The occurrence of interactions between enzyme-inducing
AEDs and combined oral contraceptives (OCs) became
obvious some years after the introduction of OC preparations
[3]. The main consequence of these interactions is
the risk of contraceptive failure and unwanted pregnancy,
and high-estrogen OCs are often prescribed to minimize
this risk in women on enzyme-inducing AEDs. High-dose
estrogen OCs and high-dose hormonal replacement therapy
(HRT), however, might increase the risk of thromboembolic
adverse effects as well as breast cancer [4,5]. The
extent of enzyme induction is correlated to the dose of
the AED but it is difficult to quantify, as genetic and environmental
factors also influence expression of hepatic isoenzymes.