Because it is metabolized differently in dogs, it not as effective in dogs. It also can be toxic to the liver. Phenytoin is toxic to cats and should not be used. It is a very effective anticonvulsant, but is metabolized very quickly in dogs, making it's effects short lasting. It is given in emergency situations because it works quickly.
Acute toxicity includes drowsiness, lethargy, and depression.
Potassium Bromide is used mostly as a secondary anticonvulsant in animals refractory to phenobarbital, however, can be used alone. Due to its lack of metabolism it is the ideal anticonvulsant for patients with liver disease. Acute toxicity includes vomiting, anorexia, constipation, sedation and incoordination. This information was made possible by funds from the Neurology Endowment at Washington State University.