Randomized, Controlled Clinical Trial of Zonisamide as Adjunctive Treatment for Refractory Partial Seizures


Address correspondence and reprint requests to Dr. J.C. Sackellares at Department of Neuroscience, University of Florida Health Science Center, P.O. Box 100244, Gainesville, FL 32610-0244, U.S.A. E-mail: sackellares@epilepsy.health.ufl.edu


Summary: Purpose: This study was designed to evaluate efficacy and safety of zonisamide (ZNS) as adjunctive treatment for patients with refractory partial seizures.

Methods: This randomized, double-blind, placebo-controlled study was conducted at four epilepsy treatment centers. It included a baseline phase (8 to 12 weeks) and a double-blind treatment phase (12 weeks). Initially, patients randomized to ZNS treatment were given a 7-mg/kg/d dosage. When investigators found that adverse effects could be reduced by gradually introducing ZNS, patients were allowed to begin treatment at lower doses (100 mg or ∼1.5 mg/kg/d) titrated over several weeks to a maximum of 400 to 600 mg/d. Primary and secondary efficacy measures were the median percentage reduction from baseline in seizure frequency and the proportion of patients achieving a ≥50% reduction from baseline (responder rate). Patient and physician global assessments also served as indicators of efficacy. Safety was assessed primarily by treatment-emergent adverse events.

Results: ZNS-treated patients had a 28.9% reduction in seizure frequency, which differed significantly from the 4.7% increase in placebo-treated patients. The responder rate for ZNS-treated patients was 26.9%, compared with 16.2% for placebo-treated patients. At study's end, 66.2% of ZNS-treated patients and 12.3% of placebo-treated patients considered their condition improved; similarly, physicians assessed 63.6% of ZNS-treated patients and 10.8% of placebo-treated patients as improved. The most frequently reported adverse events with ZNS treatment included somnolence, irritability, dizziness, nausea, and fatigue.

Conclusions: As adjunctive treatment, ZNS was generally well tolerated and significantly improved seizure control among patients with refractory partial seizures.