Zonisamide resides in the class of of medications known as anti-convulsants, which are used to treat seizures and other abnormal electrical activity in the brain in the form of a mood stabilizer. The drug was approved for human use in 2000. Its use in canines has been undergoing studies.
Research thus far has concluded that it is effective as an add-on therapy for dogs with refractory epilepsy, preventing seizures, however there is a significant chance of unwanted side effects. Refractory epilepsy in dogs lacking of a sufficient response to potassium bromide and phenobarbital treatment are the primary candidates for zonisamide use. The half-life in dogs, according to the Department of Small Animal Medicine and Surgery, is around 15 hours. The majority of Zonisamide is excreted through urine, and small amounts through hepatic metabolism.
Zonisamide works by reducing pre-synaptic glutamate release. It blocks electrical activity in the sodium and calcium channels within the brain. An increase in neurotransmitter levels of dopamine and serotonin have also been found in the striatal and hippocampal parts of the brain.
With canine use, the drug has so far appeared to be somewhat safe with minimal side effects recorded in dogs. Mild ataxia and sedation, vomiting, apparent nausea, and loss of appetite was reported in some dogs in studies conducted in 2004. In dogs, zonisamide may cause binding of tissues to the eye resulting in possible vision problems.
The recommended dosage in dogs is 5 to 10mg/kg twice daily. A serum concentration of 10-40 ug/ml is what most veterinarians recommend as an effective and safe dose. Doses up to four times the recommended dosage caused slight changed in blood count and an increase in the weight of the liver were observed in a study in 1988. These studies involved both dogs and rats.
Studies still have limited information and data with the use of zonisamide as an anti-convulsant in dogs, but available research continues to show its effectiveness in use on dogs with refractory epilepsy. The studies that have been conducted show roughly a 50% decrease in the seizure activity of canines when used in combination with phenobarbital. Zonisamide resulted in an impairment of seizure control in one specific study of dogs (Hamada, K., Song, H.K., Ishida, S., Yagi, K., Seino, M. (2001) Contrasting effects of zonisamide and acetazolamide on amygdaloid kindling rats, Epilepsia 42, 1379-1386).
Risk factors for dogs and humans alike include kidney stones, blood disorders, liver problems, and breastfeeding. Zonisamide should not be used on pregnant dogs. Sudden stopping of the use of zonisamide is dangerous and may lead to a rapid increase in severe seizures. Most major side effects are extremely rare, but it is highly recommended you talk to a professional veterinarian about all the possible side effects in your dog.