This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraception, Subject name: Gynaecology & Obstetrics
[{'content': 'Oral contraceptive Pill (OCP) failure is seen with all except: \nSelect and explain. \nA. Rifampicin, B. Phenobarbitone, C. Valproate, D. Phenytoin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Drugs leading to OCP failure are: Rifampicin Tetracyclines Phenytoin Phenobarbitone Antifungals Cephalosporin Ritonavir for HIV (interferes with absorptionn of OCP) Ref: online resources (ncb.nlm.nih.gov)', 'role': 'assistant'}]