zonisamide
Zonisamide is an antiepileptic medication that’s used to treat seizures in dogs and cats. It’s a human medication that’s used for pets since there’s no animal-only formulation. The vet might prescribe zonisamide alone to treat seizures, or they might add it to other seizure medications that aren’t working well enough. Zonisamide comes as capsules but can also be made into a liquid form by a compounding pharmacy. The dose is based on your pet’s weight, and it's usually given once or twice per day. Some side effects are sleepiness and low appetite.
What is Zonisamide for pets?
What is Zonisamide for pets used for?
How Zonisamide for pets works
Zonisamide is a type of antiepileptic medication. Experts don't know exactly how it works. But they believe it calms the electrical signals in the brain. This helps prevent seizures from happening.
Drug Facts
More on Zonisamide essentials
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What are the side effects of Zonisamide for pets?
Common Side Effects
- Sleepiness
- Low energy
- Low appetite
- Trouble walking
- Low appetite
- Diarrhea
- Vomiting
Other Side Effects
Serious Side Effects
- Liver damage: loss of appetite; vomiting; yellowing of the skin, gums, or eyes
- Allergic reaction: rash, hives, fever, swelling, trouble breathing, shock, collapse
- High acid levels in the body: panting, sleepiness, tiredness, muscle problems, irregular heartbeat, low blood pressure
The following side effects have also been reported
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
More common
Discouragement
double vision
feeling sad or empty
irritability
lack of appetite
loss of interest or pleasure
mood or mental changes
shakiness or unsteady walking
tiredness
trouble with concentrating
trouble with sleeping
Less common
Agitation
bruising
delusions
hallucinations
large, flat blue or purplish patches on the skin
rash
Incidence not known
Blurred vision
change in near or distance vision
difficulty in focusing eyes
increase in frequency of seizures
swelling of the face
yellow eyes or skin
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
More common
Abdominal or stomach pain
difficulty with memory
dizziness
double vision
headache
loss of appetite
restlessness
sleepiness
unusual drowsiness
unusual tiredness or weakness
Less common
Aching muscles or joints
acid or sour stomach
bad, unusual, or unpleasant taste in the mouth
belching
change in taste
chills
difficulty with speaking
difficulty with thinking
general ill feeling
headache
indigestion
mental slowness
nervousness
runny or stuffy nose
tingling, burning, or prickly feelings on the skin
uncontrolled, back and forth, or rolling eye movements
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
Pros and cons of Zonisamide for pets
Pros
Can use alone or with other seizure medications to manage seizures in pets
Liquid form can be made by some special pharmacies depending on your pet’s needs
Usually well tolerated
Cons
Will need to get your pet’s blood drawn a week after starting and also after each dose change
Might have to give to your pet for the rest of their life
Might cause allergic reaction if you or your pet has a “sulfa” allergy
Pharmacist tips for Zonisamide for pets
If you’re pregnant, trying to get pregnant, or breastfeeding, be careful when you’re handling zonisamide. Wear gloves if you need to touch the medication and be sure to wash your hands afterwards. Zonisamide can cause harm to your baby.
If you have a “sulfa” allergy, be careful while handling zonisamide. Or, you can ask someone else without the allergy to give your pet the medication. Zonisamide is a “sulfa” drug. So if you have this allergy, touching the medication could cause an allergic reaction.
You can give zonisamide with or without food. If your pet has an upset stomach after taking the medication, try giving it with a small amount of food or a treat next time. Ask your vet about tips on how to get your pet to take pills.
If your pet needs a zonisamide dose that isn’t easy to find or has trouble swallowing capsules, ask your vet about a liquid version of the medication that’s specially made by the pharmacy. Follow their instructions to measure and give the medication. Always use a dosing syringe or cup (not a household spoon) so your pet takes the right amount. Ask how to store the liquid properly.
Keep a log of your pet’s seizures to track how well zonisamide is controlling their seizures. It also might be helpful to take a video of the seizure. Share any notes or videos with the vet. They can decide if zonisamide is right for your pet, if the dose should be changed, or if your pet needs a different medication to control seizures.
Don’t stop giving your pet zonisamide suddenly. This can make seizures come back. If you want your pet to stop taking zonisamide, talk to your vet first. They’ll give you instructions on how to slowly lower the dose over time to stop the medication safely. Be sure to time refills well so your pet doesn’t suddenly run out of zonisamide.
If you forget to give your pet zonisamide, don’t double their dose or give extra medication. Wait until the next time they usually take the medication to give the regular dose to your pet. Giving too much zonisamide raises the risk of side effects.
If your pet gets pregnant while taking zonisamide, talk to your vet about whether to keep giving the medication to them. Zonisamide isn’t usually recommended for pregnant animals because it can harm the unborn babies. Your vet can discuss the risks and benefits for your pet.
Frequently asked questions about Zonisamide for pets
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What are the risks and warnings for Zonisamide for pets?
Zonisamide can cause some serious health issues. This risk might be even higher for certain pets. If this worries you, talk to your veterinarian about other options.
Risk of harm to the liver
Risk factors: Dogs | High zonisamide dose | Taking zonisamide for a long time
The risk for liver toxicity from zonisamide is low. But talk to your vet if you know your pet already has liver problems to make sure this medication is safe for them. If your pet has signs of liver damage while taking zonisamide, talk to a veterinarian immediately. Look out for signs like not eating, vomiting, overly tired, and yellowing of the skin, eyes, or gums.
