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 except- \nSelect and explain. \nA. Cimetidine, B. Phytonadione, C. Amiodarone, D. Phenylbutazone', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Phytonadione o Warfarin shows a number of drug interactions and requires dose adjustment :? 1) Enzyme inducers (phenobarbitone, rifampicin, phenytoin, griseofulvin etc) and oral contraceptives (increase clotting factors) decrease the effect and hence require increase in dose of warfarin. 2) Drugs that increase the effect of warfarin and require dose reduction are enzyme inhibitors (cimetidine, erythromycin, cotrimoxazole, disulfiram, isoniazid, metronidazole, azoles, allopurinol), cephalosporins (cefamendole, cefoperazone, moxalactam), phenylbutazone, amiodarone, sulfinpyrazone, acute alcohol intake, loop diuretics and valproate.", 'role': 'assistant'}]