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 is an enzyme inhibitor? 
Select and explain. 
A. Ketoconazole, B. Rifampicin, C. Tolbutamide, D. Phenobarbitone
A: Ketoconazole
Answer: A: Ketoconazole 
Explanation: Eg for enzyme inducers- phenytoin, phenobarbitone, carbamazepine, rifampin An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. eg for enzyme inhibitors: ketoconazole, grapefruit juice, ciprofloxacin, chloramphenicol Refer cha Pg.no 26. KD TRIPATHI SEVENTH EDITION