A 53-year-old woman presents to her primary care physician due to her "feet feeling painful." She reports initially having decreased sensation on both of her feet and recently her hands. She now experiences paresthesias, numbness, and a "burning pain." She is recovering from a recent myocardial infarction. Approximately 1.5 weeks ago, she experienced mild watery diarrhea and an atypical pneumonia. For the past 3 weeks, she has been experiencing fatigue, trouble with concentration, and mild weight gain. Beyond this she has no other acute concerns. Her past medical history is significant for type II diabetes mellitus, hypertension, and coronary artery disease. She is currently taking metformin, aspirin, atorvastatin, metoprolol, and lisinopril. Her temperature is 99°F (37.2°C), blood pressure is 155/98 mmHg, pulse is 85/min, and respirations are 14/min. On physical exam, there is a loss of vibratory sensation and altered proprioception in the bilateral feet. She has impaired pain, light touch, and temperature sensation starting from her feet to mid-calf and hands. She has normal strength and muscle tone throughout her upper and lower extremities, as well as absent bilateral ankle reflexes. Which of the following is the best next step in management?
Q332
A 22-year-old female presents to her PCP after having unprotected sex with her boyfriend 2 days ago. She has been monogamous with her boyfriend but is very concerned about pregnancy. The patient requests emergency contraception to decrease her likelihood of getting pregnant. A blood hCG test returns negative. The PCP prescribes the patient ethinyl estradiol 100 mcg and levonorgestrel 0.5 mg to be taken 12 hours apart. What is the most likely mechanism of action for this combined prescription?
Q333
A 49-year-old woman presents to her primary care physician with fatigue. She reports that she has recently been sleeping more than usual and says her “arms and legs feel like lead” for most of the day. She has gained 10 pounds over the past 3 months which she attributes to eating out at restaurants frequently, particularly French cuisine. Her past medical history is notable for social anxiety disorder. She took paroxetine and escitalopram in the past but had severe nausea and headache while taking both. She has a 10 pack-year smoking history and has several glasses of wine per day. Her temperature is 98.6°F (37°C), blood pressure is 130/65 mmHg, pulse is 78/min, and respirations are 16/min. Physical examination reveals an obese woman with a dysphoric affect. She states that her mood is sad but she does experience moments of happiness when she is with her children. The physician starts the patient on a medication to help with her symptoms. Three weeks after the initiation of the medication, the patient presents to the emergency room with a severe headache and agitation. Her temperature is 102.1°F (38.9°C), blood pressure is 180/115 mmHg, pulse is 115/min, and respirations are 24/min. Which of the following is the mechanism of action of the medication that is most likely responsible for this patient’s symptoms?
Q334
A 3-year-old boy is brought to the emergency department by his mother. His mother reports that she found him playing under the sink yesterday. She was concerned because she keeps some poisons for pest control under the sink but did not believe that he came in contact with the poisons. However, this morning the boy awoke with abdominal pain and epistaxis, causing her to rush him to the emergency department.
You obtain stat lab-work with the following results:
WBC: 6,000/microliter;
Hgb: 11.2 g/dL;
Platelets: 200,000/microliter;
PTT: 35 seconds;
INR: 6.5;
Na: 140 mEq/L;
K: 4 mEq/L;
Cr: 0.7 mg/dL.
Which of the following is likely to be the most appropriate treatment?
Q335
A 66-year-old female presents to the emergency room with left hip pain after a fall. She is unable to move her hip due to pain. On exam, her left leg appears shortened and internally rotated. Hip radiographs reveal a fracture of the left femoral neck. She has a history of a distal radius fracture two years prior. Review of her medical record reveals a DEXA scan from two years ago that demonstrated a T-score of -3.0. Following acute management of her fracture, she is started on a medication that is known to induce osteoclast apoptosis. Which of the following complications is most closely associated with the medication prescribed in this case?
Q336
A 43-year-old man comes to the physician because of anxiety, difficulty focusing on tasks, and a 4.6-kg (10-lb) weight loss over the past 4 weeks. He is diaphoretic. His pulse is 100/min, respirations are 18/min, and blood pressure is 150/78 mm Hg. Physical examination shows warm, moist skin, goiter, and a resting tremor of both hands. Laboratory studies show a thyroxine (T4) concentration of 30 μg/dL and a thyroid-stimulating hormone concentration of 0.1 μU/mL. The patient is started on methimazole and atenolol. The latter agent predominantly affects which of the following?
