This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Anticoagulant effect of warfarin is increased by all of the following drugs, EXCEPT: \nSelect and explain. \nA. Cimetidine, B. Phytonadione, C. Amiodarone, D. Phenylbutazone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Phytonadione is a vitamin K preparation and is used to control bleeding caused by warfarin. The anticoagulant effects of warfarin is increased by drugs that inhibits its metabolic clearance either through stereoselective or non selective pathways. Examples of such drugs are amiodarone, phenylbutazone, sulfinpyrazone, disulfiram, metronidazole, trimethoprim sulfamethoxazole, cimetidine, omeprazole, clofibrate, anabolic steroids. Drugs which increase the metabolic clearance of warfarin are: Barbiturates Rifampicin Griseofulvin Carbamazepine Ref: Thrombosis and Hemorrhage edited by Joseph Loscalzo, page 946.', 'role': 'assistant'}]