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.