Objective: To describe a series of serum concentrations of zonisamide in a pregnant woman.
Case summary: A 30-year-old woman with primary generalized tonic-clonic seizures and myoclonic jerks was taking zonisamide 200 mg daily as her sole antiepileptic agent when she conceived. She continued on zonisamide throughout her pregnancy. The zonisamide concentrations ranged between 7.5 microg/mL and 17 microg/mL during pregnancy, with the exception of a 4.4-microg/mL concentration at 27 weeks postconception. Following this lower concentration, the zonisamide dose was increased to 300 mg/day at week 29. She had an uneventful pregnancy, with only occasional myoclonic jerks, and delivered at 41 weeks. At 42 weeks, while taking zonisamide 300 mg/day, her concentration was 20.8 microg/mL.
Discussion: A single report from Japan reviewed 26 cases of prenatal exposure to zonisamide. Twenty-two offspring were exposed to zonisamide monotherapy; 4 were exposed to polytherapy. During the first trimester, 2 pregnant women on zonisamide and at least one other antiepileptic medication had serum concentrations of 6.1 microg/mL and 6.2 microg/mL; 2 of the infants had teratogenic effects. Teratogenicity has also been reported in animals. There are no other published data regarding zonisamide concentrations during pregnancy.
Conclusions: The change in zonisamide serum concentrations in a pregnant woman suggests an increase in clearance at the end of the second trimester.