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
Which is Cytochrome P450 inhibitor? 
Select and explain. 
A. Ketoconazole, B. Rifampicin, C. Phenytoin, D. INH
A: Ketoconazole
Answer: A: Ketoconazole 
Explanation: Impoant microsomal enzyme inhibitors are: Valproate Ketoconazole Cimetidine Ciprofloxacin Erythromycin Isoniazid Ref: K.D.T 6th Ed Page 27,28.