Q337
A 53-year-old woman comes to the physician because of increasing shortness of breath on exertion for 5 months. She reports that she can not climb more than 2 flights of stairs and she is no longer able to run her errands as usual. One year ago, she was diagnosed with triple-negative breast cancer. She underwent a right-sided modified radical mastectomy and adjuvant chemotherapy. Cardiac examination shows a laterally displaced point of maximal impulse. Coarse inspiratory crackles are heard in both lower lung fields. Echocardiography shows a left ventricular ejection fraction of 30%. The physician informs the patient that her symptoms are most likely due to an adverse effect of her chemotherapy. The drug most likely responsible for the patient's current symptoms belongs to which of the following groups of agents?
Q338
A 68-year-old man with type 2 diabetes mellitus comes to the physician because of a 5-month history of episodic palpitations, dizziness, and fatigue. His pulse is 134/min and irregularly irregular, and his blood pressure is 165/92 mm Hg. An ECG shows a narrow complex tachycardia with absent P waves. He is prescribed a drug that decreases the long-term risk of thromboembolic complications by inhibiting the extrinsic pathway of the coagulation cascade. The expected beneficial effect of this drug is most likely due to which of the following actions?
Q339
An 11-year-old boy is brought to the physician by his mother because of a pruritic generalized rash for 2 days. He returned from a 3-day outdoor summer camp 1 week ago. During his time there, one child was sent home after being diagnosed with measles. The patient was diagnosed with a seizure disorder 6 weeks ago and he has asthma. Current medications include carbamazepine and an albuterol inhaler. His immunization records are unavailable. His temperature is 38.4°C (101.1°F), pulse is 88/min, and blood pressure is 102/60 mm Hg. Examination shows facial edema and a diffuse rash over the face, trunk, and extremities. There is cervical and inguinal lymphadenopathy. The remainder of the examination shows no abnormalities. Which of the following is the most appropriate next step in management?
Q340
A 35-year-old woman is admitted to the medical unit for worsening renal failure. Prior to admission, she was seen by her rheumatologist for a follow-up visit and was found to have significant proteinuria and hematuria on urinalysis and an elevated serum creatinine. She reports feeling ill and has noticed blood in her urine. She was diagnosed with systemic lupus erythematosus at the age of 22, and she is currently being treated with ibuprofen for joint pain and prednisone for acute flare-ups. Her blood pressure is 165/105 mmHg. Laboratory testing is remarkable for hypocomplementemia and an elevated anti-DNA antibody. A renal biopsy is performed, which demonstrates 65% glomerular involvement along with the affected glomeruli demonstrating endocapillary and extracapillary glomerulonephritis. In addition to glucocorticoid therapy, the medical team will add mycophenolate mofetil to her treatment regimen. Which of the following is the mechanism of action of mycophenolate mofetil?
Autonomic/CV Drugs US Medical PG Practice Questions and MCQs
Question 331: A 53-year-old woman presents to her primary care physician due to her "feet feeling painful." She reports initially having decreased sensation on both of her feet and recently her hands. She now experiences paresthesias, numbness, and a "burning pain." She is recovering from a recent myocardial infarction. Approximately 1.5 weeks ago, she experienced mild watery diarrhea and an atypical pneumonia. For the past 3 weeks, she has been experiencing fatigue, trouble with concentration, and mild weight gain. Beyond this she has no other acute concerns. Her past medical history is significant for type II diabetes mellitus, hypertension, and coronary artery disease. She is currently taking metformin, aspirin, atorvastatin, metoprolol, and lisinopril. Her temperature is 99°F (37.2°C), blood pressure is 155/98 mmHg, pulse is 85/min, and respirations are 14/min. On physical exam, there is a loss of vibratory sensation and altered proprioception in the bilateral feet. She has impaired pain, light touch, and temperature sensation starting from her feet to mid-calf and hands. She has normal strength and muscle tone throughout her upper and lower extremities, as well as absent bilateral ankle reflexes. Which of the following is the best next step in management?
A. Amitriptyline
B. Lidocaine patch
C. Gabapentin (Correct Answer)
D. Venlafaxine
E. Intravenous immunoglobulin
Explanation: ***Gabapentin***
- The patient's symptoms (paresthesias, numbness, burning pain, loss of vibratory sensation, impaired pain/light touch/temperature, absent ankle reflexes) are highly suggestive of **neuropathic pain**, likely from a **peripheral neuropathy**.
