The purpose of this study is to assess the long-term safety and efficacy of zonisamide used as an adjunctive treatment in pediatric subjects treated with 1 or 2 other anti-epileptic drugs (AEDs).

Those subjects who completed the double-blind study (E2090-E044-312) will be invited to participate in this extension study. The study consists of two main parts: Transition Period (double-blind) and Open Label Period. The study will start with the Transition Period during which subjects already on zonisamide will continue on the same dose of zonisamide and those who were taking placebo will be up-titrated to an appropriate dose of zonisamide. After all subjects have completed the Transition Period, the study will become open-label with every subject on the study receiving zonisamide. The study medication will be taken once daily in the evening. For those subjects previously in the placebo group, dosing with zonisamide will start with a dose of approximately 1 mg/kg. In order that the blind is maintained from the previous study, these subjects will initially continue taking the same number of placebo capsules as they were taking in the Maintenance Period of the E2090-E044-312 study until the up- titration is completed. Those subjects previously in the zonisamide arm will continue on the same dose which they received during the Maintenance Period of the E2090-E044-312 study. In order that the blind is maintained, they will also take placebo capsules in order to mirror the up- titration dose regimen of the subjects previously randomized to receive placebo in the E2090-E044-312 study. All subjects will stop taking placebo capsules after the Transition Period is complete. The duration of the Transition Period depends on the dose the subject appeared to have received when completing the core study E2090-E044-312. For those who completed on 8 mg/kg, the Transition Period will last 7 weeks. For those on 6 mg/kg, the Transition Period will last 5 weeks. However, during the double-blind Transition Period, some subjects may experience adverse events (AEs). If this should occur, the subject may be down titrated to one level above the minimal dose. The overall duration of the study will be up to 59 weeks. The overall duration of the Transition Period may thus be as short as 2 weeks or prolonged to as many as 11 weeks.

The Open Label Period will continue for up to a maximum of 59 weeks (approximately 15 months).

At the end of the study, Eisai will continue to supply zonisamide as part of this open-label extension protocol until the marketing authorisation of zonisamide for this indication or further development in this indication is stopped. In countries where no marketing authorisation will be applied for, Eisai has a compassionate use policy which can be applied for, if required.

INCLUSION CRITERIA:

1. Subject has completed the double-blind study E2090-E044-312.
2. Parent/caregiver is willing to sign an informed consent where the subject is under the age of consent.
3. Subject is male or female aged 6 to 18 years who is willing to give informed (written or verbal) assent, if applicable. If mandated by local regulations, subjects of relevant age will be required to sign an appropriate informed consent.
4. Subject is in general good health as determined by medical history, physical exam and screening laboratory results.

EXCLUSION CRITERIA:

1. Subject has a body weight < 20 kg.
2. Subject has developed a history of renal calculi or renal insufficiency (creatinine level > 135 µmol/l (1.5 mg/dl).
3. Subject has a known diagnosis of human immunodeficiency virus (HIV) or hepatitis B or C.
4. Subject has a history of sensitivity to sulfonamide drugs or zonisamide and its excipients.
5. Female subject of 10 years of age or greater, or of child bearing potential (i.e. started menses) and is not taking or prepared to take a medically acceptable form of contraception (i.e. oral contraceptive pill, surgical sterilization, an implant or injected form of contraception, or intrauterine device), or who is not prepared to abstain from sexual activity for the duration of the study and for one month after the last administration of study medication. NOTE: Should a female subject become of child bearing potential during the study, they must be reconsented in order to given consent to undergo pregnancy testing and either confirm abstinence or receive a medically appropriate form of contraception.
6. Subject has a recent history of excessive alcohol use or drug abuse.
7. Subject has a history of suicide attempt.
8. Subject has a clinically significant organic disease.
9. Subject has a history of demonstrated non-compliance with treatment or subject or parent/legal guardian can be reasonably expected not to be compliant with study procedures or to complete the study.
10. Frequent need of rescue benzodiazepines (one or more times a month).
11. Concomitant use of acetazolamide, carbonic anhydrase inhibitors such as topiramate, furosemide and drugs with anticholinergic activity.
12. Concomitant use of felbamate or use of felbamate within 2 months prior to Visit 1 of the E2090-E044-312 study.

"Treatment-Emergent Adverse Events (TEAE) were collected, and includes all Adverse Events (AE) with a start date on or after Day 1 and within 15 Days of last dose, including AEs with missing start dates. Participants were followed for up to 61 weeks.

Treatment-emergent AEs were summarized by period (Transition, Open-label, Down-titration), treatment group,body system, and preferred term (PT).