - The patient's symptoms of **hematuria**, **lower abdominal pain**, and **dysuria** in the context of recent chemotherapy strongly suggest **hemorrhagic cystitis**. This is a known side effect of cyclophosphamide (or ifosfamide), which is often part of polychemotherapy for lymphoma. - **Mercaptoethane sulfonate (MESNA)** is a chemoprotectant specifically used to detoxify the urotoxic metabolites (acrolein) of cyclophosphamide and ifosfamide, thereby preventing hemorrhagic cystitis. *Ciprofloxacin* - **Ciprofloxacin** is an antibiotic used to treat bacterial infections, particularly urinary tract infections. While the patient has some WBCs and occasional bacteria in his urine, his primary condition is most likely drug-induced hemorrhagic cystitis, not a bacterial UTI that would be prevented by ciprofloxacin. - The context of recent chemotherapy points away from a primary bacterial infection as the cause of hematuria. *Palifermin* - **Palifermin** is a recombinant human keratinocyte growth factor used to prevent and treat **oral mucositis**, a common side effect of chemotherapy and radiation. - It does not have any protective effect against hemorrhagic cystitis. *Protamine sulfate* - **Protamine sulfate** is used to reverse the anticoagulant effects of **heparin** and **low molecular weight heparin (LMWH)**. While the patient is on LMWH, the hematuria is more likely due to chemotherapy-induced cystitis rather than LMWH overdose, as his platelet count is reasonable and he has no other signs of widespread bleeding attributable to LMWH. - Administering protamine sulfate would not prevent hemorrhagic cystitis. *Dexrazoxane* - **Dexrazoxane** is a cardioprotective agent used to reduce the incidence and severity of **anthracycline-induced cardiotoxicity** (e.g., from doxorubicin). - It does not prevent or treat hemorrhagic cystitis caused by cyclophosphamide or ifosfamide.

Question 216: A 45-year-old woman presents to the office complaining of fatigue and unintentional weight loss. On examination, there is a palpable firm lymph node in the cervical area. Biopsy of the lymph node reveals Hodgkin’s lymphoma. The patient agrees to start the standard chemotherapy regimen. A few months later, after the completion of 3 successful courses, the patient presents with a dry cough and progressively worsening shortness of breath. Her temperature is 37°C (98.6°F), the blood pressure is 110/70 mm Hg, the pulse is 72/min, and the respirations are 16/min. Pulse oximetry shows an O2 saturation of 94% on room air. On spirometry, the patient's FEV1/FVC ratio is normal. Chest CT reveals bilateral diffuse cystic airspaces in middle and lower lung fields. Which of the following is the most likely cause of this patient’s current symptoms?

A. Transfusion-related acute lung injury
B. Metastatic spread to the lungs
C. Development of bacterial pneumonia due to immunocompromised state
D. Drug-induced interstitial lung disease (Correct Answer)
E. Development of chronic obstructive pulmonary disease

Explanation: ***Drug-induced interstitial lung disease*** - The patient's symptoms of **dry cough**, **dyspnea**, and **hypoxemia** after chemotherapy for Hodgkin's lymphoma, along with CT findings of **diffuse cystic airspaces**, are highly suggestive of **drug-induced interstitial lung disease**. Chemotherapeutic agents like **bleomycin** are well-known causes of such pulmonary fibrosis. - **Normal FEV1/FVC ratio** with worsening shortness of breath and hypoxemia points towards a **restrictive lung disease** pattern, which is characteristic of interstitial lung diseases. *Transfusion-related acute lung injury* - **TRALI** typically presents acutely, within 6 hours of a blood transfusion, with severe hypoxemia and bilateral pulmonary infiltrates. - The patient’s symptoms developed over "a few months" and are not directly linked to a recent transfusion. *Metastatic spread to the lungs* - While Hodgkin's lymphoma can metastasize to the lungs, it typically presents with nodules or masses on CT scan, not diffuse cystic changes. - The primary concern here is not recurrence, especially given the history of successful chemotherapy courses. *Development of bacterial pneumonia due to immunocompromised state* - Bacterial pneumonia usually presents with fever, productive cough, and lobar or patchy consolidations on CT, often with an elevated white blood cell count. - The patient's temperature is normal, and CT findings are not typical for bacterial pneumonia but rather for chronic interstitial changes. *Development of chronic obstructive pulmonary disease* - COPD is characterized by a **reduced FEV1/FVC ratio** and usually a history of smoking or chronic exposure to irritants, and predominantly causes emphysema or chronic bronchitis. - The patient has a normal FEV1/FVC ratio and CT findings of cystic airspaces rather than typical emphysema.

Question 217: A 65-year-old man comes to the physician for a routine health maintenance examination. He feels well. His most recent examination 2 years ago included purified protein derivative (PPD) skin testing and showed no abnormalities. He is a retired physician and recently came back from rural China where he completed a voluntary service at a local healthcare center. A PPD skin test is performed. Three days later, an induration of 12 mm is noted. An x-ray of the chest shows no abnormalities. He is started on a drug that inhibits the synthesis of mycolic acid. This patient is at greatest risk of developing which of the following adverse effects?

A. Cytochrome P-450 induction
B. Hyperuricemia
C. Liver injury (Correct Answer)
D. Optic neuropathy
E. Nephrotoxicity

Explanation: ***Liver injury*** - The drug described is **isoniazid**, which inhibits **mycolic acid synthesis** and is first-line treatment for **latent tuberculosis infection**. - **Isoniazid-induced hepatotoxicity** is the most significant adverse effect, with risk increasing dramatically in patients **>35 years old** (this patient is 65). - Additional risk factors include alcohol use, pre-existing liver disease, and concurrent hepatotoxic medications. - Patients should be monitored with baseline and periodic liver function tests. *Cytochrome P-450 induction* - **Rifampin**, not isoniazid, is a potent **CYP450 inducer** that decreases levels of many co-administered drugs. - Isoniazid is actually a **CYP450 inhibitor** (inhibits CYP2C19, CYP3A4), which can increase levels of other drugs like phenytoin and warfarin. *Hyperuricemia* - **Pyrazinamide** is the anti-tuberculosis drug that causes **hyperuricemia** by inhibiting renal tubular secretion of uric acid. - This can precipitate acute gout attacks in susceptible patients. - Isoniazid does not affect uric acid metabolism. *Optic neuropathy* - **Ethambutol** causes dose-dependent **optic neuropathy**, presenting with decreased visual acuity and **red-green color blindness**. - Patients on ethambutol require baseline and monthly visual assessments. - Isoniazid is not associated with optic toxicity. *Nephrotoxicity* - **Aminoglycosides** (e.g., streptomycin) and some other antibiotics cause **nephrotoxicity** through tubular damage. - Isoniazid is not significantly nephrotoxic and does not require renal dose adjustment.

Question 218: A 25-year-old woman is brought to the emergency department because of a 1-day history of lower abdominal pain and vaginal bleeding. Her last menstrual period was 7 weeks ago. A urine pregnancy test is positive. A pelvic ultrasound shows a normal appearing uterus with an empty intrauterine cavity and a minimal amount of free pelvic fluid. Treatment with a drug is begun. Which of the following is the most likely effect of this drug?

A. Increase in thymidine monophosphate
B. Decrease in guanylate
C. Increase in deoxyuridine monophosphate (Correct Answer)
D. Increase in tetrahydrofolate polyglutamate
E. Decrease in phosphoribosyl pyrophosphate

Explanation: ***Increase in deoxyuridine monophosphate*** - The patient's presentation of lower abdominal pain, vaginal bleeding, a positive pregnancy test, and an empty uterus on ultrasound (with minimal free fluid) strongly suggests an **ectopic pregnancy**. - The drug used for medical management of ectopic pregnancy is typically **methotrexate**, which is a **folate analog** that inhibits **dihydrofolate reductase (DHFR)**, leading to an increase in **deoxyuridine monophosphate (dUMP)**. *Increase in thymidine monophosphate* - Methotrexate ultimately leads to a **decrease** in **thymidine monophosphate (TMP)** synthesis by inhibiting the conversion of dUMP to dTMP. - This inhibition of TMP synthesis interferes with **DNA synthesis** and cell proliferation of rapidly dividing cells, like those in an ectopic pregnancy. *Decrease in guanylate* - Methotrexate does not primarily affect the synthesis of guanylate (GMP). - Guanylate synthesis is part of the **purine biosynthesis pathway**, whereas methotrexate's main action is on the **pyrimidine synthesis pathway** (specifically, thymidylate synthesis). *Increase in tetrahydrofolate polyglutamate* - Methotrexate (a folic acid analog) inhibits dihydrofolate reductase, which reduces **dihydrofolate (DHF)** to **tetrahydrofolate (THF)**. - Therefore, it leads to a **decrease**, not an increase, in the active form of folate, **tetrahydrofolate polyglutamate**. *Decrease in phosphoribosyl pyrophosphate* - **Phosphoribosyl pyrophosphate (PRPP)** is a key precursor for both **purine and pyrimidine synthesis**. - Methotrexate's primary mechanism of action is upstream of PRPP in the metabolic pathways, and it does not directly decrease PRPP levels.

Question 219: A 34-year-old male comes to his family physician with complaints of joint pain that has been present for over 7 weeks. Prior to the onset of his arthritis, he recalls having a gastrointestinal infection which caused mild diarrhea and abdominal cramps. He recovered well and had no issues until his joint pain started. A prescription for naproxen was previously prescribed but he still does not feel well. He has no significant past medical or family history. On physical examination, his blood pressure is 120/78 mm Hg, respirations are 17/min, pulse is 64/min, and temperature is 36.7°C (98.0°F). Which of the following therapies is likely to be most beneficial in treating this patient’s condition?

A. Ketoprofen
B. Ceftriaxone
C. Sulfasalazine (Correct Answer)
D. Methotrexate
E. Diclofenac

Explanation: ***Sulfasalazine*** - This patient presents with symptoms highly suggestive of **reactive arthritis**, characterized by **post-infectious arthritis** (following gastrointestinal infection and inadequate response to NSAIDs like naproxen). - **Sulfasalazine** is an effective **disease-modifying antirheumatic drug (DMARD)** often used in reactive arthritis, particularly when NSAIDs are insufficient. *Ketoprofen* - Ketoprofen is another **NSAID**, similar to the naproxen that the patient has already tried and found ineffective. - While NSAIDs are first-line for symptomatic relief, continuing with another NSAID when the first one failed is unlikely to provide sustained benefit, indicating the need for a **DMARD**. *Ceftriaxone* - Ceftriaxone is an **antibiotic** used to treat active bacterial infections. - Reactive arthritis is a **sterile arthritis** that occurs *after* an infection has resolved, so antibiotics are not indicated and will not treat the joint inflammation. *Methotrexate* - Methotrexate is a potent **DMARD** used for various inflammatory arthritides. - While effective, **sulfasalazine** is generally preferred as an initial DMARD for reactive arthritis, especially in cases where peripheral arthritis predominates, before escalating to more potent agents like methotrexate. *Diclofenac* - Diclofenac is also an **NSAID**, falling into the same class of medication as naproxen and ketoprofen. - As the patient's symptoms persisted despite a trial of naproxen, another NSAID is unlikely to be a more beneficial long-term solution.

Question 220: A 35-year-old man comes to the physician because of a 4-month history of intermittent headaches. They have been getting progressively worse and no longer respond to ibuprofen. He also complains of weight gain and excessive sweating. Physical examination shows prominent supraorbital ridges, prognathism, macroglossia with thick lips, and disproportionately broad hands and feet. There is decreased peripheral vision bilaterally on visual field testing. An MRI of the brain shows a mass in the sella turcica. Genetic analysis of a biopsy specimen from the mass shows cells that overexpress adenylyl cyclase. Which of the following is the most appropriate pharmacotherapy for this condition?