- **Gabapentin** is a first-line agent for the treatment of neuropathic pain, working by modulating voltage-gated calcium channels to reduce neurotransmitter release, effectively alleviating symptoms like burning and tingling.
*Amitriptyline*
- **Amitriptyline** is a tricyclic antidepressant (TCA) that can be used for neuropathic pain. However, it is generally considered a second-line agent due to its significant **anticholinergic side effects** (e.g., dry mouth, constipation, sedation) as well as cardiac side effects, which might be problematic for a patient with a history of coronary artery disease and recent MI.
*Lidocaine patch*
- **Lidocaine patches** provide topical analgesia and are primarily used for **localized neuropathic pain**, such as postherpetic neuralgia or localized diabetic neuropathy. The patient's symptoms are described as bilateral and diffuse, affecting both feet and hands, making a topical treatment less suitable as a sole initial therapeutic approach.
*Venlafaxine*
- **Venlafaxine** is a serotonin-norepinephrine reuptake inhibitor (SNRI) that is also used for neuropathic pain. While it is an effective option, especially when co-occurring depression is present, current guidelines often favor gabapentin or pregabalin as first-line agents due to a generally more favorable side effect profile and ease of titration, particularly in a patient with cardiovascular history.
*Intravenous immunoglobulin*
- **Intravenous immunoglobulin (IVIG)** is a treatment reserved for serious autoimmune neuropathies such as **Guillain-Barré Syndrome** or severe chronic inflammatory demyelinating polyneuropathy (CIDP). While the patient's symptoms could suggest an underlying neuropathy, there is no evidence of rapid progression or severe motor weakness that would indicate an acute inflammatory demyelinating process warranting IVIG.
Question 332: A 22-year-old female presents to her PCP after having unprotected sex with her boyfriend 2 days ago. She has been monogamous with her boyfriend but is very concerned about pregnancy. The patient requests emergency contraception to decrease her likelihood of getting pregnant. A blood hCG test returns negative. The PCP prescribes the patient ethinyl estradiol 100 mcg and levonorgestrel 0.5 mg to be taken 12 hours apart. What is the most likely mechanism of action for this combined prescription?
A. Inhibition or delayed ovulation (Correct Answer)
B. Interference of corpus luteum function
C. Thickening of cervical mucus with sperm trapping
D. Tubal constriction inhibiting sperm transportation
E. Alteration of the endometrium impairing implantation of the fertilized egg
Explanation: ***Inhibition or delayed ovulation***
- The high doses of **estrogen** and **progestin** in the combined emergency contraception pill primarily act by suppressing the **luteinizing hormone (LH) surge**, which is essential for ovulation.
- By inhibiting or delaying ovulation, the pill prevents the release of an egg, thus preventing fertilization since sperm cannot meet an egg.
*Interference of corpus luteum function*
- While hormonal contraceptives can affect the **corpus luteum**, high-dose emergency contraception primarily acts *before* the formation of a mature corpus luteum by preventing ovulation itself.
- Once the corpus luteum is formed, its function is usually maintained if pregnancy occurs, and emergency contraception given *after* implantation is generally ineffective at terminating a pregnancy.
*Thickening of cervical mucus with sperm trapping*
- This is a well-known mechanism of action for *continuous* hormonal contraception (e.g., daily birth control pills), where lower, consistent doses of progestin make cervical mucus impenetrable to sperm.
- While it might play a *minor* role, it is not the primary mechanism of action for high-dose emergency contraception administered acutely, which mainly targets ovulation.
*Tubal constriction inhibiting sperm transportation*
- There is no strong evidence to suggest that combined emergency contraception pills cause **tubal constriction** to significantly impair sperm or egg transport.
- The main sites of action are the **hypothalamic-pituitary-ovarian axis** (for ovulation) and possibly the endometrium (for implantation), not direct tubal motility.
*Alteration of the endometrium impairing implantation of the fertilized egg*
- While hormonal contraceptives can alter the **endometrium** making it less receptive to implantation, this is considered a *secondary* or less significant mechanism for combined emergency contraception.
- The primary goal and most effective action of these pills is to prevent fertilization by inhibiting ovulation, especially when taken shortly after unprotected intercourse and before implantation.
