Zonisamide (brand name: Zonegran®) is an anticonvulsant (antiseizure) medication that is either used as an initial therapy for epilepsy or as an add-on drug for difficult to control seizures. Its use in cat and dogs to treat seizures is 'off label' or 'extra label'.
Zonisamide is a newer effective anticonvulsant medication. It is a safe drug that has few side effects. The drug is well tolerated and is given twice a day. The most common side effect is a transient sedation at the beginning of the treatment. Although metabolized by the liver, hepatotoxicity has not been reported and there is no increment of the liver enzymes. We do not usually see the increase in thirst and appetite as we do with phenobarbital and bromide.
The dose should be higher when zonisamide is used with phenobarbital. Over the years, the generic form has become more affordable, even for larger dogs.
It is the drug of choice when the side effects seen with the previous anticonvulsant drugs are of concern for the pets and the client.