Coagulation Disorders USMLE Step 1 Practice Question
A 72-year-old man with a history of atrial fibrillation has been taking warfarin for 18 months with a stable INR of 2.8–3.2. He presents to the emergency department with gross hematuria, spontaneous epistaxis, and gingival bleeding that began yesterday. Vital signs are stable (BP 128/76 mmHg, HR 92/min, RR 16/min). Laboratory studies show INR 9.4, PT 68 seconds, aPTT 42 seconds, platelets 245,000/μL, and hemoglobin 9.8 g/dL (baseline 13.2 g/dL three weeks ago). He denies recent trauma, abdominal pain, melena, or change in dietary vitamin K intake. Three days ago, he started a new antibiotic for a urinary tract infection. Which of the following medications most likely explains his supratherapeutic INR and bleeding manifestations?
Answer choices
- ARifampin
- BCarbamazepine
- CTrimethoprim-sulfamethoxazoleCorrect answer
- DPhenytoin
- EFluconazole
- FAmoxicillin-clavulanate
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