ObjectivesTo evaluate the efficacy and safety of topiramate as an add‐on therapy in dogs with refractory idiopathic epilepsy.MethodProspective, open label, non‐comparative clinical trial of topiramate in dogs with idiopathic epilepsy and poor seizure control despite therapeutic serum concentrations of phenobarbital and potassium bromide. The efficacy of topiramate was evaluated by comparing seizure and seizure day frequencies during a retrospective 2‐month period with a prospective short‐term follow‐up of 6 months. An additional long‐term follow‐up period ranging from 3 to 9 months was conducted on dogs that responded to topiramate therapy during the short‐term follow‐up.ResultsTen dogs were included. Five (50%) responded to topiramate therapy during the short‐term follow‐up showing a significant (P=0·04) decrease of 66% in seizure frequency. Three of the five dogs remained responders during the long‐term follow‐up. Weight loss, sedation and ataxia were the most common adverse effects of topiramate therapy, but in dogs with moderate sedation or ataxia, signs subsided in a few weeks to few months to mild sedation or ataxia.Clinical SignificanceTopiramate may be effective as an add‐on medication in treating canine idiopathic epilepsy. Apart from sedation and ataxia reported in some of the dogs, topiramate was well‐tolerated.