A. Octreotide (Correct Answer)
B. Leuprolide
C. Metyrapone
D. Methimazole
E. Risperidone

Explanation: ***Octreotide*** - This patient presents with **acromegaly**, characterized by progressive headaches, weight gain, excessive sweating, and distinctive physical features such as **prominent supraorbital ridges (frontal bossing)**, **prognathism**, **macroglossia**, and **broad hands and feet**. The visual field defects (**bitemporal hemianopsia** as suggested by decreased peripheral vision) and a mass in the **sella turcica** indicate a **pituitary adenoma**. - **Overexpression of adenylyl cyclase** is consistent with a somatotroph adenoma that secretes **growth hormone (GH)**. **Octreotide** is a **somatostatin analog** that suppresses GH secretion from these tumors, making it the most appropriate pharmacotherapy. *Leuprolide* - **Leuprolide** is a **GnRH agonist** primarily used in conditions like **prostate cancer**, **endometriosis**, and **precocious puberty** by downregulating GnRH receptors, leading to reduced LH and FSH. - It is not indicated for the treatment of **acromegaly**, as it does not directly affect growth hormone secretion. *Metyrapone* - **Metyrapone** is an **inhibitor of 11β-hydroxylase**, an enzyme involved in cortisol synthesis. It is used in the diagnosis and treatment of conditions involving **cortisol excess**, such as **Cushing's syndrome**. - This patient's symptoms are suggestive of **growth hormone excess**, not **cortisol excess**, making metyrapone an inappropriate treatment. *Methimazole* - **Methimazole** is an **antithyroid drug** that inhibits thyroid hormone synthesis and is used to treat **hyperthyroidism**, such as in **Graves' disease**. - The clinical presentation clearly points to **acromegaly** due to a pituitary adenoma, not a thyroid disorder. *Risperidone* - **Risperidone** is an **atypical antipsychotic medication** used primarily to treat conditions like **schizophrenia** and **bipolar disorder**. - It has no role in the direct management of a **growth hormone-secreting pituitary adenoma** or the symptoms of acromegaly.

Question 221: A 32-year-old man presents to the clinic for follow up for treatment of latent tuberculosis. He is a healthcare worker and began isoniazid 3 months ago after a routine PPD yielded a 12-mm induration. He feels otherwise well and attributes this to his vegetarian diet that he has been following for the past 4 years. His past medical history is unremarkable, but his family history is significant for a "liver disease," the specifics of which are unknown. Physical exam shows mildly reduced sensation to pinprick over the distal lower extremities. The abdomen is soft, nontender, and without hepatosplenomegaly. Laboratory studies demonstrate the following: Serum: Hemoglobin: 9.6 g/dL Hematocrit: 34% Leukocyte count: 9,200/mm^3 with normal differential Platelets: 270,000/mm^3 Mean corpuscular volume: 77 µm^3 AST: 92 U/L ALT: 84 U/L Ferritin: 302 ng/mL (normal 15-200 ng/mL) Total iron: 273 µg/dL (normal 50-170 µg/dL) TIBC: 150 µg/dL (normal 250–370 µg/dL) Which of the following is the most appropriate next step in management?

A. Blood lead levels
B. Cobalamin supplementation
C. Stop isoniazid treatment
D. Pyridoxine supplementation (Correct Answer)
E. Serial phlebotomy

Explanation: ***Pyridoxine supplementation*** - This patient is experiencing **peripheral neuropathy** (reduced sensation to pinprick over the distal lower extremities) and **microcytic anemia**, which are common side effects of **isoniazid** due to its interference with **pyridoxine (vitamin B6) metabolism**. - **Pyridoxine supplementation** is the appropriate next step to manage these side effects, as it can alleviate neuropathy and improve anemia without stopping crucial latent TB treatment. *Blood lead levels* - While **lead poisoning** can cause microcytic anemia and neuropathy, the patient's elevated **ferritin** and **total iron**, along with low **TIBC**, are not typical for lead poisoning. - The direct association with **isoniazid treatment** makes pyridoxine deficiency a more likely cause for the observed symptoms. *Stop isoniazid treatment* - Although isoniazid is causing side effects, his **elevated liver enzymes (AST 92, ALT 84)** are less than 5 times the upper limit of normal, and he has no symptoms of **hepatotoxicity** (like jaundice, severe fatigue). - Stopping treatment for latent TB without significant adverse effects would be premature, especially given the availability of effective countermeasures like pyridoxine. *Cobalamin supplementation* - **Cobalamin (vitamin B12) deficiency** typically causes **macrocytic anemia** and neuropathy. - This patient has **microcytic anemia** (MCV 77 µm^3), making cobalamin deficiency an unlikely cause of his symptoms. *Serial phlebotomy* - **Serial phlebotomy** is used to treat **iron overload (hemochromatosis)**, and while this patient has elevated ferritin and total iron, his presentation is primarily driven by **isoniazid side effects**. - Addressing the **pyridoxine deficiency** is the immediate priority for the neuropathy and anemia, and the iron levels may normalize once the underlying issues are managed.

Question 222: A 25-year-old college student is diagnosed with acute myelogenous leukemia after presenting with a 3-week history of fever, malaise, and fatigue. He has a history of type 1 diabetes mellitus, multiple middle ear infections as a child, and infectious mononucleosis in high school. He currently smokes 1 pack of cigarettes per day, drinks a glass of wine per day, and denies any illicit drug use. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 87/min, and respiratory rate 17/min. On physical examination, his pulses are bounding; his complexion is pale, but breath sounds remain clear. A rapidly progressive form of leukemia is identified, and the patient is scheduled to start intravenous chemotherapy. Which of the following treatments should be given to this patient to prevent or decrease the likelihood of developing acute renal failure during treatment?

A. Sulfinpyrazone
B. Indomethacin
C. Probenecid
D. Colchicine
E. Allopurinol (Correct Answer)

Explanation: ***Allopurinol*** - **Allopurinol** inhibits **xanthine oxidase**, preventing the conversion of xanthine and hypoxanthine to uric acid. - This is crucial in **tumor lysis syndrome** (TLS), a common complication of chemotherapy for rapidly proliferating cancers like AML, where massive cell death releases intracellular contents, including **purines**, which are metabolized to uric acid and can cause **acute renal failure**. *Sulfinpyrazone* - **Sulfinpyrazone** is a uricosuric agent, meaning it increases the excretion of uric acid in the urine. - It is generally contraindicated in TLS because the increased uric acid load in the renal tubules can **aggravate crystal formation** and worsen renal damage, rather than prevent it. *Indomethacin* - **Indomethacin** is a non-steroidal anti-inflammatory drug (NSAID) primarily used for pain and inflammation management. - While it can be used to treat the inflammation associated with **gouty arthritis**, it does not prevent the formation of uric acid during TLS and can even cause direct **renal toxicity**, which would be detrimental in a patient at risk of acute renal failure. *Probenecid* - **Probenecid** is another uricosuric agent, similar to sulfinpyrazone, that works by inhibiting the reabsorption of uric acid in the renal tubules. - Like other uricosurics, it is generally **contraindicated in TLS** due to the risk of exacerbating uric acid nephropathy and acute renal failure by increasing uric acid concentrations in the kidneys. *Colchicine* - **Colchicine** is an anti-inflammatory drug mainly used for the treatment of **acute gout attacks** and familial Mediterranean fever. - It does not lower serum uric acid levels and therefore offers no protection against the **hyperuricemia** and potential renal damage associated with tumor lysis syndrome.

Question 223: A 9-year-old boy is brought to the emergency department by his parents after a 2-day history of fever, productive cough, and severe dyspnea. The parents report that the boy had no health problems at birth but developed respiratory problems as an infant that have continued throughout his life, including recurrent pulmonary infections. Vital signs include: temperature of 37.5ºC (99.5ºF), pulse of 105/min, respiratory rate of 34/min, and SpO2 of 87%. Physical examination shows digital clubbing and cyanosis. Chest X-rays show hyperinflation of the lungs and chronic interstitial changes. The boy’s FEV1/FVC ratio is decreased, and his FRC is increased. The resident reviewing his case is studying new gene therapies for this boy’s condition that will reintroduce the gene for which this boy is defective. An important component of this therapy is identifying a vector for the selective introduction of the replacement gene into the human body. Which of the following would be the best vector to provide gene therapy for this boy’s respiratory symptoms?

A. Human immunodeficiency virus-1
B. Adenovirus (Correct Answer)
C. Rabies virus
D. Rhinovirus
E. Coxsackie A virus

Explanation: ***Adenovirus*** - Adenoviruses are the **most suitable vector for respiratory gene therapy** due to their high efficiency in gene delivery to respiratory epithelial cells and their ability to infect both dividing and non-dividing cells. - The clinical presentation (recurrent pulmonary infections, dyspnea, hyperinflation, digital clubbing, and cyanosis) is characteristic of **cystic fibrosis**, which results from a defect in the *CFTR* gene—a prime target for gene therapy via respiratory delivery. - Adenoviral vectors were extensively studied in CF gene therapy trials due to their **excellent tropism for airway epithelium**. *Incorrect: Human immunodeficiency virus-1* - While HIV-1-derived lentiviruses can transduce non-dividing cells and integrate into the host genome, they are **less efficient in delivering genes to respiratory epithelial cells** compared to adenoviruses. - Concerns regarding **potential insertional mutagenesis** and immune responses make them less ideal for respiratory gene therapy. *Incorrect: Rabies virus* - Rabies virus has strong **neurotropism**, meaning it primarily targets the nervous system, making it unsuitable for direct delivery to lung epithelial cells. - Its use would likely lead to **severe neurological side effects** without effectively treating the underlying lung pathology. *Incorrect: Rhinovirus* - Rhinoviruses typically cause **mild, self-limiting infections of the upper respiratory tract** and are not optimized for stable gene transfer to the lower respiratory tract. - They lack the capacity for **long-term gene expression** required for conditions like cystic fibrosis. *Incorrect: Coxsackie A virus* - Coxsackie A viruses are associated with diseases such as **hand, foot, and mouth disease** and cause acute, transient infections. - They are **not efficient gene delivery vectors** for the respiratory system and could cause unwanted inflammatory responses in the lungs.

Question 224: A 45-year-old man is brought to the emergency department 20 minutes after being rescued from a fire in his apartment complex. He thinks he might have briefly lost consciousness while he was trapped in a smoke-filled room before firefighters were able to free him 20 minutes later. He reports headache, dizziness, and occasional cough. He has no difficulty breathing, speaking, or swallowing. He appears mildly uncomfortable and agitated. His temperature is 36.4°C (97.5°F), pulse is 90/min, respirations are 16/min, and blood pressure is 155/68 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 92%. Breath sounds are coarse. The remainder of the examination shows no abnormalities. Arterial blood gas analysis on room air shows : pH 7.30 PCO2 38 mm Hg PO2 70 mm Hg HCO3- 18 mEq/L COHb 2% (N < 3) In addition to oxygen supplementation with a non-rebreather mask, which of the following is the most appropriate next step in management?

A. Administration of methylene blue
B. Administration of intravenous hydroxycobalamin (Correct Answer)
C. Administration of intravenous dimercaprol
D. Administration of N-acetylcysteine
E. Hyperbaric oxygen therapy

Explanation: ***Administration of intravenous hydroxycobalamin*** - This patient presents with symptoms of **smoke inhalation** (headache, dizziness, agitation, exposure to fire) and **metabolic acidosis** (pH 7.30, HCO3- 18 mEq/L) despite normal carboxyhemoglobin (COHb) levels. These findings are highly suggestive of **cyanide poisoning**, which can occur during fires. - **Hydroxocobalamin** is a safe and effective first-line antidote for cyanide poisoning; it binds directly to cyanide to form cyanocobalamin, which is then renally excreted. *Administration of methylene blue* - **Methylene blue** is used to treat **methemoglobinemia**, a condition where iron in hemoglobin is oxidized, reducing oxygen-carrying capacity. - This patient's symptoms and lab findings (normal COHb, metabolic acidosis) are not consistent with methemoglobinemia. *Administration of intravenous dimercaprol* - **Dimercaprol** (BAL) is a chelating agent primarily used for poisoning with **heavy metals** such as arsenic, lead, or mercury. - There is no indication of heavy metal poisoning from the patient's history or clinical presentation. *Administration of N-acetylcysteine* - **N-acetylcysteine (NAC)** is primarily used as an antidote for **acetaminophen overdose** and as a mucolytic. - It is not indicated for cyanide poisoning or the symptoms presented by this patient. *Hyperbaric oxygen therapy* - **Hyperbaric oxygen therapy (HBO)** is the definitive treatment for severe **carbon monoxide poisoning**, as it rapidly decreases the half-life of carboxyhemoglobin. - While carbon monoxide exposure is common in fires, this patient's COHb level is normal (2%), making HBO less appropriate than specific cyanide treatment given the strong suspicion of cyanide poisoning.

