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Theoretically yes. Commonly used liver enzyme inducers (e.g., rifampin/rifampicin and most anticonvulsants) may reduce the efficacy of CICs. Use of other contraceptives should be encouraged for women who are on long term use of:
- rifampin/rifampicin (an antibiotic), or
- anticonvulsants, such as phenytoin, phenobarbital, or carbamazepine.
Other antibiotics should not affect the efficacy of CICs.
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Little is known about the effects of other drugs on the effectiveness of CICs. However, based on combined oral contraceptive (COC) data, anticonvulsants, such as phenytoin, phenobarbitol and carbamazepine, the antibiotic rifampin/rifampicin, and possibly the antifungal agent griseofulvin will require use of a back-up method to compensate for hepatic microsomal enzyme induction. Hepatic micro-enzyme induction by rifampin/rifampicin lasts for 4 weeks for short-term use and for 8 weeks for long-term use. Although anecdotal reports of failure to prevent pregnancy in COC users exist for other antibiotics, epidemiological evidence suggests that most antibiotics (except rifampin/rifampicin and griseofulvin) do not require use of a back-up method.
- Orme M, Back DJ. Oral contraceptive steroids - pharmacological issues of interest to the prescribing physician. Advances in Contraception 1991;7:325-31.
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