Comparison of phenobarbital and potassium bromide monotherapies in the treatment of canine epilepsy

A one-year clinical trial was conducted to compare phenobarbital and potassium bromide (KBr) monotherapies in the treatment of canine idiopathic epilepsy. The purpose of this research was to investigate which of these two anticonvulsants veterinarians should recommend as the drug of first choice in canine epileptic therapy. Aims of the study were the following: (1) to identify which drug was safer and more effective with fewer associated adverse effects and better seizure control, (2) to determine the incidence and time of onset of adverse effects associated with either drug, and (3) to determine if any risk factors exist for the development of adverse effects with either drug.

The study subjects were 63 client-owned pet dogs with idiopathic epilepsy. The phenobarbital treatment group consisted of 30 dogs, and the KBr treatment group consisted of 33 dogs. After enrolment into the study and initiation of drug therapy, each dog was re-evaluated by their veterinarian at 1, 4 and 12 months of treatment. Data collection occurred prior to the start of the drug (Time 0), and at each of the 3 subsequent veterinary visits. Results from physical examinations, detailed medical and seizure histories, serum biochemical analyses, complete blood count (CBC) analyses and serum drug concentrations were evaluated. Data analysis included comparisons between the two treatment groups with respect to seizure frequency and severity, incidence of adverse effects and results of serum biochemistry and CBC analyses. Correlations between the incidence of adverse effects and signalment variables, drug dosage, serum drug concentration, and length of therapy were also performed within each treatment group.

Results of the study showed that KBr monotherapy was associated with worse seizure control and a higher incidence of adverse effects compared to phenobarbital monotherapy. These adverse effects included lethargy, skin problems, vomiting, pancreatitis, inappropriate defecation and hyperactivity. More dogs in the KBr treatment group failed to complete the study due to poor seizure control or intolerable adverse effects. Phenobarbital therapy was associated with a higher proportion of dogs that developed significant elevations in serum alkaline phosphatase activity. There were no dogs in either group that developed clinical hepatotoxicity. Seizure frequency and severity decreased with increased time of drug therapy for both phenobarbital and KBr. No significant correlations were found between drug dosage, serum drug concentration, or length of therapy and the incidence of adverse effects reported in either drug group.

These results show that phenobarbital should be recommended as the drug of first choice in canine anticonvulsant therapy because it is both safer and more effective. In the cases of epileptic dogs with liver disease, KBr should be prescribed instead as it is not metabolized by the liver and is not reported to cause hepatotoxicity. The results of this study will aid in the development of safer and more appropriate recommendations and guidelines for anticonvulsant therapy in dogs.