<prompt> Oral contraceptive failure may be seen with ?RifampicinCimetidinePropranololEthambutol  <response>: 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 