Question 225: A 21-year-old man presents to the physician with complaint of fever and non-bloody diarrhea for the past 3 days, after a week of constipation. He and his family recently returned from a summer spent in New Delhi, India visiting relatives. Physical examination reveals abdominal tenderness and a pink macular rash extending from his trunk to his upper arms. His vital signs are as follows: temperature is 99.7°F (37.6°C), blood pressure is 120/72 mmHg, pulse is 85/min, and respirations are 16/min. Which of the following drugs would be most effective in treating this patient’s condition?

A. Oral rehydration solution
B. Penicillin
C. Ciprofloxacin (Correct Answer)
D. Oral vancomycin
E. Metronidazole

Explanation: ***Ciprofloxacin*** - The patient's symptoms (fever, initial constipation followed by diarrhea, abdominal tenderness, **rose spots** or pink macular rash on trunk and upper arms, and recent travel to an endemic area like New Delhi) are highly suggestive of **Typhoid fever** caused by *Salmonella Typhi*. - **Important note**: While ciprofloxacin and other fluoroquinolones were historically first-line agents for typhoid fever, there is now **widespread fluoroquinolone resistance** in South Asia, particularly in India, Pakistan, and Bangladesh. - Among the options listed, ciprofloxacin remains the most appropriate choice, though **azithromycin or ceftriaxone** would be preferred first-line agents in current clinical practice for typhoid acquired in South Asia. - Ciprofloxacin may still have some efficacy and is the best option available from this list. *Oral rehydration solution* - This is a supportive treatment for **dehydration** caused by diarrhea, and while important for symptom management, it does not treat the underlying bacterial infection. - It is crucial for preventing severe dehydration but is not curative for typhoid fever. *Penicillin* - Penicillin is a **beta-lactam antibiotic** that is generally ineffective against *Salmonella Typhi*. - *Salmonella Typhi* are typically resistant to penicillin and other similar narrow-spectrum antibiotics. *Oral vancomycin* - **Oral vancomycin** is primarily used to treat **Clostridioides difficile infection** (CDI) due to its poor systemic absorption. - It has no significant activity against *Salmonella Typhi* and would be ineffective for typhoid fever. *Metronidazole* - Metronidazole is an antibiotic primarily effective against **anaerobic bacteria** and **parasites** (e.g., *Giardia*, *Entamoeba histolytica*).

Question 226: A 59-year-old man comes to the physician because of a painful, burning red rash on his face and hands, which developed 30 minutes after going outside to do garden work. He wore a long-sleeved shirt and was exposed to direct sunlight for about 10 minutes. The patient is light-skinned and has a history of occasional sunburns when he does not apply sunscreen. The patient was diagnosed with small cell lung carcinoma 2 months ago and is currently undergoing chemotherapy. He is currently taking demeclocycline for malignancy-associated hyponatremia and amoxicillin for sinusitis. He has also had occasional back pain. He takes zolpidem and drinks 1–2 glasses of brandy before going to sleep every night. He has smoked a pack of cigarettes daily for 20 years. His pulse is 72/min and his blood pressure is 120/75 mm Hg. Physical examination shows prominent erythema on his forehead, cheeks, and neck. Erythema and papular eruptions are seen on the dorsum of both hands. Which of the following is the most likely cause of this patient's symptoms?

A. Normal sunburn reaction
B. Adverse reaction to amoxicillin
C. Systemic lupus erythematosus
D. Use of demeclocycline (Correct Answer)
E. Uroporphyrin accumulation

Explanation: ***Use of demeclocycline*** - The patient's acute, burning erythematous rash on sun-exposed areas (face, hands) after brief sun exposure is highly suggestive of **photosensitivity**. - **Demeclocycline**, a tetracycline antibiotic, is a known cause of **phototoxic reactions**, making it the most likely culprit given his current medications. *Normal sunburn reaction* - A normal sunburn, while possible with brief exposure in a light-skinned individual, would typically take longer than **30 minutes** to develop a prominent, burning rash. - The severity and rapid onset of symptoms are more indicative of a **phototoxic reaction** rather than a typical sunburn. *Adverse reaction to amoxicillin* - While amoxicillin can cause drug eruptions, they typically manifest as a **morbilliform rash** or **urticaria (hives)**, not a localized, burning rash primarily in sun-exposed areas. - Amoxicillin is **not commonly associated** with photosensitivity. *Systemic lupus erythematosus* - SLE can cause photosensitive rashes (e.g., **malar rash**, discoid lesions), but these tend to be **chronic** or recurrent, and the acute, rapid onset of a burning sensation after brief exposure is less typical. - Other systemic symptoms of SLE, such as **arthralgias, kidney involvement, or serositis**, are not described as the primary complaint. *Uroporphyrin accumulation* - **Porphyrias**, such as **porphyria cutanea tarda**, involve the accumulation of porphyrins (like uroporphyrin) leading to photosensitivity, blistering, and skin fragility. - While it causes photosensitivity, the classic presentation often includes **blisters, hyperpigmentation, increased skin fragility, and hirsutism**, which are not described in this patient's acute presentation of a purely erythematous, burning rash.

Question 227: A 48-year-old woman with a history of osteoarthritis and hypertension presents to the office complaining of persistent abdominal pain for the last 2 months. She describes the pain as 'burning and achy' that is worse when she eats, which has lead to a weight loss of 4.5 kg (10.0 lb). The patient is currently taking lisinopril and atenolol for her blood pressure and ibuprofen as needed for her osteoarthritis. Her temperature is 37.1°C (98.7°F), heart rate is 75/min, and blood pressure is 120/80 mm Hg. An endoscopy is performed and a gastric ulcer is visualized and biopsied. The biopsy reveals H. pylori infection. Which of the following is the most likely predisposing factor to this patient’s diagnosis?

A. Chronic NSAID use (Correct Answer)
B. Longstanding GERD
C. Age and gender
D. Adverse effect of beta-blockers
E. A congenital diverticulum

Explanation: ***Chronic NSAID use*** - The patient's use of **ibuprofen** for osteoarthritis is a significant risk factor for peptic ulcer disease, especially when combined with *H. pylori* infection. NSAIDs inhibit **prostaglandin synthesis**, impairing the stomach's protective mucous layer. - The abdominal pain worsening with food and subsequent weight loss are classic symptoms of a **gastric ulcer**, which is confirmed by endoscopy and *H. pylori* biopsy. *Longstanding GERD* - While GERD can cause upper abdominal pain, it typically manifests as **heartburn** or **regurgitation**, not usually "burning and achy" pain made worse by eating in a way that leads to significant weight loss due to a gastric ulcer. - GERD primarily causes esophageal damage, whereas a gastric ulcer involves the stomach lining; although there can be overlap, it's not the primary predisposing factor for a biopsy-confirmed *H. pylori* gastric ulcer. *Age and gender* - While peptic ulcer disease can occur at any age, the patient's age and gender are not direct predisposing factors for a **gastric ulcer** in the same way that NSAID use or *H. pylori* infection are. - These factors do not explain the specific mechanism of ulcer formation in her case as directly as her medication history. *Adverse effect of beta-blockers* - **Beta-blockers** (like atenolol) are not known to cause peptic ulcers as a common or significant adverse effect. - Their primary cardiovascular effects do not directly impact gastric mucosal integrity. *A congenital diverticulum* - A congenital diverticulum, such as a **Meckel's diverticulum**, is typically found in the small intestine and is more associated with complications like inflammation, bleeding, or obstruction, not gastric ulcers. - This condition is also present from birth and not related to the patient's current medications or *H. pylori* infection.

Question 228: A 64-year-old woman presents to the emergency room with complaints of severe, whole-body itching. She states that she first noticed her symptoms while in the bathtub at home. She has never had symptoms like this before. However, over the previous several months she has had episodes of severe joint swelling and pain in her hands as well as redness, burning pain, and swelling of her hands and feet. Her past medical history is significant for type II diabetes mellitus, hypertension, and osteoporosis for which she takes metformin, enalapril, and alendronate, respectively. In addition, she was found to have a deep vein thrombosis of her left leg three months prior to presentation. The patient’s temperature is 98.6°F (37.0°C), pulse is 80/min, blood pressure is 135/85 mmHg, and respirations are 13/min. Physical exam is notable for a woman in discomfort with excoriations over the skin on her forearms. The patient’s laboratory tests are shown below. Serum: Na+: 135 mEq/L Cl-: 100 mEq/L K+: 5.0 mEq/L HCO3-: 22 mEq/L BUN: 19 mg/dL Glucose: 130 mg/dL Creatinine: 1.0 mg/dL Hematocrit: 64% Leukocyte count: 19,000 cells/mm^3 with normal differential Platelet count: 900,000/mm^3 What is the best next step in treatment of this patient's underlying condition?

A. Febuxostat
B. Hydroxyurea (Correct Answer)
C. Prednisone
D. Cyclophosphamide
E. Diphenhydramine

Explanation: ***Hydroxyurea*** * The patient's clinical picture, including whole-body itching, severe joint pain and swelling (gout), redness and burning pain in hands and feet (**erythromelalgia**), a history of DVT, elevated hematocrit (**64%**), very high leukocyte count (**19,000/mm³**) with normal differential, and extremely elevated platelet count (**900,000/mm³**), strongly suggests **polycythemia vera**. * **Hydroxyurea** is a first-line cytoreductive agent used to control myelosuppression and reduce the risk of thrombotic events in high-risk patients with polycythemia vera. *Febuxostat* * **Febuxostat** is a **xanthine oxidase inhibitor** used to treat **gout** by lowering uric acid levels. While the patient has symptoms suggestive of gout, this addresses only one complication and not the underlying myeloproliferative disorder. * It would not address the thrombotic risk associated with polycythemia vera or control the high blood counts. *Prednisone* * **Prednisone** is a corticosteroid used to treat inflammatory and autoimmune conditions. * While it might temporarily alleviate symptoms like pain or itching, it is not a definitive treatment for a myeloproliferative neoplasm like polycythemia vera and could worsen glucose control. *Cyclophosphamide* * **Cyclophosphamide** is an **alkylating agent** used primarily in chemotherapy for various cancers and autoimmune diseases. * It is generally reserved for more aggressive conditions or in cases when hydroxyurea or other first-line agents are ineffective or contraindicated. It is not the initial best step for polycythemia vera. *Diphenhydramine* * **Diphenhydramine** is an **antihistamine** used to relieve itching. * While it could acutely help with the pruritus, it only addresses a symptom and does not treat the underlying cause of the severe itching, which is related to the myeloproliferative disorder.

Question 229: A 32-year-old man presents with a 1-week history of progressive diplopia followed by numbness and tingling in his hands and feet, some weakness in his extremities, and occasional difficulty swallowing. He was recently diagnosed with Hodgkin's lymphoma and started on a chemotherapeutic regimen that included bleomycin, doxorubicin, cyclophosphamide, vincristine, and prednisone. He denies fever, recent viral illness, or vaccination. On neurological examination, he has bilateral ptosis. His bilateral pupils are 5 mm in diameter and poorly responsive to light and accommodation. He has a bilateral facial weakness and his gag reflex is reduced. Motor examination using the Medical Research Council scale reveals a muscle strength of 4/5 in the proximal muscles of upper extremities bilaterally and 2/5 in distal muscles. In his lower extremities, hip muscles are mildly weak bilaterally, and he has bilateral foot drop. Deep tendon reflexes are absent. Sensory examination reveals a stocking-pattern loss to all sensory modalities in the lower extremities up to the middle of his shins. A brain MRI is normal. Lumbar puncture is unremarkable. His condition can be explained by a common adverse effect of which of the following drugs?

