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 does not effect metabolism of oral contraceptive pill ? 
Select and explain. 
A. Phenytoin, B. Gresiofulvin, C. Primidone, D. Penicillin
D: Penicillin
Answer: D: Penicillin 
Explanation: Ans. is d i.e., Penicillin Contraceptive failure may occur if the following drugs are given concurrently : a) Enzyme inducer - Enhances the metabolism of estrogen & progesterone. Phenytoin Carbamazepine Primidone Phenobarbitone Rifampicin Griseofulvin b) Suppression of intestinal microflora - enterohepatic circulation. Tetracyclines Ampicillin