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
Oral contraceptive failure may be seen with ? 
Select and explain. 
A. Rifampicin, B. Cimetidine, C. Propranolol, D. Ethambutol
A: Rifampicin
Answer: A: Rifampicin 
Explanation: Ans. is 'a' i.e., Rifampicin o Contraceptive failure may occur if the following drugs are given concurrently : (a) Enzyme inducer --> Enhances the metabolism of estrogen & progesterone. Phenytoin 3. Carbamazepine 5. Primidone Phenobarbitone 4. Rifampicin 6. Griseofulvin (b) Suppression of intestinal microflora enterohepatic circulation. 1. Tetracyclines 2. Ampicillin