Therapeutic efficacy of phenobarbital and primidone in canine epilepsy: a comparison

The efficacy of phenobarbital and primidone against canine epilepsy was compared in a controlled study. Thirty-five dogs showing generalized tonic-clonic seizures (grand mal), treated for a minimum of 6 months, were included in the study; fifteen of these were treated with phenobarbital, the other twenty with primidone. Both drugs were dosed according to the clinical requirement; the daily doses ranged from 5-17 mg/kg phenobarbital and from 17-70 mg/kg primidone. The plasma concentrations of phenobarbital, or of primidone and its metabolites phenobarbital and phenylethylmalondiamide (PEMA), were routinely monitored. Complete control of tonic-clonic seizures for 6 months, at least, was attained in six out of fifteen dogs of the phenobarbital group, and in five out of twenty dogs in the primidone group. A further six dogs on phenobarbital, and seven dogs on primidone, were classified as 'improved', i.e. the rate of seizures was reduced by at least 50%. The rest of the dogs were not improved by the treatment. The difference between the efficacy of phenobarbital and primidone was not significant, but primidone gave rise to signs of liver toxicity in fourteen out of twenty dogs, as indicated by considerable elevations of liver enzyme values (alanine transferase, glutamate dehydrogenase, alkaline phosphatase). Phenobarbital is, therefore, regarded as the drug of first choice for the treatment of canine epilepsy.