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.