Question 333: A 49-year-old woman presents to her primary care physician with fatigue. She reports that she has recently been sleeping more than usual and says her “arms and legs feel like lead” for most of the day. She has gained 10 pounds over the past 3 months which she attributes to eating out at restaurants frequently, particularly French cuisine. Her past medical history is notable for social anxiety disorder. She took paroxetine and escitalopram in the past but had severe nausea and headache while taking both. She has a 10 pack-year smoking history and has several glasses of wine per day. Her temperature is 98.6°F (37°C), blood pressure is 130/65 mmHg, pulse is 78/min, and respirations are 16/min. Physical examination reveals an obese woman with a dysphoric affect. She states that her mood is sad but she does experience moments of happiness when she is with her children. The physician starts the patient on a medication to help with her symptoms. Three weeks after the initiation of the medication, the patient presents to the emergency room with a severe headache and agitation. Her temperature is 102.1°F (38.9°C), blood pressure is 180/115 mmHg, pulse is 115/min, and respirations are 24/min. Which of the following is the mechanism of action of the medication that is most likely responsible for this patient’s symptoms?
A. Inhibition of serotonin and norepinephrine reuptake
B. Inhibition of the adrenergic alpha-2 receptor and serotonin-2 and -3 receptors
C. Inhibition of serotonin reuptake
D. Partial agonism of serotonin-1A receptor
E. Inhibition of amine degradation (Correct Answer)
Explanation: **Inhibition of amine degradation**
- This mechanism of action describes **monoamine oxidase inhibitors (MAOIs)**. Given the patient's symptoms of **hypertensive crisis** (headache, agitation, hypertension, tachycardia, fever) after starting a new medication and her history of **eating French cuisine** (which could include tyramine-rich foods like aged cheeses and wines), an MAOI is the most likely culprit.
- MAOIs prevent the breakdown of **monoamine neurotransmitters** (serotonin, norepinephrine, dopamine, tyramine), leading to their accumulation. In the presence of **tyramine-rich foods**, this can precipitate a **hypertensive crisis** due to excessive norepinephrine release.
*Inhibition of serotonin and norepinephrine reuptake*
- This describes **SNRIs (serotonin-norepinephrine reuptake inhibitors)** or **TCAs (tricyclic antidepressants)**. While these can cause side effects, a sudden and severe **hypertensive crisis** as described, especially without a clear dietary trigger interaction, is less characteristic than with MAOIs.
- The patient's prior negative experiences with paroxetine and escitalopram (SSRIs) might make a physician choose a different class, but the dramatic symptoms point away from typical SNRI/TCA side effects for this presentation.
*Inhibition of the adrenergic alpha-2 receptor and serotonin-2 and -3 receptors*
- This mechanism is characteristic of **mirtazapine**. While mirtazapine can cause sedation and weight gain (presenting symptoms), it does not typically lead to a **hypertensive crisis** of this severity three weeks after initiation, nor does it have severe food interactions like MAOIs.
- Mirtazapine's primary side effects often include sedation, increased appetite, and weight gain, but not the acute constellation observed here.
*Inhibition of serotonin reuptake*
- This describes **SSRIs (selective serotonin reuptake inhibitors)**. The patient had severe nausea and headache with paroxetine and escitalopram, which are SSRIs. While SSRIs can contribute to **serotonin syndrome** (which shares some features like agitation and hyperthermia), the profound **hypertension** and context of food interaction strongly favor an MAOI-induced hypertensive crisis.
- SSRIs are less likely to cause such a severe **hypertensive crisis** acutely, and the patient's history suggests a physician would likely avoid this class due to past adverse reactions.
*Partial agonism of serotonin-1A receptor*
- This is the mechanism of action for **buspirone**, an anxiolytic. Buspirone is generally well-tolerated and does not cause the severe side effects seen in this patient, particularly **hypertensive crisis** or food interactions.
- Buspirone is often used for generalized anxiety disorder, and while the patient has social anxiety, the described adverse event does not align with buspirone's known side effect profile.
Question 334: A 3-year-old boy is brought to the emergency department by his mother. His mother reports that she found him playing under the sink yesterday. She was concerned because she keeps some poisons for pest control under the sink but did not believe that he came in contact with the poisons. However, this morning the boy awoke with abdominal pain and epistaxis, causing her to rush him to the emergency department.
You obtain stat lab-work with the following results:
WBC: 6,000/microliter;
Hgb: 11.2 g/dL;
Platelets: 200,000/microliter;
PTT: 35 seconds;
INR: 6.5;
Na: 140 mEq/L;
K: 4 mEq/L;
Cr: 0.7 mg/dL.
Which of the following is likely to be the most appropriate treatment?
