Cardiovascular Drugs USMLE Step 1 Practice Question
A 70-year-old man with chronic atrial fibrillation on warfarin (INR stable at 2.5 for 3 weeks) is started on amiodarone for rate control. One week later, he presents with gross hematuria and petechiae. Vital signs: BP 128/76, HR 62, RR 16, Temp 37°C, SpO2 98%. Laboratory studies reveal INR 8.2 and hemoglobin 9.8 g/dL. Urinalysis shows blood without proteinuria. Which mechanism explains this serious drug interaction?
Answer choices
- AAmiodarone increases hepatic synthesis of clotting factors
- BAmiodarone inhibits CYP2C9, decreasing warfarin metabolismCorrect answer
- CAmiodarone inhibits CYP3A4, decreasing warfarin metabolism
- DAmiodarone increases warfarin clearance via renal excretion
- EAmiodarone displaces warfarin from plasma protein binding
- FAmiodarone inhibits vitamin K-dependent clotting factor synthesis in the liver
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