If your dog or cat was diagnosed with epilepsy or another seizure disorder, your veterinarian may prescribe a drug called an anticonvulsant to reduce the frequency of their signs. Traditional anticonvulsants include phenobarbital, levetiracetam, or potassium bromide. While these drugs are effective in treating seizures, they can cause unwanted side effects. There are also restrictions based on species or the presence of concurrent diseases (e.g. potassium bromide is not recommended in cats due to causing airway disease). An alternative anticonvulsant option with few side effects is zonisamide.
Zonisamide is an anticonvulsant medication unrelated to other anticonvulsants routinely used for treating dogs and cats. Zonisamide can be used alone or in combination with phenobarbital and/or potassium bromide. This is useful when your pet's seizures are inadequately controlled with those drugs.
Ways to Take Zonisamide
Zonisamide can be used by itself or combined with other anticonvulsant medications. Traditional antiseizure drugs can cause side effects including sedation, restlessness, loss of coordination, changes in thirst and appetite, or increased urination, among many other issues. For pets that cannot tolerate these drugs, or for pet owners who do not want to risk the side effects, zonisamide may be a viable option.
Pets receiving phenobarbital or potassium bromide must also have blood levels of these drugs measured to ensure they are receiving the appropriate dose. With zonisamide, measurement of blood levels may be needed to evaluate whether the dosage is adequate and not approaching toxic levels. Monitoring of seizure activity to determine the efficacy of the medication dosage for the pet is important.
Side Effects of Zonisamide
While zonisamide appears to be relatively safe for dogs, is effective in controlling seizures, and is well-tolerated, there is research lacking in the clinical efficacy. 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, loss of appetite, and in rare cases, skin reactions and liver problems.
Zonisamide should not be given to pregnant or nursing animals. It should also not be given to animals that are sensitive to sulfa drugs.
Administration and Dosage of Zonisamide
Your veterinarian will determine the best method of administration and dosage for your dog, taking into consideration the best outcome and your 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 5 to 10 mg/kg administered by mouth every 12 hours.
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Podell, M., et al. 2015 ACVIM small animal consensus statement on seizure management in dogs. Journal of Veterinary Internal Medicine. 2016;30(2):477–90. doi:10.1111/jvim.13841
Maintenance Anticonvulsant or Antiepileptic Therapy. Merck Manual Veterinary Manual.
Phenobarbital. VCA Hospitals.
Bromides. VCA Hospitals.
Zonisamide. VCA Hospitals.
Seizure and Anticonvulsant Medications Grid. University of Illinois College of Veterinary Medicine.