A. Doxorubicin
B. Bleomycin
C. Cyclophosphamide
D. Prednisone
E. Vincristine (Correct Answer)

Explanation: ***Vincristine*** - The patient's symptoms of **progressive diplopia**, **numbness and tingling**, **weakness (especially distal foot drop)**, **cranial nerve palsies (ptosis, facial weakness, reduced gag reflex)**, and **absent deep tendon reflexes (areflexia)**, along with a **stocking-glove sensory loss**, are highly indicative of **vincristine-induced peripheral neuropathy**. - **Vincristine** is a vinca alkaloid commonly used in Hodgkin's lymphoma treatment known for its **neurotoxicity**, primarily affecting **sensory and motor peripheral nerves** and **cranial nerves**. *Doxorubicin* - **Doxorubicin** is an anthracycline known for its **cardiotoxicity**, which can lead to **dilated cardiomyopathy** and **congestive heart failure**. - It does not typically cause the prominent **peripheral neuropathy** and **cranial nerve deficits** observed in this patient. *Bleomycin* - **Bleomycin** is an antitumor antibiotic primarily associated with **pulmonary toxicity**, including **fibrosis and pneumonitis**. - It does not cause significant **neurological side effects** like polyneuropathy. *Cyclophosphamide* - **Cyclophosphamide** is an alkylating agent known for its side effects such as **hemorrhagic cystitis**, **bone marrow suppression**, and **gonadal dysfunction**. - It generally does not cause **peripheral neuropathy** or **cranial nerve palsies** as its primary toxicity. *Prednisone* - **Prednisone** is a corticosteroid that can cause a wide range of side effects including **hyperglycemia**, **immunosuppression**, **osteoporosis**, and **myopathy (proximal weakness)** with prolonged use. - While it can cause some muscle weakness, it does not typically present with the **distal nerve involvement**, **sensory loss**, **diplopia**, and **areflexia** seen in this patient.

Question 230: A 26-year-old student arrives to student health for persistent diarrhea. She states that for the past 2 months she has had foul-smelling diarrhea and abdominal cramping. She also reports increased bloating, flatulence, and an unintentional 4 lb weight loss. Prior to 2 months ago, she had never felt these symptoms before. She denies other extra-gastrointestinal symptoms. The patient is an avid hiker and says her symptoms have caused her to miss recent camping trips. The patient has tried to add more fiber to her diet without relief. She feels her symptoms worsen with milk or cheese. Her medical history is insignificant and she takes no medications. She drinks whiskey socially, but denies smoking tobacco or using any illicit drugs. She is sexually active with her boyfriend of 2 years. She went to Mexico 6 months ago and her last multi-day backpacking trek was about 3 months ago in Vermont. Physical examination is unremarkable. A stool sample is negative for fecal occult blood. Which of the following is an associated adverse effect of the most likely treatment given to manage the patient’s symptoms?

A. Tendon rupture
B. QT prolongation
C. Photosensitivity
D. Disulfiram-like reaction (Correct Answer)
E. Osteoporosis

Explanation: ***Disulfiram-like reaction*** - The patient's symptoms (foul-smelling diarrhea, bloating, flatulence, weight loss after hiking) are highly suggestive of **Giardiasis**, which is commonly treated with **metronidazole**. - **Metronidazole** is known to cause a **disulfiram-like reaction** when consumed with alcohol, as it inhibits aldehyde dehydrogenase, leading to an accumulation of acetaldehyde. *Tendon rupture* - **Tendon rupture** is a well-known adverse effect associated with **fluoroquinolone antibiotics** (e.g., ciprofloxacin, levofloxacin). - Fluoroquinolones are not the first-line treatment for Giardiasis, and there is no indication for their use in this patient's presentation. *QT prolongation* - **QT prolongation** is a potential adverse effect of several medications, including some **macrolide antibiotics** (e.g., azithromycin), certain **antifungals**, and **antiarrhythmics**. - While some medications used for parasitic infections might rarely cause this, it's not a primary or common side effect of metronidazole. *Photosensitivity* - **Photosensitivity** reactions are commonly associated with certain **antibiotics** (e.g., tetracyclines, sulfonamides), **diuretics**, and **NSAIDs**. - This adverse effect is not typically linked to metronidazole. *Osteoporosis* - **Osteoporosis** is a long-term skeletal condition often linked to chronic corticosteroid use, hormonal imbalances, or certain chronic diseases. - It is not an acute or common adverse effect of anti-parasitic medications like metronidazole.

Question 231: A 29-year-old man presents to the primary care clinic in June for post-discharge follow-up. The patient was recently admitted to the hospital after a motor vehicle collision. At that time he arrived at the emergency department unconscious, hypotensive, and tachycardic. Abdominal CT revealed a hemoperitoneum due to a large splenic laceration; he was taken to the operating room for emergency splenectomy. Since that time he has recovered well without complications. Prior to the accident, he was up-to-date on all of his vaccinations. Which of the following vaccinations should be administered at this time?

A. Inactivated (intramuscular) influenza vaccine
B. Live attenuated (intranasal) influenza vaccine
C. Tetanus booster vaccine
D. Measles-mumps-rubella vaccine
E. 13-valent pneumococcal conjugate vaccine (Correct Answer)

Explanation: ***13-valent pneumococcal conjugate vaccine*** - Patients who have undergone a **splenectomy** are at increased risk for **overwhelming post-splenectomy infection (OPSI)**, particularly from encapsulated bacteria like *Streptococcus pneumoniae*. - The **13-valent pneumococcal conjugate vaccine (PCV13)** and the **23-valent pneumococcal polysaccharide vaccine (PPSV23)** are crucial for protection, with PCV13 typically given first. *Inactivated (intramuscular) influenza vaccine* - While recommended annually for most individuals, especially those with chronic conditions, influenza vaccination is generally given in the **fall** (September-October) to cover the typical flu season. - Administering it in June is **premature** and not the most urgent vaccination for this patient in a post-splenectomy state. *Live attenuated (intranasal) influenza vaccine* - This vaccine is also administered annually in the fall for seasonal influenza and is **contraindicated** in immunocompromised individuals. - Patients who have undergone splenectomy are considered **immunocompromised**, making this vaccine unsuitable. *Tetanus booster vaccine* - This patient would have likely received a **tetanus vaccine** at the time of the motor vehicle collision if their vaccination status was unknown or incomplete, as it's indicated for traumatic wounds. - There is no indication for an additional tetanus booster based on his current presentation or recent hospital stay. *Measles-mumps-rubella vaccine* - The patient was noted to be **up-to-date on all vaccinations** prior to the accident, implying he has likely already received the MMR vaccine. - There is no specific indication for an additional MMR vaccine due to splenectomy, unlike for encapsulated bacteria.

Question 232: A 55-year-old woman presents with diarrhea and a rash. She reports having some painful reddish nodules on her legs that she noticed a week ago. She also has been having loose stools associated with cramping lower abdominal pain for the past month. This is associated with an urgency to defecate, and defecation helps relieve the abdominal pain. The stool is occasionally blood-tinged and has some mucus. She feels fatigued but denies fever, weight loss, exposure to any sick people, or history of travel recently. No significant past medical history. Her family history is significant for osteoporosis in her mother, aunt, and older sister. On physical examination, the patient has generalized pallor. There are multiple erythematous tender nodules over the extensor surface of the legs bilaterally below the level of the knee. Abdominal examination reveals mild tenderness to palpation in the left lower quadrant. A DEXA scan is performed and reveals a T-score of -1.5 at the hips and spine. Laboratory findings are significant for microcytic anemia and an elevated ESR. A colonoscopy is performed and reveals patchy inflammation of the colon with rectal sparing. The lesions are present in patches with intermittent normal colonic mucosa. The patient is started on sulfasalazine and shows a good response. However, 6 months later, she returns with a recurrence of her symptoms. A repeat colonoscopy reveals more extensive involvement of the colon and the small bowel. A second drug is added to her treatment regimen. Which of the following is the most common adverse effect associated with the use of this second drug?

A. Hepatotoxicity
B. Infection (Correct Answer)
C. Megaloblastic anemia
D. Worsening of osteoporosis
E. Rash

Explanation: ***Infection*** - The patient's presentation with **patchy inflammation** of the colon, rectal sparing, and later small bowel involvement, along with **erythema nodosum** and **microcytic anemia**, is highly suggestive of **Crohn's disease**. - Given the recurrence and more extensive involvement, it's likely a **biologic agent** (e.g., TNF-alpha inhibitor) or an **immunomodulator** (e.g., methotrexate, azathioprine) was added. These drugs **suppress the immune system**, making **infection** the most common and serious adverse effect. *Hepatotoxicity* - While some drugs used in Crohn's disease, such as **methotrexate** or **azathioprine**, can cause hepatotoxicity, it is generally monitored and is less common than infection. - **Biologics**, which are frequently used for refractory Crohn's, pose a lower risk of hepatotoxicity compared to their immunomodulatory effects. *Megaloblastic anemia* - **Megaloblastic anemia** is typically associated with **folate deficiency** (which can be caused by sulfasalazine or methotrexate) or **B12 deficiency** (which can occur in Crohn's affecting the terminal ileum). - While possible, it is not the most common adverse effect of the second-line agents used to treat Crohn's disease. *Worsening of osteoporosis* - **Osteoporosis** is a common comorbidity in Crohn's disease due to chronic inflammation, malabsorption, and corticosteroid use, but it is not a direct adverse effect of most second-line medications. - While **corticosteroids** can worsen osteoporosis, they are typically used for acute flares, and the newer biologic or immunomodulatory agents do not directly cause bone loss. *Rash* - **Rash** can be an adverse effect of many medications, including some used for Crohn's disease like **sulfasalazine** or **biologics**. - However, **infection** due to immunosuppression is a far more pervasive and common risk across a broader range of the second-line therapies used in Crohn's disease management.

Question 233: A laboratory physician investigates the chromosomes of a fetus with a suspected chromosomal anomaly. She processes a cell culture obtained by amniocentesis. Prior to staining and microscopic examination of the fetal chromosomes, a drug that blocks cell division is added to the cell culture. In order to arrest chromosomes in metaphase, the physician most likely added a drug that is also used for the treatment of which of the following conditions?

A. Trichomonas vaginitis
B. Testicular cancer
C. Herpes zoster
D. Polycythemia vera
E. Acute gouty arthritis (Correct Answer)

Explanation: ***Acute gouty arthritis*** - The drug used to arrest chromosomes in metaphase is likely **colchicine**, which inhibits **microtubule polymerization** and spindle formation, thus arresting cells in metaphase. - **Colchicine** is a well-established treatment for **acute gouty arthritis** due to its anti-inflammatory properties, primarily through disrupting neutrophil functions. *Trichomonas vaginitis* - This condition is typically treated with **metronidazole** or **tinidazole**, which are antibiotics targeting protozoa and anaerobic bacteria. - These drugs do not inhibit microtubule assembly or arrest cells in metaphase. *Testicular cancer* - Testicular cancer is primarily treated with **BEP regimen** (bleomycin, etoposide, cisplatin), which does not include microtubule-inhibiting agents. - While vinca alkaloids (vincristine, vinblastine) do arrest cells in metaphase via microtubule inhibition similar to colchicine, they are not standard first-line agents for testicular cancer. - The question specifically asks about the primary clinical use of colchicine, which is gout, not cancer chemotherapy. *Herpes zoster* - Herpes zoster (shingles) is a viral infection treated with **antiviral medications** like acyclovir, valacyclovir, or famciclovir. - These antivirals work by interfering with viral DNA replication and do not target microtubule formation or cell division. *Polycythemia vera* - Polycythemia vera is a myeloproliferative neoplasm often managed with **phlebotomy**, **hydroxyurea**, or ruxolitinib. - These treatments aim to reduce blood cell counts or inhibit specific signaling pathways, none of which primarily involve arresting cells in metaphase by disrupting microtubules.

Question 234: A 30-year-old man comes to the emergency department because of the sudden onset of back pain beginning 2 hours ago. Beginning yesterday, he noticed that his eyes started appearing yellowish and his urine was darker than normal. Two months ago, he returned from a trip to Greece, where he lived before immigrating to the US 10 years ago. Three days ago, he was diagnosed with latent tuberculosis and started on isoniazid. He has worked as a plumber the last 5 years. His temperature is 37.4°C (99.3°F), pulse is 80/min, and blood pressure is 110/70 mm Hg. Examination shows back tenderness and scleral icterus. Laboratory studies show: Hematocrit 29% Leukocyte count 8000/mm3 Platelet count 280,000/mm3 Serum Bilirubin Total 4 mg/dL Direct 0.7 mg/dL Haptoglobin 15 mg/dL (N=41–165 mg/dL) Lactate dehydrogenase 180 U/L Urine Blood 3+ Protein 1+ RBC 2–3/hpf WBC 2–3/hpf Which of the following is the most likely underlying cause of this patient's anemia?

