Zonisamide for Dogs and Cats: Uses, Dosage, and Side Effects

Zonisamide is a prescription anticonvulsant medication veterinarians use to help prevent seizures in dogs and cats. It may be prescribed alone or in combination with other anti-seizure medications, such as phenobarbital.

Here’s how zonisamide works, when it’s prescribed, possible side effects, dosing guidance, and important safety information.

What Is Zonisamide?

Zonisamide is a prescription anticonvulsant (anti-seizure) medication used to help prevent seizures in dogs and cats.

Common uses: Veterinarians may prescribe zonisamide to:

• Help prevent seizures in dogs
• Help prevent seizures in cats
• Use alone or in combination with other anti-seizure medications, such as phenobarbital

FDA approval: Zonisamide is FDA-approved for human use under the brand names Zonegran®, Zonisade®, and generic zonisamide.

Although zonisamide is not FDA-approved as a veterinary medication, veterinarians may legally prescribe it extra-label (off-label) when they determine it is appropriate for a pet.

Compounded zonisamide: In some cases, your veterinarian may recommend a compounded formulation when:

• Your pet has difficulty taking the commercially available formulation.
• The required dosage strength is not commercially available.
• Your pet is allergic to an ingredient in the FDA-approved medication.

Compounded medications are not FDA-approved. They are prepared by a veterinarian or licensed pharmacist to meet an individual patient's specific needs.

How Zonisamide Works

Zonisamide helps stabilize electrical activity in the brain to reduce the likelihood of seizures.

Although its exact mechanism of action is not fully understood, zonisamide is believed to regulate the movement of key ions, including sodium and chloride, which helps stabilize electrical activity in the nervous system.

Zonisamide may also influence the neurotransmitters serotonin and dopamine.

How To Give Zonisamide

Give zonisamide exactly as directed by your veterinarian.

Administration tips:

• Follow the directions on the prescription label or those provided by your veterinarian.
• Zonisamide is typically given once or twice daily, depending on your pet's species and whether other anti-seizure medications are being used.
• Zonisamide may be given with or without food.
• If your pet develops digestive upset, try giving the medication with food or a small meal.
• Do not stop giving zonisamide unless your veterinarian instructs you to do so.

Missed a Dose?

If you miss a dose of zonisamide, contact your veterinarian for guidance. 

In many cases, they may recommend giving the missed dose as soon as you remember and then waiting the normal interval before the next dose. In other cases, they may advise skipping the missed dose and resuming the normal dosing schedule.

Do not give extra or double doses.

Zonisamide Side Effects

Zonisamide is generally well tolerated, but side effects can occur. As with many anti-seizure medications, drowsiness is the most common side effect.

Additional side effects may include:

• Lethargy
• Vomiting
• Diarrhea
• Loss of appetite
• Yellowing of the eyes or skin
• Incoordination

Human Side Effects

Although zonisamide is also prescribed for people, human and veterinary doses differ.

If you accidentally ingest a pet medication, contact your physician immediately or call the National Poison Control Center at 800-222-1222.

Monitoring Your Pet

Your veterinarian may recommend monitoring or routine testing while your pet is taking zonisamide based on their individual health needs, other medications, and the condition being treated.

When To Call Your Veterinarian

Contact your veterinarian if:

• Your pet develops severe side effects.
• Your pet's condition worsens or does not improve with treatment.
• You suspect your pet has received an overdose.
• You have additional questions or concerns about using zonisamide.

Zonisamide Overdose

A zonisamide overdose can cause serious side effects and requires immediate veterinary attention.

Signs of an overdose may include:

• Lethargy
• Incoordination
• Vomiting
• Diarrhea
• Loss of appetite
• Yellowing of the eyes or skin
• Dry eye

The severity of symptoms depends on how much medication was ingested.

If you suspect your pet has received an overdose, contact your veterinarian immediately, seek emergency veterinary care, or contact an animal poison control center. Consultation fees may apply.

• Pet Poison Helpline: (855) 764-7661
• ASPCA Animal Poison Control: (888) 426-4435

How To Store Zonisamide

Store zonisamide according to the product label to help maintain its safety and effectiveness.

Storage instructions:

• Store zonisamide at controlled temperatures around 77 F (25 C).
• Brief exposure to temperatures between 59 F and 86 F (15 C–30 C) is acceptable.
• Always confirm storage instructions by reading the product label.
• Keep the container tightly closed to protect the medication from moisture and light.
• Store compounded formulations according to the instructions provided by the compounding pharmacy.
• Keep out of reach of children and pets.