Open label extension study following a double-blind, randomized, placebo-controlled, multicenter study to assess the efficacy and safety of adjunctive zonisamide in primary generalized tonic-clonic seizures.

This study is an Open label extension study following a double-blind, randomized, placebo-controlled, multicenter study to assess the efficacy and safety of adjunctive zonisamide in primary generalized tonic-clonic seizures. Zonisamide is an investigational drug. RESEARCH OBJECTIVES To assess the long-term safety and efficacy of zonisamide in subjects with primary generalized tonic-clonic seizures. STUDY DESIGN Subjects who completed Visit 7 of the double blind study (E2090-E044-315) will be invited to enter into this extension study. After provision of informed consent at this visit, the study will start with a double-blind Titration Period (to avoid unblinding of study E2090-E044-315). Subjects treated with zonisamide in study E2090-E044-315 will continue on the same dose of zonisamide while they are being started with placebo. Subjects treated with placebo in study E2090-E044-315 will continue to take placebo and additionally be uptitrated with zonisamide up to the dose level that subjects were treated with at the end of study E2090-E044-315 (up to a maximum of 400 mg or 350 mg (6 mg/kg) if the subject is less than 12 years of age). For those subjects in the placebo group, dosing with zonisamide will start with a dose of 1 mg/kg (subjects < 12 years) or 50 mg (subjects = 12 years). The dose of zonisamide is up titrated in the same schedule as in study E2090-E044-315. The Titration Period will last four to seven weeks. Subjects who completed the double blind study on a maximum tolerated dose of 200 mg (or 4 mg/kg for subjects <12 years) will complete titration more quickly than other subjects i.e within 3 weeks, but will be maintained on the Week 3 dose for another week during the Titration Period in order to maintain the blind, before entering the open label Maintenance Period. In subjects who do not tolerate this titration, both the blinded maintenance dose from study E2090-E044-315 and the transition titration dose introduced in E2090-E044-316 will be downtitrated to 100 mg (if adult or child < 12 years and weight >28 kg) or 50 mg (if child < 12 years and weight 20-28 kg). When this dose is reached, open-label zonisamide will be started at the age/weight-appropriate starting dose, if this is decided to be in the best interest of the subject by the investigator. After this period subjects who completed the uptitration will be taking the maintenance dose of zonisamide so the study will become in effect open label and a switch is made to open-label maintenance medication. The dose of open-label zonisamide through the remainder of the study will be flexible at the discretion of the investigator and based on tolerability and efficacy. Trial medication will be taken once daily in the evening throughout the study.