Evaluation of antiseizure medications including zonisamide in feline idiopathic epilepsy at a referral hospital in Japan

Background: Idiopathic epilepsy in cats is a more common disease than previously thought, but little information is available about the medical treatment of feline idiopathic epilepsy. Aim: To assess the therapeutic efficacy and safety of antiseizure medication (ASM) for a minimum of six months, including zonisamide (ZNS), in feline idiopathic epilepsy at a referral hospital in Japan. Methods: Twenty cats diagnosed with idiopathic epilepsy treated with ASMs were retrospectively included. Results: Nine cats that were finally treated with phenobarbital (PB) monotherapy reached the primary goal (the seizure frequency after the treatment intervention was less than one seizure every 3 months). Three cats were treated with ZNS monotherapy and two reached the primary goal. Eight cats finally received combination therapy. Two of the three cats receiving PB and ZNS therapy achieved the primary goal, but one was considered no responder. Five cats (PB + diazepam (DZP), ZNS + DZP, and ZNS + levetiracetam + DZP) decreased the seizure frequency and reached the primary goal in all but one cat reached the secondary goal. Adverse events were observed in eight patients, but these were curable. Two patients had vomiting after ZNS monotherapy, one had diarrhea, and another was an increase in sleeping hours. Conclusion: PB was frequently used and seemed effective as both monotherapy and combination therapy. Some cats were treated with ASM protocols containing ZNS. ZNS may be available to treat idiopathic epilepsy in cats. However, ZNS administration may cause adverse events, such as gastrointestinal toxicity, in cats. [Open Vet J 2023; 13(7.000): 846-853]