A. Protamine sulfate
B. Dimercaptosuccinic acid (DMSA)
C. Packed red blood cells transfusion
D. Vitamin K and fresh frozen plasma (Correct Answer)
E. Penicillamine
Explanation: ***Vitamin K and fresh frozen plasma***
- The patient presents with **epistaxis** and a significantly **elevated INR (6.5)**, indicating a severe coagulopathy most likely due to **long-acting anticoagulant rodenticide poisoning** (superwarfarins like brodifacoum or bromadiolone found in pest control products). Vitamin K is the antidote, restoring normal clotting factor synthesis, while fresh frozen plasma provides immediate replacement of depleted clotting factors.
- The combination of vitamin K and fresh frozen plasma directly addresses the **bleeding risk** and coagulation defect, which is critical in acute warfarin toxicity. Note that superwarfarin poisoning requires **prolonged vitamin K therapy** (weeks to months) due to the long half-life of these rodenticides.
*Protamine sulfate*
- This is an antidote for **heparin overdose**, which directly inhibits thrombin and Factor Xa. The patient's elevated INR is indicative of warfarin-type poisoning, not heparin.
- Heparin toxicity is characterized by a prolonged **aPTT**, not primarily an elevated INR.
*Dimercaptosuccinic acid (DMSA)*
- DMSA is a **chelating agent** used to treat **heavy metal poisoning**, particularly **lead** and **mercury**. The patient's symptoms and lab results (elevated INR) are not consistent with heavy metal toxicity.
- There is no indication of heavy metal exposure or symptoms like neurological deficits or gastrointestinal distress typical of lead or mercury poisoning.
*Packed red blood cells transfusion*
- While the patient has epistaxis, the **hemoglobin level (11.2 g/dL)** is still within a relatively normal range, indicating no acute, severe blood loss requiring immediate packed red blood cell transfusion.
- Transfusing red blood cells would address anemia but would not correct the underlying **coagulopathy** or reverse the effects of the poison.
*Penicillamine*
- Penicillamine is a **chelating agent** used for **copper poisoning (Wilson's disease)**, **lead poisoning**, and sometimes **rheumatoid arthritis**. It is not indicated for coagulopathy from warfarin toxicity.
- The clinical picture and lab findings do not suggest heavy metal or copper toxicity, which would present with different symptoms and lab abnormalities.
Question 335: A 66-year-old female presents to the emergency room with left hip pain after a fall. She is unable to move her hip due to pain. On exam, her left leg appears shortened and internally rotated. Hip radiographs reveal a fracture of the left femoral neck. She has a history of a distal radius fracture two years prior. Review of her medical record reveals a DEXA scan from two years ago that demonstrated a T-score of -3.0. Following acute management of her fracture, she is started on a medication that is known to induce osteoclast apoptosis. Which of the following complications is most closely associated with the medication prescribed in this case?
A. Gingival hyperplasia
B. Vertebral compression fracture
C. Interstitial nephritis
D. Osteonecrosis of the jaw (Correct Answer)
E. Agranulocytosis
Explanation: ***Osteonecrosis of the jaw***
- The patient's history of a femoral neck fracture and a **DEXA T-score of -3.0** indicates **osteoporosis**, for which a medication inducing osteoclast apoptosis (e.g., **bisphosphonates** or **denosumab**) would be prescribed.
- **Osteonecrosis of the jaw (ONJ)** is a recognized, although rare, severe complication particularly associated with bisphosphonate and denosumab use, often following dental procedures.
*Gingival hyperplasia*
- This complication is most commonly associated with **calcium channel blockers** (like nifedipine), **cyclosporine**, and **phenytoin**.
- It is not a known side effect of medications that induce osteoclast apoptosis, such as bisphosphonates or denosumab.
*Vertebral compression fracture*
- While this patient is at high risk for osteoporotic fractures, medication that *treats* osteoporosis by inducing osteoclast apoptosis **reduces** the risk of new fractures, including vertebral compression fractures.
- A new vertebral compression fracture would indicate treatment failure or an underlying progression of osteoporosis, not a direct complication of the medication if it is working effectively.
*Interstitial nephritis*
- **Interstitial nephritis** is an inflammatory kidney condition often associated with drugs like **NSAIDs**, **antibiotics (e.g., penicillins, sulfonamides)**, and **diuretics**.
- It is not a characteristic side effect of bisphosphonates or other anti-resorptive agents used for osteoporosis.
*Agranulocytosis*
- Agranulocytosis is a severe reduction in **granulocytes (a type of white blood cell)**, typically associated with drugs like **propylthiouracil**, **methimazole**, **clozapine**, and certain **NSAIDs**.
