This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Pharmacology, Subject name: Pharmacology
[{'content': 'Which of the following drugs is an inhibitor of cytochrome p450 enzymes? \nSelect and explain. \nA. Ketoconazole, B. Rifampicin, C. Phenytoin, D. Phenobarbitone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (A) Ketoconazole(Ref: KDT 8th/e p30)Ketoconazole is a powerful microsomal enzyme inhibitor whereas rifampicin, phenobarbitone and phenytoin are enzyme inducers.', 'role': 'assistant'}]