Cardiovascular Drugs USMLE Step 1 Practice Question
A 58-year-old man presents with chest pain and dyspnea. Vital signs: BP 128/82 mmHg, HR 102/min, RR 18/min, temp 37.2°C, SpO2 98% on room air. He receives aspirin, clopidogrel, and unfractionated heparin for suspected acute coronary syndrome. Two hours later, aPTT is 95 seconds (normal 25-35 sec), troponin is elevated at 2.8 ng/mL, and ECG shows ST-segment depression. No bleeding noted. Which drug explains the prolonged aPTT?
Answer choices
- AAspirin acetylates platelet cyclooxygenase, directly inhibiting thrombin generation
- BAll three drugs synergistically inhibit factor II, V, VII, and X
- CHeparin directly degrades fibrinogen into fibrin degradation products
- DUnfractionated heparin inactivates thrombin and factor Xa by enhancing antithrombin III activityCorrect answer
- EClopidogrel irreversibly inhibits platelet ADP receptors, preventing factor activation
- FClopidogrel competitively inhibits factor IIa, directly prolonging the intrinsic coagulation cascade
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