Preliminary report on teratogenic effects of zonisamide in the offspring of treated women with epilepsy

Purpose: We wished to assess the risk of teratogenicity of zonisamide (ZNS) in humans. Methods: Pregnant epileptic women treated with ZNS and their offspring were prospectively monitored from June 1989 to December 1994. The outcome of pregnancy and status of neonates were examined based on the same standardized protocol. Results: Twenty-six offspring exposed to ZNS with or without other antiepileptic drugs (AEDs) were studied. Malformations were detected in 2 offspring (7.7%) exposed to ZNS polypharmacy. Anencephaly was detected in one case at 16 weeks of gestation (case 1, artificial abortion), and atrial septal defect was detected in another case at 37 weeks of gestation (case 2, delivery by cesarean section). Serum concentrations of ZNS during the first trimester of pregnancy were 6.1 mu g/ml in case 1 and 6.3 mu g/ml in case 2; in both cases, the levels were below the therapeutic concentration range of ZNS. Conclusions: Teratogenic effects of ZNS were not clearly defined from these results since malformations were detected in two polypharmacy cases but not in four monopharmacy cases. The present data do not indicate that the risk of ZNS teratogenicity is greater than that of other conventional AEDs. However, such risk cannot be neglected even at therapeutic dosages or concentrations of ZNS, especially in patients receiving polypharmacy.