Clinical efficacy and tolerability of zonisamide monotherapy in dogs with newly diagnosed idiopathic epilepsy: Prospective open-label uncontrolled multicenter trial

Abstract

Background: Zonisamide (ZNS) is a newer generation antiseizure medication (ASM) used to treat epilepsy in dogs and cats. However, scientific and clinical information, particularly regarding monotherapy, is limited. Objectives: To evaluate the antiseizure efficacy and tolerability of ZNS monotherapy in dogs with newly diagnosed idiopathic epilepsy (IE). Animals: Study included 56 client-owned dogs newly diagnosed with IE. Methods: This was a prospective multicenter, open-label, uncontrolled study. All dogs were ASM-naïve and had ≥2 seizures within 12 weeks. Dogs were administered 2.7-14.4 mg/kg ZNS PO q12h and followed up for ≥12 weeks. Data from the 12-week maintenance treatment period were compared with those from the 4- to 12-week pretreatment period for efficacy evaluation. Data from the entire ZNS administration period were used to assess tolerability. Results: Fifty-six dogs were included in our study. Of the dogs, 53 were assessed for efficacy; 40 (76%) had a ≥ 50% reduction in seizure frequency, and 29 (55%) achieved seizure freedom. For 90% of the dogs with ≥50% reduction in seizure frequency, the mean ZNS dose was 4.8 (range, 2.7-8.6) mg/kg q12h and the mean trough plasma ZNS concentration was 18.9 (range, 8.0-48.0) μg/mL. In 7 of the 56 dogs (13%), reduced activity, decreased appetite, vomiting, hindlimb weakness, soft stools, or constipation was observed, albeit mild and temporary. Laboratory tests revealed no relevant changes. Conclusions and Clinical Importance: Our study suggests that ZNS monotherapy is effective and well-tolerated in dogs with newly diagnosed IE.