By Lauren Forsythe, PharmD, DICVP; Rania Gollakner, BS, DVM, MPH

What is zonisamide?

Zonisamide (brand name: Zonegran®) is an anticonvulsant (antiseizure) medication that is used either as an initial therapy for epilepsy or as an add-on drug for seizures that are difficult to control.

Its use in cats and dogs to treat seizures is “off label” or “extra label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully, as their directions may be significantly different from those on the label.

How is zonisamide given?

  • Give zonisamide by mouth, as an oral capsule or compounded into an oral liquid.
  • Give with or without food.
  • If your pet vomits or acts sick after receiving it, give this medication with food or a small treat.

The medication should begin working within 1-2 days. Do not stop this medication suddenly or else seizures may occur.

Zonisamide is considered a hazardous drug. Wear gloves when handling the medication, and do not handle if you are pregnant or nursing.

What if I miss giving my pet the medication or my shipment is late?

If you miss a dose, give it when you remember. However, if it is close to the time for the next dose, skip the dose you missed, give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Zonisamide may be associated with the following side effects in dogs:

  • sedation
  • incoordination while walking
  • vomiting
  • lack of appetite

Contact your veterinarian if these signs are severe.

Rare side effects in dogs include:

  • liver disease
  • urinary stones 
  • aggression

Contact your veterinarian immediately if your pet stops eating, becomes dramatically lethargic, or develops a yellow color of the skin, gums, or whites of the eyes.

In cats, side effects may include:

  • inappetence (lack of appetite)
  • diarrhea
  • vomiting
  • incoordination while walking 
  • sleepiness

The effects of this short-acting medication typically last only 24 hours in dogs. In cats, it can last for approximately 48 hours, and therefore side effects may last for 1-2 days even after this medication is discontinued. This time may increase if your pet has decreased liver or kidney function.

Are there any risk factors for this medication?

Zonisamide SHOULD NOT be used in pets that:

  • are hypersensitive or allergic to it
  • have liver disease
  • are breeding or pregnant

Zonisamide should be used with caution in pets that:

  • have a hypersensitivity or an allergy to sulfonamide drugs
  • are nursing, as it is unknown at this time if zonisamide is excreted in maternal milk

Are there any drug interactions I should be aware of?

When given with phenobarbital, zonisamide is cleared from the body more quickly, and therefore higher doses of zonisamide may be required or phenobarbital doses may need to be decreased. This effect from phenobarbital can last up to 10 weeks after phenobarbital use has been discontinued.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

  • Your veterinarian may monitor your pet’s blood zonisamide levels. 
  • Monitor your pet for any adverse effects. 
  • Track the occurrence of seizures while your pet is taking this medication to help monitor how well this medication is working.
  • If your pet stops eating, becomes dramatically lethargic, or develops a yellow color of the skin, gums, or whites of the eyes, contact your veterinarian immediately.

How do I store zonisamide?

Zonisamide should be stored at 25°C (76°F). Brief exposure to temperatures between 15°C (59°F) and 30°C (86°F) is permitted. Capsules should be protected from light and be stored in a dry place.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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