Efficacy and tolerability of adjunctive therapy with zonisamide in childhood intractable epilepsy

Purpose: This study investigated the efficacy and safety of zonisamide (ZNS) adjunctive therapy in children with intractable epilepsy to existing antiepileptic drugs (AEDs). Methods: A clinical retrospective study was performed from 2003 to 2005 at two tertiary epilepsy centers. We reviewed the data from 163 children (107 boys and 56 girls) who experienced more than four seizures per month, whose seizures were intractable to an initial 2 or more AEDs, and could be followed up for at least 6 months after ZNS adjunctive therapy initiation. Efficacy was estimated by seizure reduction rate according to seizure types including infantile spasms, and adverse events were also measured. Results: Seventy-nine patients (48.5%) out of 163 patients experienced a reduction in seizure frequency of more than 50%, and 25 patients (15.3%) became seizure-free. The rate of seizure reduction greater than 50% in children with partial seizures was 40.5% (17/42) and in children with generalized seizures was 51.2% (62/121). Of 36 patients who manifested mainly myoclonic seizures, 20 patients (55.6%) showed a seizure reduction of more than 50% and 9 patients (25.0%) were seizure-free. Mean maintenance dosage of drug was 8.2 mg/kg/day (range 5.0-16.0 mg/kg/day). Adverse events were documented in 15 children (9.2%), including somnolence (8 patients), fatigue, and anorexia, but all were transient and successfully managed. One patient discontinued ZNS therapy due to acute pancreatitis. Conclusion: ZNS adjunctive therapy is an effective and safe treatment in various childhood intractable epilepsy.