A. Absence of reduced glutathione (Correct Answer)
B. Absence of uridine 5'-monophosphate
C. Crescent-shaped erythrocytes
D. Defective ankyrin in the RBC membrane
E. Inhibition of aminolevulinate dehydratase

Explanation: ***Absence of reduced glutathione*** - This patient's presentation with anemia, jaundice, dark urine, and particularly the low **haptoglobin** and elevated **LDH**, points to **hemolysis**. The recent initiation of **isoniazid** (an oxidative stressor) and his Greek ancestry strongly suggest **G6PD deficiency**, where a lack of reduced glutathione leads to oxidative damage and hemolysis. - **Glucose-6-phosphate dehydrogenase (G6PD) deficiency** is an X-linked recessive disorder common in populations of Mediterranean and African descent. It impairs the **hexose monophosphate shunt**, reducing the cell's ability to produce **NADPH**, which is crucial for reducing **oxidative stress** via **reduced glutathione**. *Absence of uridine 5'-monophosphate* - Absence of **uridine 5'-monophosphate (UMP)** is associated with **hereditary orotic aciduria**, a rare metabolic disorder. - This condition typically presents with **megaloblastic anemia** (not hemolytic anemia), growth retardation, and orotic acid crystals in the urine, none of which are consistent with this patient's findings. *Crescent-shaped erythrocytes* - **Crescent-shaped erythrocytes** (sickle cells) are characteristic of **sickle cell anemia**, a genetic disorder causing chronic hemolytic anemia, vaso-occlusive crises, and pain. - While it can cause hemolytic anemia, the triggers and specific laboratory findings (e.g., absence of a specific oxidative stressor like isoniazid causing acute hemolysis, the sudden onset in an adult not previously diagnosed) make it less likely than G6PD deficiency in this context. *Defective ankyrin in the RBC membrane* - Defective **ankyrin** in the red blood cell membrane is characteristic of **hereditary spherocytosis**, an inherited disorder causing hemolytic anemia. - This condition typically presents with **spherocytes** on the blood smear, increased **MCHC**, and a positive **osmotic fragility test**, which are not indicated by the provided lab results. *Inhibition of aminolevulinate dehydratase* - Inhibition of **aminolevulinate dehydratase** is associated with **lead poisoning**, which impairs **heme synthesis**. - This would typically cause a **microcytic or normocytic anemia** with **basophilic stippling** and elevated **protoporphyrin levels**, not an acute hemolytic crisis with jaundice, low haptoglobin, and elevated LDH.

Question 235: A 45-year-old female with a history of gastroesophageal reflux disease presents to her family physician with symptoms of epigastric pain right after a meal. The physician performs a urea breath test which is positive and the patient is started on appropriate medical therapy. Three days later at a restaurant, she experienced severe flushing, tachycardia, hypotension, and vomiting after her first glass of wine. Which of the following is the mechanism of action of the medication causing this side effect?

A. Binds to the 30S ribosomal subunit preventing attachment of the aminoacyl-tRNA
B. Blocks protein synthesis by binding to the 50S ribosomal subunit inhibiting protein translocation
C. Blocks the synthesis of the peptidoglycan layer
D. Inhibits the H+/K+ ATPase
E. Forms toxic metabolites that damage bacterial DNA (Correct Answer)

Explanation: ***Forms toxic metabolites that damage bacterial DNA*** - The patient likely has a **_H. pylori_ infection** causing epigastric pain, diagnosed by a **positive urea breath test**. - **Metronidazole**, a common treatment for _H. pylori_, causes a **disulfiram-like reaction** with alcohol, leading to flushing, tachycardia, hypotension, and vomiting. Metronidazole's mechanism involves forming **toxic free radicals** that damage bacterial DNA. *Binds to the 30S ribosomal subunit preventing attachment of the aminoacyl-tRNA* - This is the mechanism of action for **tetracyclines** (e.g., doxycycline) and **aminoglycosides** (e.g., gentamicin), which are sometimes used in _H. pylori_ regimens but do not typically cause this severe alcohol interaction. - While tetracyclines are part of some _H. pylori_ treatment regimens, they are not primarily associated with a disulfiram-like reaction. *Blocks protein synthesis by binding to the 50S ribosomal subunit inhibiting protein translocation* - This describes the mechanism of action of **macrolide antibiotics** (e.g., clarithromycin), which are commonly used in _H. pylori_ treatment protocols. - Although clarithromycin can cause gastrointestinal upset, it does not typically induce the severe disulfiram-like reaction described with alcohol. *Blocks the synthesis of the peptidoglycan layer* - This is the mechanism of action of **beta-lactam antibiotics** (e.g., amoxicillin), frequently included in _H. pylori_ eradication regimens. - Amoxicillin does not cause a disulfiram-like reaction when combined with alcohol. *Inhibits the H+/K+ ATPase* - This describes **proton pump inhibitors (PPIs)** like omeprazole or pantoprazole, which are part of nearly all _H. pylori_ treatment regimens to reduce acid production. - PPIs do not have a direct interaction with alcohol that causes this specific constellation of symptoms; their primary role is acid suppression, not antibacterial action leading to disulfiram effects.

Question 236: A 14-year-old girl is brought to the physician after she accidentally cut her right forearm earlier that morning while working with her mother's embroidery scissors. She has no history of serious illness. The mother says she went to elementary and middle school abroad and is not sure if she received all of her childhood vaccinations. She appears healthy. Her temperature is 37°C (98.6 °F), pulse 90/min, and blood pressure is 102/68 mm Hg. Examination shows a clean 2-cm laceration on her right forearm with surrounding edema. There is no erythema or discharge. The wound is irrigated with water and washed with soap. Which of the following is the most appropriate next step in management?

A. Administer Tdap only (Correct Answer)
B. Administer DTaP only
C. No further steps are necessary
D. Administer TIG only
E. Intravenous metronidazole

Explanation: ***Administer Tdap only*** - A 14-year-old with an unknown or incomplete vaccination history requires a **Tdap (tetanus, diphtheria, acellular pertussis) booster** for **tetanus prophylaxis** after a wound. - The wound is clean, and there are no signs of active infection or high-risk features that would necessitate tetanus immune globulin (TIG). *Administer DTaP only* - **DTaP (diphtheria, tetanus, acellular pertussis)** is typically administered to children younger than 7 years of age. - This patient is 14 years old, making Tdap the more appropriate vaccine formulation for her age group. *No further steps are necessary* - Given the patient's **unknown vaccination history** and a laceration, tetanus prophylaxis is crucial to prevent **tetanus**, a potentially life-threatening condition. - Simply cleaning the wound is insufficient protection without adequate vaccination status. *Administer TIG only* - **Tetanus immune globulin (TIG)** is typically reserved for patients with **dirty or severe wounds** and an unknown or incomplete vaccination history, or for those who are immunocompromised. - This patient has a **clean laceration** with no indication of high-risk features that would warrant TIG. *Intravenous metronidazole* - **Metronidazole** is an antibiotic used to treat **anaerobic bacterial infections** and certain parasitic infections. - The patient has no signs of infection (no erythema, discharge, or fever) that would necessitate antibiotic treatment at this time.

Question 237: A 24-year-old woman of Ashkenazi Jewish descent presents with recurrent bloody diarrhea and abdominal pain. She says she feels well otherwise. Review of systems is significant for a 4 kg weight loss over the past month. Physical examination is significant for multiple aphthous oral ulcers. Colonoscopy reveals a cobblestone pattern of lesions of the mucosa of the intestinal wall with skip lesions involving the terminal ileum and colon. The patient is informed of the diagnosis and medication to treat her condition is prescribed. On a follow-up visit 6 weeks later, the patient presents with non-productive cough, chest pain, dyspnea on exertion, and worsening oral lesions. A chest radiograph reveals a diffuse interstitial pattern. Which of the following enzymes is inhibited by the medication most likely prescribed for her initial diagnosis?

A. Thymidine kinase
B. DNA polymerase
C. Dihydrofolate reductase (Correct Answer)
D. Hypoxanthine guanine-phosphoribosyltransferase (HGPRT)
E. Thymidylate synthase

Explanation: ***Dihydrofolate reductase*** - The patient's initial symptoms (recurrent **bloody diarrhea**, **abdominal pain**, **weight loss**, **oral ulcers**, **cobblestone pattern** of lesions in the sigmoid colon) are highly suggestive of **Crohn's disease**. The patient's **Ashkenazi Jewish descent** is also a risk factor for Crohn's disease. - The worsening oral lesions, cough, chest pain, and **diffuse interstitial pattern** on chest radiograph 6 weeks later are classic signs of **methotrexate toxicity**. Methotrexate, a common treatment for Crohn's disease, inhibits **dihydrofolate reductase**, an enzyme essential for **folate metabolism** and **DNA synthesis**. *Thymidine kinase* - **Thymidine kinase** is an enzyme involved in the salvage pathway of pyrimidine synthesis. It is typically inhibited by antiviral drugs like **acyclovir** and **ganciclovir**, which are not used for Crohn's disease. - Inhibition of thymidine kinase is not associated with the lung and oral toxicities seen in this patient. *DNA polymerase* - **DNA polymerase** is crucial for DNA replication and repair. Drugs inhibiting DNA polymerase, such as some **antivirals** (e.g., foscarnet) and **chemotherapeutics** (e.g., cytarabine), are not primary treatments for Crohn's disease. - Inhibition of DNA polymerase does not directly lead to the specific constellation of symptoms observed from methotrexate toxicity. *Hypoxanthine guanine-phosphoribosyltransferase (HGPRT)* - **HGPRT** is an enzyme central to the purine salvage pathway. Its deficiency leads to **Lesch-Nyhan syndrome**. - While some immunosuppressants like **azathioprine** and **mercaptopurine** act as purine analogs and affect purine metabolism, they do not directly inhibit HGPRT and do not typically cause the acute pulmonary toxicity seen with methotrexate. *Thymidylate synthase* - **Thymidylate synthase** is an enzyme involved in the synthesis of pyrimidine deoxyribonucleotides, particularly dTMP, which is essential for DNA synthesis. It is a target for some **chemotherapeutic agents** like **5-fluorouracil**. - While methotrexate indirectly affects thymidylate synthesis by depleting folate precursors, its direct mechanism of action is the inhibition of **dihydrofolate reductase**, not thymidylate synthase itself, and 5-fluorouracil toxicity differs from the presented symptoms.

Question 238: A 17-year-old male is diagnosed with acne vulgaris during a visit to a dermatologist. He is prescribed a therapy that is a derivative of vitamin A. He has no other significant past medical history. Which of the following is a major side-effect of this therapy that requires regular monitoring during treatment?

A. Alopecia
B. Hyperglycemia
C. Fatigue
D. Hyperlipidemia (Correct Answer)
E. Xerophthalmia

Explanation: ***Hyperlipidemia*** - **Isotretinoin**, a vitamin A derivative, is known to cause significant alterations in lipid metabolism, necessitating regular monitoring of **triglycerides** and **cholesterol** levels. - Elevated lipid levels, particularly triglycerides, can lead to serious complications such as **pancreatitis** if not controlled. *Alopecia* - While hair thinning can occur with isotretinoin, it is not considered a **major side effect** that routinely requires the same level of close periodic monitoring as hyperlipidemia. - Hair changes are generally less common and often reversible upon discontinuation of the drug. *Hyperglycemia* - Although there have been rare reports of altered glucose metabolism, **hyperglycemia** is not a common or major side effect of isotretinoin that mandates routine and frequent monitoring in most patients. - The direct link and clinical significance are not as robust as for lipid abnormalities. *Fatigue* - Fatigue can be a general, non-specific side effect of many medications, including isotretinoin, but it is not typically a serious concern requiring regular laboratory monitoring. - It is often managed symptomatically and does not carry the same risk of organ damage as unmonitored hyperlipidemia. *Xerophthalmia* - **Dry eyes (xerophthalmia)** are a common and expected side effect of isotretinoin due to its systemic drying effects. - While it can be uncomfortable, it is typically managed with artificial tears and does not require regular laboratory monitoring or pose the same severe systemic risks as hyperlipidemia.

Question 239: A 7-year-old boy is brought to the emergency department because of sudden-onset abdominal pain that began 1 hour ago. Three days ago, he was diagnosed with a urinary tract infection and was treated with nitrofurantoin. There is no personal history of serious illness. His parents emigrated from Kenya before he was born. Examination shows diffuse abdominal tenderness, mild splenomegaly, and scleral icterus. Laboratory studies show: Hemoglobin 9.8 g/dL Mean corpuscular volume 88 μm3 Reticulocyte count 3.1% Serum Bilirubin Total 3.8 mg/dL Direct 0.6 mg/dL Haptoglobin 16 mg/dL (N=41–165 mg/dL) Lactate dehydrogenase 179 U/L Which of the following is the most likely underlying cause of this patient's symptoms?