Allergic reaction
Risk factors: Pets with a sulfonamide (“sulfa”) allergy | Doberman pinscher breed of dogs
Tell the vet if your pet has a sulfonamide or “sulfa” allergy before giving zonisamide. Pets with this allergy shouldn’t take this medication unless the benefits are greater than the risks. Some dog breeds, like Doberman pinschers, are more likely to be sensitive to sulfonamides like zonisamide. These dogs should avoid taking zonisamide if possible to be safe.
A mild allergic reaction to zonisamide can look like hives or a fever. More serious reactions include swelling, blood problems, or anaphylaxis (e.g., trouble breathing, shock, collapse). Get help from a veterinarian right away if your pet has an allergic reaction to zonisamide.
Higher acid levels in the body
Although rare, zonisamide can lower how well your pet’s kidneys can remove acid from the body. Too much acid can build up, which can lead to a medical emergency called metabolic acidosis. Signs of metabolic acidosis in pets include heavy panting, being very sleepy or tired, sleepiness, an irregular heartbeat, and low blood pressure. Call your vet right away if you see any signs of metabolic acidosis while your pet is taking zonisamide.
Withdrawal seizures
Risk factors: Lowering the dose or stopping zonisamide too suddenly | Missing zonisamide doses
If you lower the dose or stop giving zonisamide suddenly, your pet might have seizures again. Talk to your vet before changing or stopping your pet’s medication to make sure it’s safe. The vet might slowly lower the dose over time to do this safely.
Harm to unborn puppies or kittens
Risk factors: Pregnant pets
Zonisamide isn’t recommended for pregnant dogs and cats. This is because it can harm the unborn babies and cause heart problems. But sometimes, the vet might decide that controlling your pet’s seizures outweighs the risk of harming the puppies or kittens. Talk to your vet if your pet is pregnant or could become pregnant before starting zonisamide.
Zonisamide dosage forms
Typical dosing for Zonisamide for pets
The dose is based on your pet’s weight.
Dogs
Taking zonisamide alone: The typical starting dose is 5 mg/kg by mouth every 12 hours.
Taking zonisamide with phenobarbital: The recommended starting dose is 10 mg/kg by mouth every 12 hours.
Cats: The typical starting dose is 5 mg/kg to 10 mg/kg by mouth every 24 hours. Some vets might prefer to give this medication every 12 hours.
The vet might change the dose based on the zonisamide levels in your pet’s blood. This helps make sure the medication is safe and works well to control your pet’s seizures.
Interactions between Zonisamide and other drugs for pets
Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
- Methenamine
Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Calcifediol
- Methotrexate
- Orlistat
Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Aminolevulinic Acid
- Ginkgo
How much does Zonisamide cost?
Zonisamide contraindications for pets
Allergy to sulfonamides (“sulfa” drugs)
What are alternatives to Zonisamide for pets?
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References
Best studies we foundAkin, E. Y. (2020). Treatment plans for routine and refractory canine epilepsy. Today’s Veterinary Practice.
Aurobindo Pharma Limited. (2023). Zonisamide capsule [package insert]. DailyMed.
Castel, A. (2025). Anticonvulsants for treatment of animals. Merck Manual Veterinary Manual.
Center, S. A. (2024). Hepatotoxins in small animals. Merck Manual Veterinary Manual.
Gelatt, K. N. (2024). Glaucoma in dogs. Merck Manual Veterinary Manual.
Hodshon, A., et al. (2017). Antiseizure medications for cats. Clinician’s Brief.
Hopper, K., et al. (2012). Incidence, nature, and etiology of metabolic acidosis in dogs and cats. Journal of Veterinary Internal Medicine.
Itoi, T., et al. (2022). Distal renal tubular acidosis and lethargy associated with zonisamide treatment in a dog with idiopathic epilepsy. Veterinary Medicine and Science.
Jukier, T. (2024). Antiseizure medications for dogs and cats. Today’s Veterinary Practice.
Kanazono, S., et al. (2021). Abnormal behavior episodes associated with zonisamide in three dogs: A case report. Frontiers in Veterinary Science.
Lavely, J. A. (2014). Pediatric seizure disorders in dogs and cats. The Veterinary Clinics of North America: Small Animal Practice.
McAtee, B. B., et al. (2017). Liver enzyme interpretation and liver function tests. Today’s Veterinary Practice.
Mealey, K. L. et al. (2021). Top 5 breed-specific considerations to avoid adverse drug effects. Clinician's Brief.
Mercer, M. A. (2025). Sulfonamides and sulfonamide combinations use in animals. Merck Manual Veterinary Manual.
Plumb’s Drug Handouts. (2024). Zonisamide.
Podell, M., et al. (2016). 2015 ACVIM small animal consensus statement on seizure management in dogs. Journal of Veterinary Internal Medicine.
Saito, M., et al. (2024). Clinical efficacy and tolerability of zonisamide monotherapy in dogs with newly diagnosed idiopathic epilepsy: Prospective open-label uncontrolled multicenter trial. Journal of Veterinary Internal Medicine.
Smith, T. K., et al. (2022). Incidence of hepatopathies in dogs administered zonisamide orally: A retrospective study of 384 cases. Journal of Veterinary Internal Medicine.
Tizard, I. R. (2024). Hypersensitivity diseases in animals. Merck Manual Veterinary Manual.
Waddell, L. S. (2013). The practitioner’s acid-base primer: Differential diagnoses and treatment. Today’s Veterinary Practice.
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