Efficacy and Safety of an add-on Treatment With Zonisamide in Adults With Focal Epileptic Seizures With or Without Secondary Generalization

Inclusion criteria at screening: * Adult aged between 18 years and 74 years * Focal epileptic seizures with or without secondary generalization * Present treatment with one or two antiepileptic drugs (constant dosage during 8 weeks baseline phase prior to initiation of treatment with zonisamide). Stimulation of the vagus nerve is permitted and will not be counted as antiepileptic drug. * For women of childbearing potential (postmenopausal for more than 1 year): possible pregnancy during the study can be excluded (by hysterectomy, sterilization or simultaneous application of two recognized methods of contraception (no oral contraceptives only) * For male patients with partners of childbearing potential: a safe method of contraception is practiced during their study participation * Written consent to participate in the study Inclusion criteria for randomisation: * At least 6 focal or clonicotonic seizures documented completely in a seizure diary or the patient chart during the 8 prospective or retrospective weeks baseline phase. Exclusion criteria at screening: * Epileptic state during the past year * Non-epileptic fits * Generalized epilepsy * More than 4 weeks of seizure freedom during baseline phase * Concomitant progressive CNS disease including progressive myoclonus epilepsy * Concomitant treatment with vigabatrine and / or topiramate * Hepatic and/or renal insufficiency (creatine \> 2mg% or GPT \> 2 times ULN) * Body weight ≤ 40 kg * (History of) kidney stones; erythrocyturia, family history (in parents, children, brothers and sisters or grandparents) of kidney stones * (History of) drug and/or alcohol dependence * Active psychosis * Suicide attempt during the past 3 years * Pre-treatment with zonisamide * Known hypersensitivity to sulfonamides * concomitant treatment with neuroleptic drugs * pregnant or breast feeding woman * participation in another therapy study within 3 months prior to or during this study * blood donation planned during or within 4 weeks after the participation in this study * elective surgery planned during the participation in this study * patient is not willing or not capable to meet the study demands * patient does not agree to the forwarding of his/her pseudonymous data * patient without legal competence Exclusion criteria for randomisation: \- More than 4 consecutive weeks of freedom from seizure during baseline phase