A 58-year-old man visits your clinic for evaluation of fatigue and easy bruising over the past few weeks. He has a history of hypertension and atrial fibrillation and is on lisinopril for hypertension and warfarin for anticoagulation. He reports worsening heartburn and mentions using a medication from his wife’s medicine cabinet for relief. On examination, mild jaundice and scattered ecchymoses are noted. Laboratory tests reveal elevated liver enzymes, a high prothrombin time (PT), and an increased international normalized ratio (INR). Which of the following is the most likely medication he has been taking?
