Zonisamide (ZNS) is effective as monotherapy for canine idiopathic epilepsy (IE), with 55–76% of dogs achieving ≥50% seizure frequency reduction and 55% achieving complete seizure freedom. The standard oral dose is 5–10 mg/kg PO q12h, targeting a trough serum concentration of 10–40 μg/mL.New Zealand Vet…+2
Efficacy data support ZNS as a first-line option. In dogs with newly diagnosed IE, 76% achieved ≥50% reduction in seizure frequency and 55% achieved seizure freedom on ZNS monotherapy; the mean effective dose in responders was 4.8 mg/kg q12h (range 2.7–8.6 mg/kg q12h), with mean trough plasma concentrations of 18.9 μg/mL (range 8.0–48.0 μg/mL).Journal of Vete… An earlier study reported 60% of dogs as favorable responders (≥50% reduction in monthly seizure frequency) at a mean dose of 7.92 mg/kg q12h.New Zealand Vet…
The published dose range is 2.7–15 mg/kg PO q12h across studies, with the MSD Veterinary Manual citing 5–10 mg/kg PO q12h as the standard clinical range.New Zealand Vet…+2 Steady state is achieved within approximately 1 week.MSD Vet Manuals The half-life in dogs is 18–28 hours, supporting twice-daily dosing.MSD Vet Manuals
A critical pharmacokinetic interaction exists with phenobarbital (PB): dogs receiving concurrent PB require nearly twice the ZNS dose to achieve and maintain therapeutic serum concentrations, due to cytochrome P450 induction by PB.MSD Vet Manuals ZNS co-administration does not meaningfully alter levetiracetam extended-release pharmacokinetics.Journal of Vete…
Adverse effects are generally mild and transient. In the largest monotherapy trial, 13% of dogs experienced reduced activity, decreased appetite, vomiting, hindlimb weakness, soft stools, or constipation, all of which were mild and temporary, with no relevant changes on laboratory testing.Journal of Vete… Idiosyncratic reactions — including neutropenia, erythema multiforme, and acute hepatopathy — are reported but uncommon; severe acute hepatopathy has been described in individual cases.Journal of Vete… Experimental dosing at 75 mg/kg/day (approximately 5× the recommended clinical dose) produced persistent increases in serum alkaline phosphatase and decreases in serum albumin, but this has not been characterized at clinical doses.Journal of Vete…
ZNS compares favorably to PB on tolerability. Seizure freedom rates with PB monotherapy range from 40–85% in dogs with IE, but PB carries a relatively narrow therapeutic index with more frequent adverse effects.Journal of the… ZNS does not induce hepatic microsomal enzymes, which is a pharmacokinetic advantage when polytherapy is anticipated.MSD Vet Manuals
| Drug | Dose | ≥50% Responder Rate | Seizure Freedom Rate | Key Caveat |
|---|---|---|---|---|
| Zonisamide (monotherapy) | 2.7–14.4 mg/kg PO q12h | 76%Journal of Vete… / 60%New Zealand Vet… | 55%Journal of Vete… | Doubles dose needed if combined with PBMSD Vet Manuals |
| Phenobarbital (monotherapy) | 2 mg/kg PO q12h (initial) | Not reported as % in sources | 40–85%Journal of the… | Narrow therapeutic index; more frequent AEsJournal of the… |
Would you like guidance on therapeutic drug monitoring — specifically when to check ZNS trough levels and how to interpret them in the context of clinical response?