Efficacy of monotherapy with zonisamide and proposed reference interval in dogs with epilepsy: a cohort of 207 dogs (2011-2021).

Abstract

BACKGROUND: Zonisamide (ZNS) has become a popular antiseizure medication (ASM) to treat epilepsy in dogs. Dose adjustments based on plasma ZNS concentrations facilitate management, but efficacy evidence is limited. No reference interval (RI) is established in dogs. HYPOTHESIS/OBJECTIVES: To assess ZNS efficacy and establish an RI for dogs with epilepsy. ANIMALS: Two hundred seven dogs with non-structural epilepsy received ZNS monotherapy, with samples submitted for therapeutic drug monitoring (TDM). METHODS: In this retrospective observational study, ZNS information was collected from the TDM data record library between November 2011 and May 2021. Exclusion criteria were structural epilepsy, receiving other ASMs, dogs' age&#xa0;>6&#xa0;years, or a duration of ZNS <3&#xa0;months. Zonisamide response was assessed as described in the International Veterinary Epilepsy Task Force (IVETF) consensus. Plasma ZNS concentrations from responders (categories 1 [seizure freedom] and 2 [partial response]) were evaluated at the established RI. RESULTS: Two hundred seven dogs could be assigned to IVETF response categories 1-3. The proportion of responders (59%, n&#xa0;=&#xa0;123), including categories 1 (29%) and 2 (30%), was higher than non-responders (category 3, 41%, n&#xa0;=&#xa0;84; P&#xa0;<&#xa0;.01). Based on the responders, an RI of 10-55&#xa0;&#x3bc;g/mL is proposed. CONCLUSIONS AND CLINICAL IMPORTANCE: This study demonstrated that ZNS monotherapy is effective for treatment of non-structural epilepsy. The proposed RI, 10-55&#xa0;&#x3bc;g/mL, is a broader range than that in human medicine, 10-40&#xa0;&#x3bc;g/mL.