Zonisamide
Zonisamide is an anticonvulsant.
Group
Anticonvulsant
Mechanism of Action
Modulates voltage-dependent sodium and T-type calcium channels, reducing excessive neuronal firing.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Epilepsy | 5 mg/kg | PO | Every 12 h | Start here and titrate using response and concentrations. |
| Epilepsy with phenobarbital | 10 mg/kg | PO | Every 12 h | |
| Epilepsy | 5–10 mg/kg | PO | Every 12 h | Higher end often needed with phenobarbital. |
| Initial monotherapy | 3–5 mg/kg | PO | Every 12 h |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Epilepsy | 5 mg/kg | PO | Every 12 h | |
| Epilepsy | 10 mg/kg | PO | Every 24 h | |
| Epilepsy | 5 mg/kg | PO | Every 12–24 h | |
| Epilepsy | 5–10 mg/kg | PO | Every 24 h | |
| Epilepsy higher-dose alternative | 10–20 mg/kg | PO | Every 24 h | Separate older reported range; monitor sedation, appetite and serum levels closely. |
Indications
- Refractory epilepsy and adjunct seizure control
- Epilepsy
- Initial monotherapy
- Epilepsy higher-dose alternative
Contraindications
- Sulfonamide sensitivity requires caution.
Interactions
- Phenobarbital increases clearance; other CNS depressants compound sedation.
Adverse effects
- Sedation, ataxia, vomiting, hepatic injury and altered thyroid hormone results.
Toxicity
Prolonged CNS and cardiovascular depression can follow overdose because elimination is slow; supportive monitoring may be needed for several days.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Zonisamide capsule 25 mg | Capsule | 25 mg / capsule | PO |
| Zonisamide capsule 50 mg | Capsule | 50 mg / capsule | PO |
| Zonisamide capsule 100 mg | Capsule | 100 mg / capsule | PO |
Monitoring and Administration
Follow seizure control, liver function and thyroid values. Reported suggests serum 10-40 mcg/mL, but feline adverse effects have occurred above 20 mcg/mL; interpret individually. Compounded stability is unestablished.
Rectal administration is not recommended: experimental 20 or 30 mg/kg doses in a 100 mg/mL capsule-derived suspension did not achieve therapeutic concentrations.