CONTRACEPTION BY NORPLANT SUBDERMAL CAPSULES IS NOT RELIABLE IN EPILEPTIC PATIENTS ON ANTICONVULSANT TREATMENT

The contraceptive efficacy of progestin-only contraception was studied in epileptic patients using NORPLANTR subdermal capsules. The effect of anticonvulsants of levonorgestrel plasma levels was determined. NORPLANTR subdermal capsules were inserted into nine epiletic women, and ten control women using no medication. Venous blood samples were taken at 0, 1, 3, 6, 9 and 12 months after insertion and the concentration of levonorgestrel was determined by radioimmunoassay. At 3 to 12 months, the overall mean concentration of plasma levonorgestrel was significantly lower in the six epileptics taking phenytoin alone or in combination with other anticonvulsants (203 .+-. 128 pg/ml, mean .+-. SD) than in the controls (325 .+-. 135 pg/ml, p < 0.01). After one year, nine of the control patients continued the use of NORPLANTR and no pregnancies occurred. Two of the nine epileptics became pregnant during contraception by NORPLANTR. They both used phenytoin and their plasma concentrations of levonorgestrel were low near the time of conception. Levonorgestrel released from the capsules had no apparent harmful effects on epilepsy and none of the patients reported an increase in seizure frequency. The results show that contraception by the progestin levonorgestrel is not reliable in epileptic patients using anticonvulsants known to induce metabolizing enzymes of the liver.