- Medications that induce osteoclast apoptosis for osteoporosis do not commonly cause agranulocytosis.
Question 336: A 43-year-old man comes to the physician because of anxiety, difficulty focusing on tasks, and a 4.6-kg (10-lb) weight loss over the past 4 weeks. He is diaphoretic. His pulse is 100/min, respirations are 18/min, and blood pressure is 150/78 mm Hg. Physical examination shows warm, moist skin, goiter, and a resting tremor of both hands. Laboratory studies show a thyroxine (T4) concentration of 30 μg/dL and a thyroid-stimulating hormone concentration of 0.1 μU/mL. The patient is started on methimazole and atenolol. The latter agent predominantly affects which of the following?
A. Atrioventricular node activity (Correct Answer)
B. His-Purkinje conduction
C. Vagal tone
D. Phase 0 depolarization slope of the cardiac action potential
E. Effective refractory period of the cardiac action potential
Explanation: ***Atrioventricular node activity***
- Atenolol is a **beta-1 selective adrenergic blocker** used to manage hyperthyroidism symptoms.
- It primarily acts on the **AV node** to slow conduction and decrease heart rate, effectively controlling tachycardia and palpitations.
*His-Purkinje conduction*
- Conduction through the **His-Purkinje system** is not significantly affected by beta-blockers like atenolol.
- This system primarily dictates the rapid spread of electrical impulses through the ventricles.
*Vagal tone*
- Atenolol works by **blocking adrenergic receptors**, not by directly influencing the parasympathetic nervous system or vagal tone.
- Increased vagal tone would slow heart rate, but this is a separate mechanism.
*Phase 0 depolarization slope of the cardiac action potential*
- This phase is mediated by **fast sodium channels** in ventricular myocytes and Purkinje fibers.
- Beta-blockers primarily affect the **calcium-dependent action potentials** in the SA and AV nodes, not the fast sodium channels in ventricular tissue.
*Effective refractory period of the cardiac action potential*
- While beta-blockers can indirectly influence refractory periods by slowing heart rate, their primary direct effect is not on the **effective refractory period**.
- Medications that block potassium channels or sodium channels more directly impact the effective refractory period.
Question 337: A 53-year-old woman comes to the physician because of increasing shortness of breath on exertion for 5 months. She reports that she can not climb more than 2 flights of stairs and she is no longer able to run her errands as usual. One year ago, she was diagnosed with triple-negative breast cancer. She underwent a right-sided modified radical mastectomy and adjuvant chemotherapy. Cardiac examination shows a laterally displaced point of maximal impulse. Coarse inspiratory crackles are heard in both lower lung fields. Echocardiography shows a left ventricular ejection fraction of 30%. The physician informs the patient that her symptoms are most likely due to an adverse effect of her chemotherapy. The drug most likely responsible for the patient's current symptoms belongs to which of the following groups of agents?
A. Antimetabolites
B. Monoclonal antibodies
C. Alkylating agents
D. Topoisomerase I inhibitors
E. Anthracyclines (Correct Answer)
Explanation: ***Anthracyclines***
- The patient's presentation of **dilated cardiomyopathy** (shortness of breath, laterally displaced PMI, coarse crackles, reduced ejection fraction) following chemotherapy for breast cancer is characteristic of **anthracycline-induced cardiotoxicity**.
- **Anthracyclines** such as doxorubicin and epirubicin are known to cause **dose-dependent cardiotoxicity**, leading to irreversible myocardial damage and heart failure.
*Antimetabolites*
- **Antimetabolites** (e.g., methotrexate, 5-fluorouracil) primarily interfere with DNA synthesis and repair.
- While they can have side effects like myelosuppression and mucositis, **significant cardiotoxicity** leading to dilated cardiomyopathy is not their primary or most common adverse effect.
*Monoclonal antibodies*
- Some **monoclonal antibodies**, particularly trastuzumab (Herceptin), used in HER2-positive breast cancer, can cause cardiotoxicity, but it is typically **reversible** and not seen with triple-negative breast cancer unless used in combination with anthracyclines.
- The type of cardiomyopathy with trastuzumab is usually **reversible cardiac dysfunction** rather than irreversible dilated cardiomyopathy.
*Alkylating agents*
- **Alkylating agents** (e.g., cyclophosphamide, cisplatin) primarily damage DNA, leading to cell death.
