Zonisamide Monotherapy in Newly Diagnosed Infantile Spasms

PURPOSE: We determined the short-term efficacy of zonisamide (ZNS) monotherapy in newly diagnosed patients with infantile spasms (IS). METHODS: Eleven hospitals participated in this open, prospective trial. ZNS 3-10 mg/kg/day was administered as the second-choice drug to 11 newly diagnosed patients with IS (cryptogenic 3, symptomatic 8) who failed to respond to high-dose vitamin B6. RESULTS: Four infants with symptomatic IS had cessation of spasms and disappearance of the hypsarrhythmia. In these responders, the spasms ceased after a few days (1-5 days) of treatment at a dose of ZNS 4-5 mg/kg/day which produced plasma ZNS concentrations ranging from 5.2 to 16.3 microg/ml (mean 9.8 microg/ml). There were two relapses (50%) 4-6 weeks after cessation of seizures, however. Relapse was predicted by effects of ZNS on EEG; the 2 infants in whom an abnormal EEG persisted had relapses, whereas the 2 whose EEG normalized remained seizure-free (follow-up 20 and 26 months). No adverse reactions were noted. CONCLUSIONS: ZNS may be effective in the initial treatment of selected patients with IS.