Implanon, the first long-term implantable contraceptive to win FDA approval and become available in the United States since 2000 when Wyeth stopped marketing Norplant, may not be effective in women taking antiepileptic drugs, said Dr. Andrew M. Kaunitz.
A single-rod contraceptive implant that is about the size of a matchstick, Implanon is highly effective for up to 3 years in women who do not take antiseizure medication.
In an interview, Dr. Kaunitz, professor and assistant chairman of the department of obstetrics and gynecology at the University of Florida Health Science Center, Jacksonville, said that because their contraceptive efficacy is associated with low serum progestin levels, “contraceptive implants and progestin-only OCs do not represent optimal contraceptives for women who take (or will soon initiate) anticonvulsants or other concomitant medications, which induce hepatic enzymes.” Dr. Kaunitz's department has conducted clinical trials for Organon.
The label includes a warning and precautions about Implanon and antiepileptic interactions and other drugs that are potent inducers of hepatic enzymes, because coadministration may substantially lower etono- gestrel levels and reduce the effectiveness of the contraceptive. The drugs include phenytoin, carbamazepine, felbamate, topiramate, and oxcarbazepine.
In trials, bleeding irregularities were frequent and were the most common reason for choosing to discontinue the contraceptive.
Implants and progestin-only OCs could induce hepatic enzymes in those taking anticonvulsants. DR. KAUNITZ