Using Zonisamide for Treating Seizures in Dogs and Cats

Learn about Zonisamide, a new anticonvulsant medication

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If your dog or cat has been diagnosed with epilepsy or another seizure disorder, the veterinarian may prescribe an anticonvulsant such as Phenobarbital or potassium bromide. However, if you find your pet is not reacting well to these drugs, there is another option—a relatively new medication called Zonisamide. 

Zonisamide is an anticonvulsant medication that is unrelated to the other anticonvulsants routinely used for treating dogs and cats. Zonisamide can be used alone or in combination with Phenobarbital and/or potassium bromide for treating seizures. This may be useful in cases where your pet's seizures are not adequately controlled by taking Phenobarbital or potassium bromide alone or combined. It may also be a good alternative for animals that are allergic to or have serious side effects from other anti-seizure medications.

Ways to Take Zonisamide

Zonisamide can be used by itself or combined with other anticonvulsant medications. For dogs that cannot tolerate Phenobarbital or potassium bromide, Zonisamide may be a viable option. It may also be an option for dog owners who do not want to risk the side effects of Phenobarbital or potassium bromide for their dog.

Zonisamide levels in the blood can be measured, but there is a lack of agreement among veterinarians regarding whether measurement of blood levels is needed. Some veterinarians believe that measuring is important to evaluate whether the dosage is adequate and is not approaching toxic levels. Others prefer to rely on clinical signs and monitoring of seizure activity to determine the efficacy of the medication dosage for the pet.

Side Effects of Zonisamide

While Zonisamide appears to be relatively safe for dogs, is effective in controlling seizures, and is well-tolerated, many veterinarians are still concerned that we may not know the entire range of side effects possible with the drug because its use has been somewhat limited so far. As with most anticonvulsant drugs, Zonisamide can cause drowsiness, incoordination (loss of muscle control), and a depressed appetite in dogs. It can also cause vomiting, diarrhea, anorexia, and in rare cases, skin reactions, hyperthermia, and blood disorders.

Zonisamide also appears to be relatively safe in cats based on the what we know so far. Zonisamide has had even more limited use in cats than in dogs, though, and some veterinarians worry that we may not be fully aware of the safety profile and potential side effects that may occur using Zonisamide for cats. 

Zonisamide is known to cause birth defects in puppies and kittens and should not be given to pregnant or nursing animals. It should also not be given to animals that are hypersensitive to sulfa drugs.

Administration and Dosage of Zonisamide

Your veterinarian will determine the best method of administration and dosage for your pet, taking into consideration the best outcome and the pet's safety. The most common form of this drug is in a sugar-coated tablet. The average dosage for a dog with epilepsy is 8 to 12 mg/kg administered by mouth every 8 to 12 hours.

Source: Plumb, Donald C. Plumb's Veterinary Drug Handbook, 6th edition. John Wiley and Sons: USA. 2016.