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Objective To assess whether there is a change in seizure activity in dogs with refractory epilepsy that are receiving appropriate doses of phenobarbitone and/or potassium bromide, when gabapentin is added to the therapeutic regimen.

Design A prospective study of 17 dogs with a refractory seizure disorder, 16 of which have idiopathic epilepsy.

Procedure Patients were stabilised using phenobarbitone and/or potassium bromide to produce tolerable therapeutic serum concentrations and dosed additionally with gabapentin at 35 to 50 mg/kg/d (divided twice or three times daily) for 4 months. Owners recorded seizure activity and side effects during this period in a standardised diary. Patients underwent monthly physical examinations and venepuncture to assess selected serum biochemical analytes, as well as phenobarbitone and bromide concentrations. Patients were further monitored for long-term response to adjunctive gabapentin therapy.

Results There was no significant decrease in the number of seizures over the study period for the entire cohort, however three dogs stopped seizuring completely. There was a significant increase in the number of patients who showed an increase in the interictal period (P < 0.001). Serum alkaline phosphatase activity and triglyceride concentrations were elevated at baseline. There were no significant changes in biochemical analytes during the course of the study period. Side effects observed initially on addition of gabapentin included sedation and hind limb ataxia. The former resolved spontaneously after a few days; the latter after a slight reduction in bromide dose. Long-term, a further two patients became seizure free and ten patients remained on gabapentin indefinitely. No long-term side effects have become apparent.

Conclusion Addition of gabapentin to phenobarbitone and/or potassium bromide increased the interictal period and shortened the post-seizure recovery in some canine epileptics. In some dogs, seizures were prevented completely, while in others there was an increase in interictal period. The short-half life of gabapentin has advantages for seizure control, however its present high cost may prohibit therapy in large dogs.