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?
Q262
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?
Q263
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?
Q264
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?
Q265
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?
Q266
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?
Q267
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?
Q268
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?
Q269
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?
Antimicrobials US Medical PG Practice Questions and MCQs
Question 261: 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 262: 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 263: 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 264: 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 265: 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 266: 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 267: 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 268: 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 269: 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.
