Carbamazepine coadministration with an oral contraceptive

Abstract

To the Editors: We read with interest the article by Brodie et al. (2013) concerning the enzyme induction with antiepileptic drugs (AEDs) and their consequences. The paragraph “Reproductive Hormones, Sexual Function, and Oral Contraceptives in Women” illustrates the interaction of enzymeinducing AEDs on oral contraceptives underscored by the study of Davis et al. (2011). In their study they revealed a decrease of estrogen and levonorgestrel serum levels during intake of carbamazepine, compared to a control group and suggesting that carbamazepine interacts with both. The patients took a low dose oral contraception (20 lg ethinyl estradiol and 100 lg levonorgestrel). The size of the study was small (n = 10), although the results support previous findings. As an alternative to low-dose combined oral contraception this article recommends a higher dosage of the estrogen component, as high as 50 lg, although there is no proof of this therapy. There are some points that have to be considered when choosing a high dosage combined oral contraceptive: 1 50 lg of estrogen inhibits breakthrough bleeding but is still far below ovulation inhibition dosage (100 lg) (Schwenkhagen & Stodieck, 2008). The ovulation inhibition and other factors such as tube motility for the protection against pregnancy is given through progestins. 2 Side effects such as thromboembolism and myocardial infarction occur more frequently when the dosage of estrogen is increased (Lidegaard et al., 2009, 2012). Van Hylckama Vlieg et al. (2009) revealed an increase— with an estrogen dose of 30 lg as the reference category—from 0.8 (20 lg estrogen) to 1.9 (50 lg estrogen) for the thrombotic risk. Studies have to be continued to find pregnancy protection for women with epilepsy. The following approaches could help find a solution: 1 Combined oral contraception with certain progestins, which do not interact with AEDs, could be taken continuously without pill-free intervals (Schwenkhagen & Stodieck, 2008). 2 Nonhormonal contraception such as intrauterine copper devices should be considered. DISCLOSURE