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': '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: - Cytochrome p450 enzymes are microsomal enzymes (present on smooth endoplasmic reticulum).\n- Of the given options, only Ketoconazole is a microsomal enzyme inhibitor. Rest all are enzyme inducers.', 'role': 'assistant'}]