A. Defective red blood cell membrane proteins
B. Lead poisoning
C. Defect in orotic acid metabolism
D. Absent hemoglobin beta chain
E. Enzyme deficiency in red blood cells (Correct Answer)

Explanation: ***Enzyme deficiency in red blood cells*** - The patient's symptoms (abdominal pain, scleral icterus, mild splenomegaly, anemia, elevated reticulocyte count, increased unconjugated bilirubin, low haptoglobin, and elevated LDH) are consistent with **hemolytic anemia**. The recent use of **nitrofurantoin**, an oxidative stressor, in a patient of African descent, strongly suggests a diagnosis of **Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency**. - G6PD deficiency is an **X-linked recessive** inherited enzyme defect causing red blood cells to be susceptible to oxidative damage, leading to hemolysis when exposed to certain drugs (like nitrofurantoin) or infections. *Defective red blood cell membrane proteins* - This describes conditions like **hereditary spherocytosis** or **hereditary elliptocytosis**. While these cause hemolytic anemia, the acute onset triggered by a drug (nitrofurantoin) is less typical. - Hereditary spherocytosis is characterized by **microspherocytes** on a peripheral smear and is usually diagnosed earlier in life or has a chronic course, often without an acute precipitating drug. *Lead poisoning* - Lead poisoning typically causes **microcytic anemia** with **basophilic stippling** and neurological symptoms, not the type of hemolytic anemia and jaundice described. - It does not present as an acute hemolytic crisis triggered by an oxidative drug. *Defect in orotic acid metabolism* - This can lead to conditions like **hereditary orotic aciduria**, which presents with **megaloblastic anemia** (without B12 or folate deficiency) and developmental delay. - It is not associated with acute hemolytic episodes triggered by oxidative drugs or the specific lab findings seen here. *Absent hemoglobin beta chain* - This refers to **beta-thalassemia major**, which causes **microcytic hypochromic anemia** that is typically chronic and presents early in childhood with severe anemia requiring regular transfusions. - Beta-thalassemia does not present as an acute hemolytic crisis triggered by nitrofurantoin, and the MCV in this patient is normal (88 μm³), not microcytic.

Question 240: A 25-year-old man presents to the emergency department with bilateral eye pain. The patient states it has slowly been worsening over the past 48 hours. He admits to going out this past weekend and drinking large amounts of alcohol and having unprotected sex but cannot recall a predisposing event. The patient's vitals are within normal limits. Physical exam is notable for bilateral painful and red eyes with opacification and ulceration of each cornea. The patient's contact lenses are removed and a slit lamp exam is performed and shows bilateral corneal ulceration. Which of the following is the best treatment for this patient?

A. Topical dexamethasone and refrain from wearing contacts
B. Intravitreal vancomycin and ceftazidime
C. Gatifloxacin eye drops (Correct Answer)
D. Erythromycin ointment
E. Acyclovir

Explanation: ***Gatifloxacin eye drops*** - The patient's presentation with **bilateral painful red eyes**, **corneal opacification and ulceration**, and a history of **contact lens use** strongly suggests **bacterial keratitis**. - **Gatifloxacin** is a **fourth-generation fluoroquinolone** that provides broad-spectrum coverage against common bacterial pathogens causing keratitis, including gram-positive and gram-negative organisms, and is administered as a topical eye drop. *Topical dexamethasone and refrain from wearing contacts* - While refraining from contact lens use is crucial, **topical corticosteroids** like dexamethasone are generally **contraindicated in active bacterial keratitis** as they can worsen the infection by suppressing the immune response. - Corticosteroids are primarily used in inflammatory conditions, and their use in suspected infections can delay healing and promote microbial growth. *Intravitreal vancomycin and ceftazidime* - This treatment regimen is typically reserved for severe **endophthalmitis**, an intraocular infection, not for keratitis which is an infection of the cornea. - **Intravitreal injections** are significantly more invasive and carry higher risks than topical treatments for corneal infections. *Erythromycin ointment* - **Erythromycin ointment** is a macrolide antibiotic with a **narrower spectrum of activity** compared to fluoroquinolones, particularly against some gram-negative bacteria common in contact lens-related keratitis. - While it can be used for some superficial ocular infections, it is likely **insufficient for severe keratitis** presenting with significant ulceration. *Acyclovir* - **Acyclovir** is an **antiviral medication** used to treat **herpes simplex keratitis** or **herpes zoster ophthalmicus**. - While corneal ulcers can be caused by viruses, the clinical picture, especially the **contact lens use** and rapid progression, points more strongly towards **bacterial keratitis**.

Question 241: A 35-year-old woman that has recently immigrated from Southeast Asia is brought to the emergency department due to a 3-week history of fatigue, night sweats, and enlarged lymph nodes and persistent fever. These symptoms have been getting worse during the past week. She has no history of any cardiac or pulmonary disease. A chest X-ray reveals ipsilateral hilar enlargement and a rounded calcified focus near the right hilum. A Mantoux test is positive. Sputum samples are analyzed and acid-fast bacilli are identified on Ziehl-Neelsen staining. The patient is started on a 4 drug regimen. She returns after 6 months to the emergency department with complaints of joint pain, a skin rash that gets worse with sunlight and malaise. The antinuclear antibody (ANA) and anti-histone antibodies are positive. Which of the following drugs prescribed to this patient is the cause of her symptoms?

A. Isoniazid (Correct Answer)
B. Pyrazinamide
C. Ethambutol
D. Streptomycin
E. Rifampicin

Explanation: ***Isoniazid*** - The patient developed symptoms of **drug-induced lupus erythematosus (DILE)**, characterized by joint pain, photosensitive rash, and positive ANA and anti-histone antibodies, which is a known side effect of isoniazid. - Isoniazid is a common cause of DILE because it is metabolized to a compound that can induce autoantibody production, particularly **anti-histone antibodies**. *Pyrazinamide* - Pyrazinamide is primarily associated with **hepatotoxicity** and **hyperuricemia**, which can lead to Gout. - It does not commonly cause drug-induced lupus erythematosus. *Ethambutol* - **Optic neuritis** (blurred vision, red-green color blindness) is the most significant side effect of ethambutol. - It is not associated with drug-induced lupus erythematosus. *Streptomycin* - Streptomycin, an aminoglycoside, primarily causes **ototoxicity** (hearing loss, vertigo) and **nephrotoxicity**. - It is not implicated in drug-induced lupus erythematosus. *Rifampicin* - Rifampicin's notable side effects include **hepatotoxicity**, **red-orange discoloration of body fluids**, and **gastrointestinal upset**. - While rifampicin can rarely cause drug-induced lupus, **isoniazid is a far more common cause** and is the more likely culprit given the classic DILE presentation with anti-histone antibodies.

Question 242: A 62-year-old man comes to the physician because of a 5-day history of fatigue, fever, and chills. For the past 9 months, he has had hand pain and stiffness that has progressively worsened. He started a new medication for these symptoms 3 months ago. Medications used prior to that included ibuprofen, prednisone, and hydroxychloroquine. He does not smoke or drink alcohol. Examination shows a subcutaneous nodule at his left elbow, old joint destruction with boutonniere deformity, and no active joint warmth or tenderness. The remainder of the physical examination shows no abnormalities. His hemoglobin concentration is 10.5 g/dL, leukocyte count is 3500/mm3, and platelet count is 100,000/mm3. Which of the following is most likely to have prevented this patient's laboratory abnormalities?

A. Amifostine
B. Pyridoxine
C. Mesna
D. Leucovorin (Correct Answer)
E. Cobalamin

Explanation: ***Leucovorin*** - The patient's presentation with **fatigue, fever, chills, subcutaneous nodules, boutonniere deformity, and pancytopenia** strongly suggests **methotrexate toxicity**, likely from the new medication started 3 months ago for his worsening hand pain and stiffness. - **Leucovorin** (folinic acid) is used as a "rescue" treatment to replenish folate stores and **prevent myelosuppression, mucositis, and gastrointestinal toxicity** associated with methotrexate, which inhibits **dihydrofolate reductase**. *Amifostine* - **Amifostine** is a cytoprotective agent primarily used to reduce **renal toxicity** associated with platinum-based chemotherapy and salivary gland dysfunction from radiation therapy. - It does not specifically reverse or prevent the myelosuppressive effects of methotrexate. *Pyridoxine* - **Pyridoxine (Vitamin B6)** is important for various metabolic functions and is used to prevent **neuropathy** associated with certain drugs like isoniazid. - It has no role in preventing the hematologic or gastrointestinal toxicities of methotrexate. *Mesna* - **Mesna** is a uroprotectant agent used to prevent **hemorrhagic cystitis** caused by oxazaphosphorine chemotherapy agents like cyclophosphamide and ifosfamide. - It does not mitigate the side effects of methotrexate. *Cobalamin* - **Cobalamin (Vitamin B12)** is crucial for DNA synthesis and neurologic function; its deficiency can lead to **macrocytic anemia and neurological symptoms**. - While important for hematopoiesis, it does not directly counteract the mechanism of methotrexate toxicity or prevent its myelosuppressive effects.

Question 243: A patient with HCC and a long history of alcohol dependence and chronic hepatitis C has been using the mTOR inhibitor sirolimus 100 mg for cancer treatment. Her cancer has shown a partial response. She also has a history of hypertension and poorly controlled type 2 diabetes mellitus complicated by diabetic retinopathy. Current medications include enalapril and insulin. She asks her oncologist and hepatologist if she could try everolimus for its purported survival benefit in treating HCC. Based on clinical considerations, which of the following statements is most accurate?

A. The patient should start everolimus 50 mg because of the survival benefit relative to sirolimus 100 mg
B. The patient is not a good candidate for everolimus due to her history of hypertension
C. The patient should start everolimus 100 mg because of the survival benefit relative to sirolimus 100 mg
D. The patient should start everolimus 50 mg because of her history of alcohol use disorder and hepatitis C
E. The patient is not a good candidate for everolimus due to her history of diabetes (Correct Answer)

Explanation: ***The patient is not a good candidate for Noxbinle due to her history of diabetes*** - The current medication is sirolimus, an **mTOR inhibitor** and its successor everolimus, also an mTOR inhibitor, is not beneficial for this patient due to her **poorly controlled type 2 diabetes mellitus**. - mTOR inhibitors, including everolimus, are known to **worsen hyperglycemia** and **accelerate the progression of diabetes**, making it contraindicated in patients with already complicated diabetes. *The patient should start everolimus 50 mg because of the survival benefit relative to sirolimus 100 mg* - There is **no established evidence** that everolimus at any dose offers a superior survival benefit compared to sirolimus in HCC, particularly after a partial response to sirolimus. - **Switching mTOR inhibitors** without a compelling clinical reason, especially with existing comorbidities, is not standard practice. *The patient is not a good candidate for everolimus due to her history of hypertension* - While mTOR inhibitors can contribute to **hypertension**, this patient is already on **enalapril** for her existing hypertension. - Her **poorly controlled diabetes** presents a more direct and severe contraindication due to the metabolic side effects of everolimus. *The patient should start everolimus 100 mg because of the survival benefit relative to sirolimus 100 mg* - No clinical data supports a **superior survival benefit** of everolimus 100 mg over sirolimus 100 mg in HCC. - Given the patient's existing **poorly controlled diabetes**, increasing the dose of an mTOR inhibitor or switching to an equivalent dose of another would heighten the risk of severe metabolic complications. *The patient should start everolimus 50 mg because of her history of alcohol use disorder and hepatitis C* - The patient's history of alcohol dependence and chronic hepatitis C are **risk factors for HCC** but do not directly contraindicate a specific dose of everolimus more than her diabetes. - While liver impairment due to these conditions might influence dosing of various medications, the **primary concern for everolimus** in this case remains the uncontrolled diabetes.

Question 244: A general surgery intern is paged to the bedside of a 59-year-old male who underwent a successful sigmoidectomy for treatment of recurrent diverticulitis. The patient's nurse just recorded a temperature of 38.7 C, and relates that the patient is complaining of chills. The surgery was completed 8 hours ago and was complicated by extensive bleeding, with an estimated blood loss of 1,700 mL. Post-operative anemia was diagnosed after a hemoglobin of 5.9 g/dL was found; 2 units of packed red blood cells were ordered, and the transfusion was initiated 90 minutes ago. The patient's vital signs are as follows: T 38.7 C, HR 88, BP 138/77, RR 18, SpO2 98%. Physical examination does not show any abnormalities. After immediately stopping the transfusion, which of the following is the best management of this patient's condition?

