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 6 years, or a duration of ZNS 3 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 = 123), including categories 1 (29%) and 2 (30%), was higher than non-responders (category 3, 41%, n = 84; P .01). Based on the responders, an RI of 10-55 μg/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 μg/mL, is a broader range than that in human medicine, 10-40 μg/mL.
Thungrat et al. (Thu,) studied this question.