Zonisamide

What is this medication for?

• Add-on for refractory epilepsy; may be used as monotherapy for initial treatment
• Refractory seizures — dose regimens not well defined

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Sedation, wobbliness/unsteadiness, inappetence (Reported, usually transient)
• Inappetence, diarrhea, vomiting, wobbliness/unsteadiness, somnolence (~50% of cats at 20 mg/kg/day in one study)

Worth a phone call to your veterinarian

• Liver injury (rare) (Possible — monitor)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Hypersensitivity to zonisamide or sulfonamides
• has or has had: Sulfonamide-related reactions (dry eye) theoretically possible though not yet reported

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Phenobarbital

Storage and handling

Store 25°C (excursions 15–30°C), dry place, protect from light.

Good to know

• Because it's a sulfonamide derivative, screen history for prior sulfa hypersensitivity before starting.
• Tolerance with reduced efficacy can develop after 2–3 months of chronic use — counsel owners this is possible.
• Generics now available, improving cost-accessibility relative to earlier years.