Epileptic seizure frequency and semiology in dogs with idiopathic epilepsy after initiation of imepitoin or phenobarbital monotherapy.

The aim of this study was to evaluate changes in epileptic seizures (ES) frequency and semiology in antiepileptic-medication (AEM)-naïve dogs with idiopathic epilepsy (DIE) after initiation of imepitoin (IMP) or phenobarbital (PB) monotherapy. In this observational prospective cohort study, inclusion criteria were as follows: diagnosis of idiopathic epilepsy (based on clinical, laboratory and magnetic resonance imaging investigations) in AEM-naïve dogs and presence of a detailed ES-diary. Exclusion criteria were: occurrence of cluster seizures (CS) or status epilepticus (SE) prior to treatment initiation and concurrent disease and/or treatments. Thirty-one DIE commenced IMP at 10-20mg/kg/12h and 30 dogs commenced PB at 2.50-3.30mg/kg/12h. AEM dosage was increased over time (up to IMP 30mg/kg/12h and PB 5.20mg/kg/12h). All dogs experienced generalised-tonic-clonic ES. In the IMP-group, pre-treatment median ES-frequency was 1.50ES/month (range, 1-4ES/month); post-treatment median ES-frequency was 0.95ES/m (range, 1ES/6m-3ES/m); n=21/31 (67.70%) dogs developed CS 1-18 months after initiation of treatment; n=7/31 (22.60%) dogs experienced unacceptable adverse events in the first month of treatment which required switching to an alternative AEM; and n=3/31(9.70%) dogs did not develop CS with a 3year follow-up. In the PB-group, pre-treatment median ES-frequency was 2.46ES/month (range, 1-7ES/month); post-treatment median ES-frequency was 0.36ES/month (range, 0ES/3years-1ES/month); n=11/30 (36.70%) dogs developed CS between 12-25 months after initiation of treatment. Nineteen of 30 (63.30%) dogs did not develop CS with a 3-year follow-up; three of these 19 dogs were ES free. In this study, AEM-naïve DIE receiving imepitoin-monotherapy developed CS significantly more frequently and earlier in the course of the disease, and developed aggression and required earlier discontinuation of monotherapy than AEM-naïve DIE receiving phenobarbital-monotherapy.