Zonisamide, originally introduced in the United States in 2000 to treat human seizures, is a newer class of drug therapy approved for use in canines for control of both focal and generalized seizures, according to DVM Newsmagazine. The National Institute of Health states that zonisamide—classified as a sulfonamide-based anticonvulsant—works by decreasing abnormal electrical activity in the brain that leads to seizures. Used either as an add-on or as a stand-alone drug, zonisamide gained significant popularity in 2009 for the treatment of canine refractory epilepsy, said Karen R. Muñana, DVM, MS, DACVIM (neurology), in her July 1, 2009, DVM Newsmagazine article, "Newer options for medically managing refractory canine epilepsy."
Antiseizure drugs introduced within the past 15 years, including gabapentin, felbamate, zonisamide and levitiracetam, have fewer side effects than the standard drugs, phenobarbital and potassium bromide, according to Johnny D. Hoskins, DVM, PhD, Dipl. ACVIM, in DVM Newsmagazine's Mar. 1, 2008, article, "New anticonvulsant drugs show promise in dogs, cats."
"These drugs are being considered more frequently as first-line anticonvulsant therapy for canine epilepsy," said Dr. Hoskins.
Zonasimide Gains Popularity as a Medication for Canine Epilepsy
With fewer side effects than more traditional anticonvulsant drugs, zonisamide is quickly gaining traction as a safe, viable and efficacious option for treating persistent cases of idiopathic epilepsy in canines. The drug works by blocking T-type calcium and voltage-gated sodium channels in the brain, facilitating dopaminergic and serotonergic neurotransmission, scavagenging free-radicals, enhancing activity of the class of receptors that interact with the neurotransmitter gamma-aminobutyric acid (GABA) and decreasing glutamate-mediated processes, according to Dr. Hoskins.
Like many other anticonvulsants, zonisamide is metabolized by the liver. It has been widely used both as a complement and as a sole antiepileptic drug in dogs not adequately treated by more traditionally-used drug therapies, according to the Merck Veterinary Manual.
While more costly than traditional antiseizure drug therapies, zonisamide has mild side effects, when compared to other therapies. Common side effects of zonisamide are drowsiness, ataxia, loss of appetite and gastrointestinal upset, although no serious adverse effects have been reported, the Journal states.
Zonisamide remains an increasingly safe and popular option, either as an add-on or as a stand-alone tool, for controlling seizures in canines. A prospective study published in the July/August 2004 issue of the Journal of the American Animal Hospital Association determined that most canines with refractory epilepsy despite adequate blood serum levels of phenobarbitol and/or potassium bromide experienced an 81 percent reduction in seizure activity under the treatment of zonisamide.
Join the Conversation