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': 'The anticoagulant effect of warfarin is increased by all of the following EXCEPT: \nSelect and explain. \nA. Cimetidine, B. Phytonadione, C. Amiodarone, D. Phenylbutazone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Vitamin K1\xa0(phytonadione) is the antidote of warfarin. It decreases the effect of oral anticoagulants.', 'role': 'assistant'}]