Zonisamide (ZNS) efficacy and safety in epilepsy have been demonstrated in four double-blind, placebo-controlled studies. In the present article, we examined all long-term studies performed with this drug. Nine open-label studies, in which ZNS had been administered as an add-on or as monotherapy to epileptic patients for at least 6 months, were selected for our analysis. Four outcome measures were searched. Retention of this drug after 1 year varied between 45% and 65%. The percentages of patients achieving a >/=50% seizure reduction, with respect to baseline, ranged between 37% and 65%. In patients with drug-resistant forms of epilepsy, the percentage of patients reaching a 6-month seizure freedom period was 9%. The percentages of patients who discontinued the experimental drug due to adverse effects ranged between 4% and 24%. Somnolence and dizziness were the most frequently reported adverse effects. Long-term studies demonstrate that ZNS has a good efficacy and tolerability profile, and support its use as adjunctive therapy for epileptic patients.
Keywords: antiepileptic drugs; epilepsy; long-term treatment; review; zonisamide.