Update (June 19, 2026): Zonisamide Reduced Seizures and Was Well Tolerated in 57 Cats - Multicenter Retrospective Study

TL;DR

A 57-cat multicenter retrospective study found zonisamide reduced seizure frequency and was well tolerated in most cats, extending the small body of feline-specific antiseizure evidence beyond phenobarbital.

What just dropped

• A multicenter retrospective study of 57 cats with a history of seizures reported a median decrease of one seizure per month after oral zonisamide (P = .001), with a similar reduction in seizure days per month (Djani 2024, https://europepmc.org/articles/PMC10937493).
• In the subgroup with idiopathic epilepsy, the median reductions were larger (one and two, respectively).
• The most common clinical adverse effects were hyporexia (17%), sedation (17%), ataxia (11%), and emesis (5%); a few cats developed mild nonregenerative anemia, mild metabolic acidosis, or mild increases in ALT and ALP.
• The authors concluded that zonisamide was well tolerated and efficacious in controlling seizure activity in most cats.

Context

Evidence-based options for antiseizure therapy in cats beyond phenobarbital remain limited, and this cohort is one of the larger feline-specific datasets to date. It complements the canine literature: a prospective multicenter trial in 56 dogs with newly diagnosed idiopathic epilepsy found zonisamide monotherapy produced a 50% or greater seizure reduction in 76% of dogs and seizure freedom in 55%, also with a mild and transient adverse-effect profile (Saito 2024, https://europepmc.org/articles/PMC11256125). The feline data are retrospective and uncontrolled, so they describe association rather than proving efficacy, but they support zonisamide as a reasonable consideration when phenobarbital is unsuitable or insufficient.

What this changes in the zonisamide evergreen

Our zonisamide review (https://www.thevoyage.ai/forvets/knowledge/zonisamide-canine-epilepsy) is anchored on canine data. This feline cohort adds species-specific tolerability and effectiveness signals — and a distinct adverse-effect pattern — that are worth flagging for clinicians extrapolating zonisamide use to cats. As always, dosing should be set from a current formulary, not extrapolated from any figure here.

References

1. Djani DM, Liou M, Aravamuthan S, Lau V, Cameron S. 2024. A retrospective study of the efficacy of zonisamide in controlling seizures in 57 cats. J Vet Intern Med 38(2):1092-1100. https://europepmc.org/articles/PMC10937493
2. Saito M, Nomura A, Hasegawa D, et al. 2024. Clinical efficacy and tolerability of zonisamide monotherapy in dogs with newly diagnosed idiopathic epilepsy: Prospective open-label uncontrolled multicenter trial. J Vet Intern Med 38(4):2228-2236. https://europepmc.org/articles/PMC11256125

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