- While they can cause various side effects, **dilated cardiomyopathy** is not a hallmark or common cardiotoxic effect, unlike anthracyclines, though high-dose cyclophosphamide can cause acute pericarditis or myocarditis.
*Topoisomerase I inhibitors*
- **Topoisomerase I inhibitors** (e.g., irinotecan, topotecan) typically cause gastrointestinal side effects (diarrhea), myelosuppression, and fatigue.
- **Cardiotoxicity** leading to dilated cardiomyopathy is not a prominent or common side effect associated with this class of drugs.
Question 338: A 68-year-old man with type 2 diabetes mellitus comes to the physician because of a 5-month history of episodic palpitations, dizziness, and fatigue. His pulse is 134/min and irregularly irregular, and his blood pressure is 165/92 mm Hg. An ECG shows a narrow complex tachycardia with absent P waves. He is prescribed a drug that decreases the long-term risk of thromboembolic complications by inhibiting the extrinsic pathway of the coagulation cascade. The expected beneficial effect of this drug is most likely due to which of the following actions?
A. Inhibit the reduction of vitamin K (Correct Answer)
B. Activate gamma-glutamyl carboxylase
C. Inhibit the phosphorylation of glutamate on the factor II precursor
D. Activate factor VII calcium-binding sites
E. Inhibit the absorption of vitamin K
Explanation: ***Inhibit the reduction of vitamin K***
- The patient's symptoms and ECG findings (irregularly irregular pulse, absent P waves, narrow complex tachycardia) are consistent with **atrial fibrillation**, which carries a high risk of **thromboembolic complications**.
- The drug described, acting on the **extrinsic pathway** and reducing thromboembolic risk, is most likely **warfarin**, a **vitamin K antagonist** that inhibits the reduction (regeneration) of vitamin K, thus impairing the synthesis of coagulation factors II, VII, IX, and X.
*Activate gamma-glutamyl carboxylase*
- **Gamma-glutamyl carboxylase** is an enzyme that requires reduced vitamin K as a cofactor.
- Warfarin's action is to **inhibit** the enzyme that *reduces* vitamin K, thereby *reducing* the activity of gamma-glutamyl carboxylase, not activating it.
*Inhibit the phosphorylation of glutamate on the factor II precursor*
- The modification of glutamate residues on coagulation factors is through **gamma-carboxylation**, not phosphorylation.
- Warfarin inhibits the **gamma-carboxylation** of factors II, VII, IX, and X, not their phosphorylation.
*Activate factor VII calcium-binding sites*
- Factor VII, like other vitamin K-dependent factors, requires **gamma-carboxylation** for calcium binding, which is essential for its activation and function.
- Warfarin **inhibits** this carboxylation, thereby impairing calcium binding and the activation of these factors, rather than activating their calcium-binding sites.
*Inhibit the absorption of vitamin K*
- While vitamin K absorption can be affected by certain conditions or drugs (e.g., malabsorption syndromes, broad-spectrum antibiotics), warfarin's primary mechanism of action is **post-absorption**, targeting the **epoxide reductase enzyme** involved in vitamin K recycling, not its intestinal absorption.
Question 339: An 11-year-old boy is brought to the physician by his mother because of a pruritic generalized rash for 2 days. He returned from a 3-day outdoor summer camp 1 week ago. During his time there, one child was sent home after being diagnosed with measles. The patient was diagnosed with a seizure disorder 6 weeks ago and he has asthma. Current medications include carbamazepine and an albuterol inhaler. His immunization records are unavailable. His temperature is 38.4°C (101.1°F), pulse is 88/min, and blood pressure is 102/60 mm Hg. Examination shows facial edema and a diffuse rash over the face, trunk, and extremities. There is cervical and inguinal lymphadenopathy. The remainder of the examination shows no abnormalities. Which of the following is the most appropriate next step in management?
A. Perform rapid plasma reagin test
B. Heterophile antibody test
C. Discontinue carbamazepine (Correct Answer)
D. Perform measles serology
E. Administer penicillin therapy
Explanation: ***Discontinue carbamazepine***
- The patient's symptoms (pruritic generalized rash, facial edema, fever, and lymphadenopathy) developing after starting carbamazepine are highly suggestive of **drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome**, a severe adverse drug reaction.
- The first and most critical step in managing **DRESS syndrome** is to immediately **discontinue the offending medication**, which in this case is carbamazepine.
*Perform rapid plasma reagin test*
- A **rapid plasma reagin (RPR) test** is used to screen for **syphilis**, which typically presents with a different rash morphology (e.g., maculopapular rash on palms and soles in secondary syphilis) and is less likely given the clear temporal association with a new medication.
