Long-term Retention Rate of Zonisamide in Patients With Epilepsy: An Observational Study

Introduction: Zonisamide (ZNS) is an antiepileptic drug with a broad spectrum of action mechanisms. Although ZNS is usually indicated for the adjunctive treatment of partial seizures in Western countries, it has long been used for partial and generalized seizures as monotherapy or adjunctive treatment in South Korea and Japan. The present study was to evaluate the long-term retention rate of ZNS in clinical practice. Methods: This was a retrospective, single-center, long-term observational study. A total of 148 patients (82 men, 66 women; 14-85 years) who were treated with ZNS as monotherapy or adjunctive treatment were included. Zonisamide was administrated with a starting dose of 100 mg/d, and optimal-dose adjustments were made according to individual clinical responses. Efficacy and tolerability were analyzed during a 6-year follow-up. Results: The overall retention rate was 66.1% at 1-year and 55.1% at 6-year follow-up. Patients with monotherapy (70.8% vs 44.1%) and generalized seizures (71.6% vs 48.2%) were more likely to continue ZNS at 6-year follow-up compared with those with adjunctive therapy and partial seizures. The most common cause of discontinuation was adverse events such as somnolence, rash, and gastrointestinal problems. Conclusions: Our study shows the high retention rate of ZNS in the treatment of patients with epilepsy. The retention rate of ZNS was comparable with those of other antiepileptic drugs including lamotrigine, topiramate, and levetiracetam, and it can be suggested that ZNS can be considered for monotherapy and for the patients with generalized seizures.