Treatment of canine epilepsy with primidone

Forty-seven dogs with a history of generalized recurrent seizures were treated with primidone at a daily oral dosage of 13 to 100 mg/kg of body weight, divided into 2 to 3 doses. During treatment, plasma concentrations of primidone and its metabolites, phenobarbital and phenylethylmalonamide, were determined at irregular intervals. Of the 30 dogs that finally could be evaluated, 20 were brought to excellent or good control of their seizures by daily primidone dosages ranging from 13 to 17 mg/kg and at plasma phenobarbital concentrations of 6 to 37 micrograms/ml. Of the other 10 dogs, 5 improved to a minor extent and 5 did not improve at all. It was concluded that treatment of seizures should start with a daily dosage of 10 to 15 mg/kg, with the dosage being increased to about 35 mg/kg within a few weeks. For dogs in which the seizures are not controlled by this dosage, a further increase should be tried until a plasma phenobarbital concentration of 30 to 40 micrograms/ml is reached or until signs of drug toxicosis develop. Monitoring of plasma phenobarbital concentrations is sufficient for the control of treatment with primidone.