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
Which of the following drugs is an inhibitor of cytochrome p450 enzymes? 
Select and explain. 
A. Ketoconazole, B. Rifampicin, C. Phenytoin, D. Phenobarbitone
A: Ketoconazole
Answer: A: Ketoconazole 
Explanation: Ans. (A) Ketoconazole(Ref: KDT 8th/e p30)Ketoconazole is a powerful microsomal enzyme inhibitor whereas rifampicin, phenobarbitone and phenytoin are enzyme inducers.