Contraception in women with epilepsy: pharmacokinetic interactions, contraceptive options, and management

Contraceptive counseling is a critical component of the management of the female patient with epilepsy because of the increased risk of pregnancy associated with epilepsy and the multitude of interactions between antiepileptic drugs (AEDs) and hormonal contraception. Steroid hormones and many of the AEDs are substrates for the cytochrome P450 enzyme system, in particular, the 3A4 isoenzyme. As a result, concomitant use of hormonal contraceptives and AEDs may pose a risk for unexpected pregnancy, seizures, and drug-related adverse effects. The risk of combined oral contraceptive (COC) failure is slightly increased in the presence of cytochrome P450 3A4 enzyme-inducing AEDs. Several AEDs induce the production of sex hormone binding globulin (SHBG) to which the progestins are tightly bound, resulting in lower concentrations of free progestin that may also lead to COC failure. There is no increase in the risk of COC failure in women taking nonenzyme-inducing AEDs. Oral contraceptives significantly increase the metabolism of lamotrigine, posing a risk of seizures when hormonal agents are initiated and/or toxicity during pill-free weeks. There is no evidence that COCs increase seizures in women with epilepsy. While higher dose COCs are one contraceptive option for women on enzyme-inducing AEDs, a variety of other options are available. Injectable contraception (depot medroxyprogesterone acetate) appears effective with AED use, but the potential for bone mineral density loss is a concern. Intrauterine devices (IUDs) and barrier methods do not rely on hormonal components for contraceptive efficacy, and are therefore appropriate to recommend for use in women using enzyme-inducing medications. This chapter reviews the evidence regarding the pharmacokinetic interaction between AEDs and oral contraceptive hormones, the known or potential interactions with alternative contraceptive methods, and provides practical advice for management of contraceptive needs in reproductive-age women.