Side Effects of Anti-Epileptic Drugs in Dogs with Epilepsy
- Christina Roed
- May 30, 2023
- 5 min read
Updated: Oct 29
Why anti-epileptic drugs are important
If your dog has been diagnosed with epilepsy, you’ve probably been prescribed one or more anti-epileptic drugs (AEDs). These medicines can feel intimidating at first, but they’re often life-changing for dogs with seizures.
AEDs help reduce how often seizures happen and how severe they are, allowing your dog to live a happier, more stable life. The goal of treatment is always to find the lowest possible dose that keeps seizures under control while keeping side effects minimal.
Understanding how each medication works can help you feel confident in your dog’s treatment plan and recognise what’s normal during the adjustment period.
How anti-epileptic drugs work
Seizures happen when groups of brain cells start firing too quickly and all at once. Anti-epileptic drugs calm this overactivity in different ways:
Boosting inhibition: Some drugs make the brain’s calming messenger, called GABA (gamma-aminobutyric acid), work more effectively.
Reducing excitation: Others stabilise the channels that let sodium or calcium flow into nerve cells, making them less excitable.
Regulating communication: A few medicines control how neurotransmitters are released between nerve cells.
Each medication takes a slightly different approach, but all share the same goal, to help your dog’s brain stay balanced and reduce seizure activity.
Common anti-epileptic medications and their effects
Phenobarbital
How it works
Phenobarbital enhances GABA activity, helping to calm nerve signals in the brain. It’s one of the oldest and most effective anti-seizure medicines for dogs.
Why it helps
It’s usually the first drug your vet will try because it controls seizures in a large number of dogs. The dose can be adjusted based on blood levels to make sure your dog is getting just the right amount.
Possible side effects
Sleepiness or wobbliness, especially when first starting
Increased thirst and appetite
Weight gain
Increased urination
Higher liver enzyme readings on blood tests
Regular blood tests are important to make sure your dog’s liver stays healthy and that the medication level is in the correct range.
Potassium Bromide (KBr)
How it works
Potassium bromide helps the brain’s calming system (GABA) work more effectively, which reduces how easily neurons fire.
Why it helps
It’s often used if phenobarbital alone isn’t enough or can’t be used. Because it builds up slowly in the body, your vet may take several weeks to reach the right dose.
Possible side effects
Sleepiness or loss of coordination
Increased thirst and urination
Increased appetite and weight gain
Mild stomach upset
Keeping your dog’s diet consistent helps, since dietary salt affects how bromide is processed by the body.
Levetiracetam
How it works
Levetiracetam acts on a protein in brain cells called SV2A, which helps control the release of neurotransmitters. This helps stabilise electrical activity in the brain.
Why it helps
It’s well tolerated, doesn’t affect the liver, and has very few interactions with other medications. It’s often used as an additional treatment for dogs who need extra control.
Possible side effects
Mild sleepiness or fatigue
Reduced appetite
Occasional stomach upset
Rarely, mild behavioural changes such as restlessness
Side effects are usually temporary and often improve as your dog adjusts.
Zonisamide
How it works
Zonisamide reduces brain excitability by blocking sodium and calcium channels in nerve cells.
Why it helps
It can be used on its own or with other anti-seizure drugs. It’s generally well tolerated and suitable for long-term use in many dogs.
Possible side effects
Sleepiness or mild wobbliness
Loss of appetite or vomiting
Rare allergic skin reactions
Very rarely, liver or kidney changes (your vet will monitor this)
If your dog ever shows signs of a rash, yellow gums, or unusual tiredness, call your vet straight away.
Imepitoin
How it works
Imepitoin gently boosts GABA activity in the brain, helping to calm electrical signals without causing deep sedation.
Why it helps
It’s licensed specifically for idiopathic epilepsy in dogs and can be used as a first-line treatment. It starts working quickly and is often well tolerated.
Possible side effects
Mild sleepiness or unsteady walking, especially in the first few days
These effects usually fade as your dog’s body adapts
Finding the right balance
Every dog responds differently to medication. What matters most is finding the combination and dose that keeps seizures under control while maintaining your dog’s quality of life.
Important things to remember
Never stop or reduce an anti-seizure medication suddenly. This can trigger more severe seizures. Always taper under veterinary supervision.
Keep a seizure diary noting the date, time, length, and type of each seizure, along with any possible triggers or side effects.
Blood tests are a normal part of epilepsy management and help ensure that your dog’s organs are coping well with the medication.
Discuss any concerns with your vet before making changes, even small adjustments can make a big difference.
When to call your vet
Contact your vet if you notice any of the following:
Persistent vomiting, diarrhoea, or loss of appetite
Severe or ongoing drowsiness that doesn’t improve
Yellowing of the gums or eyes (possible liver issue)
Sudden worsening of seizures or change in seizure pattern
Signs of allergic reaction such as facial swelling, rash, or breathing changes
Your vet may recommend adjusting the dose, changing the medication, or adding another drug for better control.
The bigger picture: Side Effects of Anti-Epileptic Drugs in Dogs
Epilepsy can feel overwhelming, but these medicines save and transform lives. The science behind them is strong, and decades of veterinary experience show that most dogs live long, active, and happy lives once their treatment plan is stabilised.
Side effects of Anti-Epileptic Drugs in dogs often settle as your dog adapts, and your vet will help manage any that persist. Remember that seizure control is a process, it can take time to find what works best for your individual dog.
With regular monitoring, good communication, and a calm approach, anti-epileptic drugs can give dogs with epilepsy the stability and quality of life they deserve.
References
Bhatti S. F. M., De Risio L., Muñana K., et al. (2015). International Veterinary Epilepsy Task Force consensus proposal: Medical treatment of canine epilepsy in Europe. BMC Veterinary Research.
De Risio L., Bhatti S. F. M., Muñana K. R., et al. (2015). International Veterinary Epilepsy Task Force consensus proposal: Diagnostic approach to epilepsy in dogs. BMC Veterinary Research.
Berendt M., Farquhar R. G., Mandigers P. J. J., et al. (2015). International Veterinary Epilepsy Task Force consensus report on epilepsy definition, classification and terminology in companion animals. BMC Veterinary Research.
Moore S. A., et al. (2010). Levetiracetam pharmacokinetics in healthy dogs following oral administration. American Journal of Veterinary Research.
Saito M., et al. (2024). Clinical efficacy and tolerability of zonisamide monotherapy in dogs with newly diagnosed idiopathic epilepsy. Frontiers in Veterinary Science.
Rundfeldt C., Löscher W. (2014). The pharmacology of imepitoin. CNS Drugs.
Ruszkiewicz J., & Pinkas A. (2017). Neurotoxic effects of organophosphate and carbamate insecticides: A review. Environmental Toxicology and Pharmacology.
FIDOQUEL-CA1 (Phenobarbital Tablets) Prescribing Information. U.S. FDA.
Note: The information provided in this article is for informational purposes only and should not replace veterinary advice. Always consult with your veterinarian regarding the specific needs and treatment options for your dog with epilepsy.
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