4. DRUG INTERACTIONS
The effectiveness of progestin-only pills is reduced by hepatic enzyme-inducing drugs such as the anticonvulsants, phenytoin, carbamazepine; barbiturates; the antituberculosis drug rifampin; protease inhibitors; and herbal preparations containing St. John's Wort (hypericum perforatum). This could result in unintended pregnancy or breakthrough bleeding. There are anecdotal reports of reduced efficacy of combination oral contraceptives when used concomitantly with broad-spectrum antibiotics. No significant interaction has been found with progestin-only oral contraceptives and broad-spectrum antibiotics.
During concomitant use of OVRETTE and substances that may affect its efficacy, it is recommended that a nonhormonal back-up method of contraception be used in addition to the regular intake of OVRETTE. Use of a nonhormonal back-up method is advisable after discontinuation of substances that have led to induction of hepatic microsomal enzymes. It may take several weeks until enzyme induction has subsided, depending on dosage, duration of use, and rate of elimination of the inducing substance. For women receiving long-term therapy with hepatic enzyme inducers, another method of contraception should be considered.
Substances that reduce gastrointestinal transit time may affect contraceptive efficacy.
The product information of concomitant medications/substances should be consulted to identify potential interactions.