Zonisamide for Dogs: An Option for Managing Seizures

While phenobarbital is widely regarded as the anti-seizure medication of choice for dogs, some dogs may require additional help or an entirely different approach. For those dogs, zonisamide (Zonegran) may be a good option. 

Keep reading to learn what this seizure medication is used for in dogs, its potential side effects, and other important things to know.

Zonisamide for dogs at a glance

What is zonisamide for dogs, and what is it used for?

Zonisamide is an anticonvulsant medication that is sometimes used to manage seizures in dogs. Zonisamide is FDA approved for use in humans, but not for use in dogs. However, veterinarians may use this medication off-label to control seizures in their canine or feline patients.

Zonisamide can be added to other anti-seizure medications for dogs who are having too many seizures. For example, zonisamide can be added to phenobarbital to improve seizure control.

Zonisamide can also be used as a dog’s main seizure medication. Some dogs can’t take popular anti-seizure medications. For example, dogs with liver disease may not be able to take phenobarbital. For these dogs, zonisamide can be used instead to manage seizures.

What is the typical dosage of zonisamide for dogs, and how is it given?

A dog’s dosage of zonisamide is based on their weight and whether they’re taking any other seizure medications.

For dogs who are not taking phenobarbital, the typical starting dosage is 5 mg per kilogram of body weight every 12 hours. 

Dogs who take phenobarbital usually need higher dosages of zonisamide. The dosage range for these dogs is 7 mg to 10 mg per kilogram of body weight every 12 hours.

Zonisamide comes in 25 mg, 50 mg, and 100 mg capsules. If these options don’t work for your dog, your veterinarian can order zonisamide as a compounded liquid. 

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• Seizures in dogs: Learn how to recognize a seizure, as well as the best options for managing seizures in dogs.

• Paying for seizure treatments: Find out how one dog owner was able to afford her dog’s seizure medications and what tips she has for other pet parents.

• Phenobarbital for dogs: Phenobarbital is one of the most common anti-seizure medications for dogs. Here’s what to expect if your dog is prescribed phenobarbital.

Dogs may develop a tolerance to zonisamide over time. So your dog’s dosage may need to eventually increase if they are taking the medication long term.

Zonisamide can cause birth defects in human babies. So dog owners who are pregnant or trying to get pregnant should use caution when giving zonisamide to their pet. Wear gloves when you give the medication to your dog and wash your hands afterward.

What should you do if your dog misses a dose of zonisamide?

If you forget to give your dog a dose of zonisamide, give them the missed dose as soon as you remember. Then, continue giving them the medication as prescribed. 

If it’s almost time for the next dose when you remember, skip the missed dose. Do not double up on zonisamide doses to make up for a missed one.

If you are unsure how to get back on track after a missed dose, it is best to contact your veterinarian.

What are the common side effects of zonisamide in dogs?

The most common side effects of zonisamide in dogs include:

• Sedation

• Ataxia (clumsy gait and incoordination)

• Lack of appetite

• Vomiting

If your dog vomits after taking zonisamide, you can try giving them the medication with food to reduce the likelihood of this side effect.

What are the most serious risks of zonisamide for dogs?

A rare but potentially life-threatening risk of zonisamide for dogs is hepatopathy (development of liver disease). This is estimated to occur in less than 1% of dogs treated with zonisamide. 

While rare, severe kidney disease has also been reported in dogs taking zonisamide. In some cases, this can lead to kidney and/or bladder stones.

Dogs who are allergic to sulfonamide-containing medications may have an increased risk of developing an allergic reaction to zonisamide. 

Zonisamide should not be given to pregnant dogs. Giving this medication to a pregnant dog may result in heart defects in their puppies. 

Does zonisamide interact with any other dog medications?

Zonisamide can interact with other dog medications, including phenobarbital.

Dogs taking phenobarbital may require higher dosages of zonisamide. Zonisamide may also increase concentrations of phenobarbital in the body, which can harm the liver. If your dog takes both of these medications, your veterinarian will want to closely monitor them for signs of an interaction. 

Zonisamide can also interact with carbonic anhydrase inhibitors. These medications are used to treat glaucoma in dogs. Examples include acetazolamide and dorzolamide.

Before your dog starts treatment with zonisamide, tell your veterinarian about any other medications your dog takes.

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Written by:

Rhiannon Koehler, DVM, MPH

Rhiannon Koehler, DVM, MPH has been involved in veterinary medicine for over a decade. Her clinical practice has mostly revolved around providing care to shelter animals, low-cost services to underprivileged families, and wellness care for pet parents.

Edited by:

Renée Fabian, MA

Renée Fabian is the senior pet health editor at GoodRx. She’s worked for nearly 10 years as a journalist and editor across a wide range of health and well-being topics.

Reviewed by:

Ghanasyam Bey, DVM

Ghanasyam Bey, DVM, is from Cleveland, Ohio, and attended Princeton University for undergraduate studies. After a year of biology research at Duke University, he attended Ohio State College of Veterinary Medicine.

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