A. Hydrate with 1 L bolus of normal saline followed by maintenance fluids at 125 cc/hr
B. Prescribe diphenhydramine
C. Monitor patient and administer acetaminophen (Correct Answer)
D. Start supplemental oxygen by nasal cannula
E. Initiate broad spectrum antibiotics

Explanation: ***Monitor patient and administer acetaminophen*** - This patient is experiencing a **febrile non-hemolytic transfusion reaction (FNHTR)**, characterized by a temperature increase of ≥1°C during or within hours of transfusion, and chills, in the absence of other causes. **Acetaminophen** is the primary treatment for fever and discomfort, and careful monitoring is crucial to rule out more severe reactions. - The patient's vital signs are otherwise stable, and there are no signs of anaphylaxis, hemolysis, or bacterial contamination, making supportive care with antipyretics the most appropriate initial management after stopping the transfusion. *Hydrate with 1 L bolus of normal saline followed by maintenance fluids at 125 cc/hr* - While hydration is generally important post-surgery, there is **no indication of hypovolemia or dehydration** (BP 138/77, HR 88, SpO2 98%) that would necessitate an immediate fluid bolus for this specific reaction. - Excessive fluid administration could potentially worsen underlying cardiac conditions or lead to fluid overload, especially in an elderly patient. *Prescribe diphenhydramine* - **Diphenhydramine** (an antihistamine) is primarily used for **allergic transfusion reactions**, which typically present with urticaria, pruritus, or respiratory symptoms like wheezing, none of which are observed in this patient. - This patient's symptoms are fever and chills, not allergic manifestations. *Start supplemental oxygen by nasal cannula* - The patient's **oxygen saturation is 98%**, indicating he is not hypoxic. - There is no clinical sign of respiratory distress or hypoxemia that would warrant supplemental oxygen. *Initiate broad spectrum antibiotics* - While fever is present, there is **no evidence of bacterial infection** (e.g., hypotension, rapid deterioration, signs of sepsis) that would require immediate broad-spectrum antibiotics for a transfusion reaction at this early stage. - Unnecessary antibiotic use contributes to antibiotic resistance and can have side effects.

Question 245: You are seeing a patient in clinic who recently started treatment for active tuberculosis. The patient is currently being treated with rifampin, isoniazid, pyrazinamide, and ethambutol. The patient is not used to taking medicines and is very concerned about side effects. Specifically regarding the carbohydrate polymerization inhibiting medication, which of the following is a known side effect?

A. Vision loss (Correct Answer)
B. Paresthesias of the hands and feet
C. Cutaneous flushing
D. Arthralgias
E. Elevated liver enzymes

Explanation: ***Vision loss*** - The "carbohydrate polymerization inhibiting medication" refers to **ethambutol**, which inhibits **arabinosyl transferase** (involved in mycobacterial cell wall arabinogalactan synthesis) - **Ethambutol** causes **optic neuritis**, leading to **decreased visual acuity**, **red-green color blindness**, and potentially **irreversible vision loss** - **Regular ophthalmologic monitoring** is essential during ethambutol therapy *Paresthesias of the hands and feet* - This describes **peripheral neuropathy** caused by **isoniazid** - Isoniazid interferes with **pyridoxine (vitamin B6) metabolism**, leading to neurotoxicity - Risk factors include malnutrition, diabetes, alcoholism, and pregnancy - Prevented by **pyridoxine supplementation** *Cutaneous flushing* - Not a characteristic side effect of first-line anti-tuberculosis medications - More commonly associated with niacin or certain allergic/vasodilatory reactions *Arthralgias* - Classic side effect of **pyrazinamide**, often affecting small joints - Caused by **pyrazinamide-induced hyperuricemia** (inhibits renal uric acid excretion) - May require dose adjustment or discontinuation if severe *Elevated liver enzymes* - **Hepatotoxicity** can occur with **rifampin**, **isoniazid**, and **pyrazinamide** - Requires regular monitoring of liver function tests during TB treatment - Most common serious adverse effect of combination TB therapy

Question 246: A 27-year-old man presents to his primary care physician for his first appointment. He recently was released from prison. The patient wants a checkup before he goes out and finds a job. He states that lately he has felt very fatigued and has had a cough. He has lost roughly 15 pounds over the past 3 weeks. He attributes this to intravenous drug use in prison. His temperature is 99.5°F (37.5°C), blood pressure is 127/68 mmHg, pulse is 100/min, respirations are 18/min, and oxygen saturation is 98% on room air. The patient is started on appropriate treatment. Which of the following is the most likely indication to discontinue this patient's treatment?

A. Optic neuritis
B. Peripheral neuropathy
C. Hyperuricemia
D. Elevated liver enzymes (Correct Answer)
E. Red body excretions

Explanation: ***Elevated liver enzymes*** - The patient's presentation (fatigue, cough, weight loss, history of IV drug use, prison exposure) is highly suggestive of **active tuberculosis (TB)**, which is typically treated with a multi-drug regimen including **isoniazid** and **rifampin**. - Both isoniazid and rifampin are associated with **hepatotoxicity**; significant elevation of liver enzymes (e.g., >5 times the upper limit of normal) is a strong indication to discontinue or modify the treatment regimen to prevent severe liver damage. *Optic neuritis* - **Ethambutol**, another first-line anti-TB drug, can cause **optic neuritis** (inflammation of the optic nerve) leading to vision changes or loss. - While a serious side effect requiring discontinuation of ethambutol, it is specific to that drug and not a general indication to stop all anti-TB treatment as would be the case with widespread hepatotoxicity. *Peripheral neuropathy* - **Isoniazid** can cause **peripheral neuropathy** due to interference with pyridoxine (vitamin B6) metabolism. - This side effect can often be prevented or managed by co-administration of **pyridoxine** and does not typically necessitate discontinuation of isoniazid unless severe and unmanageable. *Hyperuricemia* - **Pyrazinamide**, another first-line TB drug, can cause **hyperuricemia** (elevated uric acid levels) by inhibiting urate excretion. - While it can precipitate **gouty arthritis**, hyperuricemia alone is generally not an indication to discontinue pyrazinamide unless symptoms are severe or progress to acute gout. *Red body excretions* - **Rifampin** commonly causes **red-orange discoloration of urine, sweat, tears, and other body fluids**, which is a harmless side effect. - This is an expected and benign pharmacological effect of the drug and does not warrant discontinuation of treatment.

Question 247: A 52-year-old farmer presents to his physician with a puncture wound on his left shin. He got this wound accidentally when he felt unwell and went out to his garden "to catch some air". He reports he had been treated for tetanus 35 years ago and has received the Tdap vaccine several times since then, but he does not remember when he last received the vaccine. His vital signs are as follows: the blood pressure is 110/80 mm Hg, heart rate is 91/min, respiratory rate is 19/min, and temperature is 37.8°C (100.0°F). On physical examination, he is mildly dyspneic and pale. Lung auscultation reveals diminished vesicular breath sounds in the lower lobes bilaterally with a few inspiratory crackles heard over the left lower lobe. There is a puncture wound 1 cm in diameter that is contaminated with soil in the middle third of the patient’s shin. You order blood tests and an X-ray, and now you are arranging his wound treatment. How should tetanus post-exposure prevention be performed in this case?

A. The patient should be administered only the Tdap vaccine, because it is a minor wound with a small area of possible toxin absorption.
B. The patient does not need tetanus post-exposure prevention, because he has a past medical history of tetanus.
C. The patient should receive both tetanus toxoid-containing vaccine and human tetanus immunoglobulin. (Correct Answer)
D. The patient does not need tetanus post-exposure prevention, because he received the Tdap vaccine several times in the past.
E. The patient should only be administered human tetanus immunoglobulin, because he is acutely ill and febrile, which are contraindications for tetanus toxoid-containing vaccine administration.

Explanation: ***The patient should receive both tetanus toxoid-containing vaccine and human tetanus immunoglobulin.*** - This patient has a **tetanus-prone wound** (puncture wound contaminated with soil) and an **uncertain vaccination history** (due to not remembering when the last Tdap was). - For clean wounds, a Tdap booster within 5 years is sufficient, but with a dirty wound and uncertain history, **both passive immunization (tetanus immunoglobulin) and active immunization (Tdap vaccine)** are required. *The patient should be administered only the Tdap vaccine, because it is a minor wound with a small area of possible toxin absorption.* - A **puncture wound contaminated with soil** is considered a tetanus-prone wound, regardless of size, requiring more aggressive prophylaxis. - Relying solely on the vaccine may not provide immediate protection, as it takes time for the body to mount an **immune response**. *The patient does not need tetanus post-exposure prevention, because he has a past medical history of tetanus.* - A past history of tetanus **does not confer lifelong immunity** due to the low toxin dose required to cause disease, which is insufficient to stimulate a robust immune response. - Thus, previous tetanus infection does not negate the need for **vaccination or passive immunity** following injury. *The patient does not need tetanus post-exposure prevention, because he received the Tdap vaccine several times in the past.* - While he received the vaccine "several times," the **exact timing of his last dose is unknown**, which is critical for determining protection levels. - Without a clear history of a booster within the last **5 years for dirty wounds** or 10 years for clean wounds, his immune status is considered uncertain. *The patient should only be administered human tetanus immunoglobulin, because he is acutely ill and febrile, which are contraindications for tetanus toxoid-containing vaccine administration.* - **Mild illness or low-grade fever** is generally not a contraindication for vaccination, and the potential benefits often outweigh the risks in post-exposure prophylaxis. - While **tetanus immunoglobulin** provides immediate passive protection, it does not stimulate long-term active immunity, which is crucial for ongoing protection.

Question 248: Nucleic acid amplification testing (NAAT) of first-void urine confirms infection with Chlamydia trachomatis. Treatment with the appropriate pharmacotherapy is started. Which of the following health maintenance recommendations is most appropriate at this time?

A. Take medication with food
B. Avoid sun exposure
C. Avoid drinking alcohol
D. Avoid sexual activity for the next month (Correct Answer)
E. Schedule an ophthalmology consultation

Explanation: ***Avoid sexual activity for the next month*** - **CDC guidelines** recommend abstinence from sexual activity until 7 days after treatment completion AND until all sexual partners have been treated and cured. The recommendation of "the next month" provides adequate time to ensure both conditions are met, as **partner notification**, testing, and treatment often takes several weeks. - This is the **most important health maintenance recommendation** as preventing **reinfection** and further **transmission** is the primary public health concern, superseding medication-specific advice. *Take medication with food* - This recommendation is specific to certain antibiotics to reduce gastrointestinal upset or improve absorption, but it is not a universal health maintenance recommendation for all Chlamydia treatments (e.g., **azithromycin** can be taken with or without food; **doxycycline** should be taken with food to reduce GI upset, but not milk products). - While relevant to **medication adherence**, it is not the most crucial health maintenance advice regarding preventing transmission or re-infection. *Avoid sun exposure* - This advice is primarily given for medications that cause **photosensitivity**, such as **doxycycline**, which is a common treatment for Chlamydia. - However, it's not applicable to all Chlamydia treatments (e.g., **azithromycin**) and is not the most critical health recommendation in the context of preventing disease transmission. *Avoid drinking alcohol* - This is a general recommendation for many antibiotic treatments to prevent potential interactions or increased side effects, but it is not a specific contraindication for the primary antibiotics used for Chlamydia. - **Metronidazole**, used for other STIs (e.g., trichomoniasis), has a strong interaction with alcohol. However, it's not the primary treatment for Chlamydia, making this recommendation less universally appropriate here. *Schedule an ophthalmology consultation* - While Chlamydia can cause **conjunctivitis** (ophthalmia neonatorum in newborns or adult inclusion conjunctivitis), it is not a typical complication requiring routine ophthalmology consultation unless specific **ocular symptoms** are present. - This recommendation is not a standard health maintenance strategy for **uncomplicated Chlamydia infections**.

Question 249: A 5-year-old boy presents with altered mental status and difficulty breathing for the past couple of hours. The patient’s father, a mechanic, says the boy accidentally ingested an unknown amount of radiator fluid. The patient’s vital signs are: temperature 37.1°C (98.8.F), pulse 116/min, blood pressure 98/78 mm Hg, and respiratory rate 42/min. On physical examination, cardiopulmonary auscultation reveals deep, rapid respirations with no wheezing, rhonchi, or crepitations. An ABG reveals the blood pH to be 7.2 with an anion gap of 16 mEq/L. Urinalysis reveals the presence of oxalate crystals. Which of the following is the most appropriate antidote for the poison that this patient has ingested?

