your 69 year-old patient who has been taking warfarin for chronic atrial fibrillation appears in your office looking pale and complaining of weakness. you check his blood pressure and find it much lower than during his three most recent clinic visits. he mentions having had a dark tarry stool for the past three days, and his lab test indicates a high protrombin time and low hematocrit. when questioned about his recent history he mentions taking otc cimetidine for an upset stomach for the past few days. the most likely explanation for your patient's symptoms is: a. cimetidine induction of warfarin metabolism b. cimetidine inhibition of warfarin metabolism c. cimetidine induced synthesis of clotting factors d. cimetidine interfering with warfarin absorption e. cimetidine reducing the anticoagulant effect of warfarin