- The patient's symptoms are not consistent with the typical presentation of syphilis, and the priority should be addressing the suspected drug reaction.
*Heterophile antibody test*
- A **heterophile antibody test** is used to diagnose **infectious mononucleosis**, which can cause fever, rash, and lymphadenopathy. However, the facial edema is less typical, and the clear link to a new medication makes DRESS syndrome a more probable diagnosis.
- While infectious mononucleosis can trigger rash, the combination of **facial edema** and the temporal relationship with carbamazepine initiation points more strongly to a drug-induced reaction rather than a primary infection.
*Perform measles serology*
- Although there was a measles case at the summer camp, the rash associated with **measles** is typically maculopapular, starts on the face, and spreads downward, often accompanied by **Koplik spots** and cough/coryza/conjunctivitis (**the 3 Cs**).
- The presence of **facial edema** and the timing relative to carbamazepine initiation make measles less likely as the primary diagnosis requiring immediate action.
*Administer penicillin therapy*
- **Penicillin therapy** is indicated for bacterial infections, particularly streptococcal infections or syphilis (as mentioned with RPR).
- The patient's presentation is more consistent with a **drug-induced hypersensitivity reaction** rather than a bacterial infection, making empirical antibiotic therapy inappropriate as the initial management step.
Question 340: A 35-year-old woman is admitted to the medical unit for worsening renal failure. Prior to admission, she was seen by her rheumatologist for a follow-up visit and was found to have significant proteinuria and hematuria on urinalysis and an elevated serum creatinine. She reports feeling ill and has noticed blood in her urine. She was diagnosed with systemic lupus erythematosus at the age of 22, and she is currently being treated with ibuprofen for joint pain and prednisone for acute flare-ups. Her blood pressure is 165/105 mmHg. Laboratory testing is remarkable for hypocomplementemia and an elevated anti-DNA antibody. A renal biopsy is performed, which demonstrates 65% glomerular involvement along with the affected glomeruli demonstrating endocapillary and extracapillary glomerulonephritis. In addition to glucocorticoid therapy, the medical team will add mycophenolate mofetil to her treatment regimen. Which of the following is the mechanism of action of mycophenolate mofetil?
A. Interleukin-2 receptor complex inhibitor
B. Inosine monophosphate dehydrogenase inhibitor (Correct Answer)
C. mTOR inhibitor via FKBP binding
D. Calcineurin inhibitor via cyclophilin binding
E. T-cell proliferation inhibitor
Explanation: ***Inosine monophosphate dehydrogenase inhibitor***
- **Mycophenolate mofetil** (MMF) is a prodrug that inhibits **inosine monophosphate dehydrogenase (IMPDH)**, an enzyme essential for *de novo* purine synthesis.
- This inhibition selectively blocks the proliferation of **T and B lymphocytes**, which are highly dependent on the *de novo* pathway for purine synthesis, thus suppressing the immune response in conditions like lupus nephritis.
*Interleukin-2 receptor complex inhibitor*
- This mechanism describes drugs like **basiliximab** and **daclizumab**, which are monoclonal antibodies that block the **IL-2 receptor** on T cells, preventing their activation and proliferation.
- These agents are primarily used in **transplantation** to prevent acute rejection, not typically for lupus nephritis.
*mTOR inhibitor via FKBP binding*
- This mechanism belongs to drugs like **sirolimus** (rapamycin) and everolimus, which bind to **FK-binding protein (FKBP)** and then inhibit **mammalian target of rapamycin (mTOR)**.
- While these drugs have immunosuppressive properties and are used in transplantation, they are not the primary mechanism of action for mycophenolate mofetil.
*Calcineurin inhibitor via cyclophilin binding*
- This mechanism describes drugs like **cyclosporine**, which binds to **cyclophilin** and then inhibits **calcineurin**, preventing the dephosphorylation of NFAT (nuclear factor of activated T-cells) and subsequent IL-2 transcription.
- **Tacrolimus** also acts as a calcineurin inhibitor but binds to FKBP. These drugs are used in transplantation and some autoimmune diseases but are not how MMF works.
*T-cell proliferation inhibitor*
- While MMF *does* inhibit T-cell proliferation, this description is a general outcome of many immunosuppressants and not its specific molecular mechanism of action.
- Many drugs can inhibit T-cell proliferation through different pathways, so a more precise description of MMF's action is its inhibition of **IMPDH**.