A. Methylene blue
B. Dimercaprol
C. Flumazenil
D. Fomepizole (Correct Answer)
E. Succimer

Explanation: ***Fomepizole*** - The patient's presentation with **altered mental status**, **deep, rapid respirations (Kussmaul breathing)**, **anion gap metabolic acidosis**, and **oxalate crystals in the urine** are classic signs of **ethylene glycol poisoning**. Fomepizole acts by **inhibiting alcohol dehydrogenase**, which is the enzyme responsible for metabolizing ethylene glycol into its toxic metabolites (glycolic acid and oxalic acid). - This inhibition prevents the formation of these toxic compounds, thereby reducing organ damage and metabolic acidosis. *Methylene blue* - **Methylene blue** is used to treat **methemoglobinemia**, a condition where iron in hemoglobin is oxidized, reducing oxygen-carrying capacity. Symptoms include cyanosis and shortness of breath, but it is not associated with anion gap metabolic acidosis or oxalate crystals. - Its mechanism of action involves acting as an electron acceptor to reduce methemoglobin back to hemoglobin. *Dimercaprol* - **Dimercaprol** is a **chelating agent** primarily used in the treatment of **heavy metal poisoning**, such as arsenic, mercury, and gold. - It works by binding to metal ions, facilitating their excretion from the body, and is not indicated for ethylene glycol toxicity. *Flumazenil* - **Flumazenil** is a **GABA receptor antagonist** used to reverse the effects of **benzodiazepine overdose**. - Its primary action is to competitively inhibit the binding of benzodiazepines to GABA receptors in the central nervous system, thereby reversing sedation and respiratory depression due to benzodiazepines. *Succimer* - **Succimer** (2,3-dimercaptosuccinic acid) is an **oral chelating agent** used to treat **lead poisoning** and other heavy metal toxicities, similar to dimercaprol. - It forms stable complexes with heavy metals, facilitating their urinary excretion. It is not indicated for ethylene glycol poisoning.

Question 250: Three days after starting a new drug for malaria prophylaxis, a 19-year-old college student comes to the physician because of dark-colored urine and fatigue. He has not had any fever, dysuria, or abdominal pain. He has no history of serious illness. Physical examination shows scleral icterus. Laboratory studies show a hemoglobin of 9.7 g/dL and serum lactate dehydrogenase of 234 U/L. Peripheral blood smear shows poikilocytes with bite-shaped irregularities. Which of the following drugs has the patient most likely been taking?

A. Dapsone
B. Doxycycline
C. Primaquine (Correct Answer)
D. Ivermectin
E. Pyrimethamine

Explanation: ***Primaquine*** - The patient's symptoms, including **dark urine**, **fatigue**, **scleral icterus**, **anemia** (hemoglobin 9.7 g/dL), elevated **LDH**, and **bite cells** on peripheral smear, are classic signs of **acute hemolytic anemia**. - **Primaquine** is an antimalarial drug known to cause oxidative stress, leading to hemolysis in individuals with **glucose-6-phosphate dehydrogenase (G6PD) deficiency**. The "bite cells" are a hallmark of G6PD deficiency, as they result from the spleen removing Heinz bodies (oxidized hemoglobin). *Dapsone* - While **dapsone** can also cause **hemolytic anemia** in G6PD-deficient patients due to its oxidative properties, it is **not used for malaria prophylaxis**. - Dapsone is primarily used for conditions like leprosy, dermatitis herpetiformis, and Pneumocystis pneumonia prophylaxis, making it an unlikely choice in this clinical scenario. *Doxycycline* - **Doxycycline** is a tetracycline antibiotic commonly used for malaria prophylaxis. - Its common side effects include **photosensitivity**, **gastrointestinal upset**, and **esophageal irritation**, but it does not typically cause hemolytic anemia or bite cells. *Ivermectin* - **Ivermectin** is an antiparasitic drug used for conditions like onchocerciasis, strongyloidiasis, and scabies, but **not for malaria prophylaxis**. - Side effects usually involve **neurological symptoms**, **skin reactions**, and **gastrointestinal disturbances**, but not hemolytic anemia. *Pyrimethamine* - **Pyrimethamine** is an antifolate drug used in combination with other drugs for malaria treatment and prophylaxis. - Its primary adverse effects relate to **bone marrow suppression** (e.g., megaloblastic anemia, leukopenia), not hemolytic anemia or bite cells.

Question 251: A 67-year-old woman with advanced bladder cancer comes to the physician for a follow-up examination. She is currently undergoing chemotherapy with an agent that forms cross-links between DNA strands. Serum studies show a creatinine concentration of 2.1 mg/dL and a blood urea nitrogen concentration of 30 mg/dL. Urine dipstick of a clean-catch midstream specimen shows 2+ protein and 1+ glucose. Prior to initiation of chemotherapy, her laboratory values were within the reference range. In addition to hydration, administration of which of the following would most likely have prevented this patient's current condition?

A. Leucovorin
B. Amifostine (Correct Answer)
C. Aprepitant
D. Mesna
E. Rasburicase

Explanation: **Amifostine** - This patient's symptoms (elevated creatinine and BUN, 2+ protein, 1+ glucose in urine) suggest **renal tubular damage**, specifically acute tubular necrosis, likely caused by a nephrotoxic chemotherapeutic agent. - **Amifostine** is a cytoprotective agent that scavenges reactive oxygen species in local tissues, thereby reducing the nephrotoxic effects of **alkylating agents** like cisplatin, which forms cross-links between DNA strands. *Leucovorin* - **Leucovorin** (folinic acid) is used to rescue normal cells from the adverse effects of **methotrexate**, enhancing its excretion and reducing toxicity. - It is not indicated for preventing kidney damage from DNA cross-linking agents. *Aprepitant* - **Aprepitant** is a neurokinin-1 (NK1) receptor antagonist used to prevent **chemotherapy-induced nausea and vomiting**. - It does not have protective effects against nephrotoxicity. *Mesna* - **Mesna** (2-mercaptoethane sulfonate sodium) is used to prevent **hemorrhagic cystitis** caused by acrolein, a toxic metabolite of cyclophosphamide and ifosfamide. - It does not prevent nephrotoxicity from other types of chemotherapy agents. *Rasburicase* - **Rasburicase** is a recombinant urate oxidase enzyme used to prevent or treat **tumor lysis syndrome** by converting uric acid to allantoin, which is more soluble and easily excreted. - It is not used for preventing direct kidney damage from chemotherapeutic agents.

Question 252: A 52-year-old man presents for a routine checkup. Past medical history is remarkable for stage 1 systemic hypertension and hepatitis A infection diagnosed 10 years ago. He takes aspirin, rosuvastatin, enalapril daily, and a magnesium supplement every once in a while. He is planning to visit Ecuador for a week-long vacation and is concerned about malaria prophylaxis before his travel. The physician advised taking 1 primaquine pill every day while he is there and for 7 consecutive days after leaving Ecuador. On the third day of his trip, the patient develops an acute onset headache, dizziness, shortness of breath, and fingertips and toes turning blue. His blood pressure is 135/80 mm Hg, heart rate is 94/min, respiratory rate is 22/min, temperature is 36.9℃ (98.4℉), and blood oxygen saturation is 97% in room air. While drawing blood for his laboratory workup, the nurse notes that his blood has a chocolate brown color. Which of the following statements best describes the etiology of this patient’s most likely condition?

A. The patient’s condition is due to consumption of water polluted with nitrates.
B. The patient had pre-existing liver damage caused by viral hepatitis.
C. This condition resulted from primaquine overdose.
D. It is a type B adverse drug reaction. (Correct Answer)
E. The condition developed because of his concomitant use of primaquine and magnesium supplement.

Explanation: ***It is a type B adverse drug reaction.*** - The patient's symptoms (headache, dizziness, shortness of breath, cyanosis, chocolate brown blood) are consistent with **methemoglobinemia**, which is a known idiosyncratic reaction to **primaquine**. Type B adverse drug reactions are **unpredictable** and not dose-dependent, representing an individual's unique response to a drug. - This reaction likely stems from an underlying **glucose-6-phosphate dehydrogenase (G6PD) deficiency**, making him susceptible to oxidative stress induced by primaquine, leading to methemoglobin formation. The occurrence of symptoms early in the course of medication (3rd day) also supports an idiosyncratic reaction rather than a typical dose-related effect. *The patient’s condition is due to consumption of water polluted with nitrates.* - While **nitrate poisoning** can cause methemoglobinemia, the patient’s symptoms appeared shortly after starting primaquine for malaria prophylaxis, making drug-induced methemoglobinemia a more direct and probable cause in this clinical context. - Exposure to nitrate-polluted water is unlikely to cause a sudden onset of such severe symptoms within 3 days of arrival, especially considering he is taking a known oxidizing agent (primaquine). *The patient had pre-existing liver damage caused by viral hepatitis.* - Although **liver dysfunction** can alter drug metabolism, hepatitis A is an acute infection that does not typically cause chronic liver damage leading to altered drug metabolism for primaquine in the long term, especially 10 years after diagnosis. - The primary risk factor for primaquine-induced methemoglobinemia is G6PD deficiency, not liver damage, which affects red blood cell susceptibility to oxidative stress. *This condition resulted from primaquine overdose.* - The prescribed dose of primaquine (one pill daily) is standard for malaria prophylaxis, and there is no indication the patient took more than prescribed. This reaction is likely due to an **idiosyncratic response** rather than an excessive dose. - Methemoglobinemia from primaquine is often seen in individuals with **G6PD deficiency** even at therapeutic doses, making it an unpredictable Type B adverse reaction rather than a direct dose-dependent toxicity. *The condition developed because of his concomitant use of primaquine and magnesium supplement.* - There is no known direct significant **drug interaction** between primaquine and magnesium supplements that would lead to methemoglobinemia. - The underlying cause of methemoglobinemia with primaquine is typically due to its **oxidative properties** in susceptible individuals (e.g., G6PD deficiency), not an interaction with magnesium.

Question 253: A 70-year-old man presents to a medical clinic reporting blood in his urine and lower abdominal pain for the past few days. He is also concerned about urinary frequency and urgency. He states that he recently completed a cycle of chemotherapy for non-Hodgkin lymphoma. Which medication in the chemotherapy regimen most likely caused his symptoms?

A. Cyclophosphamide (Correct Answer)
B. Rituximab
C. Prednisone
D. Methotrexate
E. Cytarabine

Explanation: ***Cyclophosphamide*** - **Cyclophosphamide** is an alkylating agent commonly used in the **R-CHOP regimen** (standard treatment for non-Hodgkin lymphoma) and is known to cause **hemorrhagic cystitis** due to the accumulation of its metabolite **acrolein** in the bladder. - This leads to symptoms like **blood in urine (hematuria)**, lower abdominal pain, urinary frequency, and urgency. - This toxicity can be mitigated by co-administering **mesna** (2-mercaptoethane sulfonate sodium) and ensuring adequate hydration to prevent bladder irritation. *Rituximab* - **Rituximab** is a **monoclonal antibody** targeting CD20 on B-cells, the "R" in R-CHOP, primarily associated with **infusion reactions**, B-cell depletion, and increased risk of infections. - It does not typically cause direct **bladder toxicity** or hemorrhagic cystitis. *Prednisone* - **Prednisone** is a corticosteroid (the "P" in R-CHOP) commonly used in lymphoma regimens to induce apoptosis in lymphoid cells and manage side effects of chemotherapy. - Its side effects include **immunosuppression**, hyperglycemia, and gastric irritation, but not usually hemorrhagic cystitis. *Methotrexate* - **Methotrexate** is an antimetabolite that inhibits dihydrofolate reductase and is commonly associated with **myelosuppression**, mucositis, and nephrotoxicity at high doses. - While it can affect the kidneys and is sometimes used in certain lymphoma regimens, it is not a primary cause of **hemorrhagic cystitis**. *Cytarabine* - **Cytarabine** is an antimetabolite primarily used in leukemias and some aggressive lymphomas, known for causing **myelosuppression**, mucositis, and cerebellar toxicity at high doses. - It is not typically associated with **hemorrhagic cystitis** or bladder irritation.

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