Teratogenic potential of the newer antiepileptic drugs: what is known and how should this influence prescribing?

The treatment of women of childbearing age who have epilepsy raises many questions because of the interactions between epilepsy, antiepileptic therapy and different aspects of reproductive life. Menstrual cycle disorders and reduced fertility have been partially ascribed to antiepileptic drugs (AEDs). Furthermore, most AEDs induce the cytochrome P450 (CYP) enzymatic system, altering the metabolism of sex hormones and contributing to the failure of oral contraceptives. Pregnancy represents, in this context, the most critical period because of the well known teratogenic potential of all established AEDs. For most of these drugs no specific patterns of malformations have been identified, although during the past few decades basic knowledge has been acquired, particularly concerning the mechanisms of AED-induced teratogenesis and related risk factors. These issues form the basis of the current guidelines for the management of epilepsy in pregnant women. In the past decade, several new AEDs have been introduced into clinical practice. For a number of reasons, these drugs appear to be more favourable than the older ones as treatments for epilepsy in women of childbearing age. They possess a good pharmacokinetic profile that makes them more stable during pregnancy, and they have a low potential for interaction with other drugs. They are also less likely than the older AEDs to be metabolised to compounds that are teratogenic. Furthermore, most of them do not possess antifolate properties. With the exception of topiramate and vigabatrin, the newer AEDs do not appear to be teratogenic in animals when administered in subtoxic doses. However, animal teratology may not be a reliable predictor of human teratogenicity, and there is a significant lack of information regarding the teratogenic profile of these newer agents in humans. Because clinical experience with these agents is limited, it is advisable to avoid exposure of the embryo to these drugs when pregnancy is planned. The establishment of pregnancy registries could allow for the rapid collection of data related to the administration of new AEDs in pregnancy and the outcomes of such exposure.