Abstracts

It has been shown that combined oral contraceptives reduce lamotrigine (LTG) serum concentrations by more than 50% (1). We wanted to investigate whether this finding is true only for ethinylestradiol (EE) containing preparations or also for other hormonal contraceptive methods. We collected data from a prospective series of routine measurements of LTG serum concentration in young women. LTG concentration-to-dose ratios (CDR) of patients using any form of hormonal contraception were compared with CDR of patients not using hormonal contraception. An interim analysis of the data collected so far confirms that contraceptive drugs containing EE reduce LTG CDR by 50%. This effect was observed for the combined oral contraceptive pill as well as for the vaginal contraceptive ring. The CDR of patients using gestagen-only contraception (subdermal implant and intrauterine device) did not differ from controls. In one patient first treated with an EE-containing oral contraceptive, the CDR soon rose to values in the control range after the contraceptive was discontinued. CDR remained stable over several weeks after the introduction of a gestagen-containing implant. EE, but not gestagens, decreases LTG serum concentration. This effect is independent of the administration form and is an important fact to bear in mind when counselling women with epilepsy in child-bearing age.
References
1. Sabers A, öhman I, Christensen J, Tomson T: Oral contraceptives reduce lamotrigine plasma levels. Neurology 2003;61:570-571