Changes in Contraceptive Effectiveness Associated with Co-Administration of Other Drugs
a. Anti-Infective Agents and Anticonvulsants
IMPLANON™ is not recommended for women who require chronic use of drugs that are potent inducers of hepatic enzymes because IMPLANON™ is likely to be less effective for these women.
Contraceptive effectiveness may be reduced when hormonal contraceptives are co- administered with some antibiotics, antifungals, anticonvulsants, and other drugs that increase the metabolism of contraceptive steroids. This could result in an unintended pregnancy or breakthrough bleeding. Examples include barbiturates, griseofulvin, rifampin, phenylbutazone, phenytoin, carbamazepine, felbamate, oxcarbazepine, topiramate, and modafinil. Patients should use an additional nonhormonal contraceptive method when taking medications that may decrease the efficacy of hormonal contraceptives.
b. Anti-HIV Protease Inhibitors
Several of the anti-HIV protease inhibitors have been studied with co-administration of combination oral contraceptives; significant changes (increase and decrease) in the mean area under the curve (AUC) of the estrogen and progestin have been noted in some cases. The efficacy and safety of combination oral contraceptive products may be affected with co-administration of anti-HIV protease inhibitors; it is unknown whether this applies to IMPLANON™. Healthcare providers should refer to the labeling of the individual anti-HIV protease inhibitors for further drug-drug interaction information.
c. Herbal Products
Herbal products containing St. John's Wort (Hypericum perforatum) may induce hepatic enzymes and p-glycoprotein transporter and may reduce the effectiveness of contraceptive steroids.