Schwartz-Porsche D, et al. Efficacy of Primidone in dogs with seizures unresponsive to Phenobarbital. For Your Dog and Cat. Always discuss any changes regarding your dog's health or medication with your veterinarian. It is the drug of choice for certain types of seizures in people.
Dogs metabolize Phenytoin much faster than people.
It is very difficult to maintain adequate blood levels of this drug in dogs, making it very ineffective for treatment of canine epilepsy. In one clinical study, only 1 of 77 epileptic dogs could be controlled with this drug. PT requires very high doses even to attain minimal blood levels and doesn't reach adequate therapeutic blood levels. It use to be used in combination with phenobarbital and was thought to be effective. There are few side-effects.