Topiramate: a new antiepileptic drug for refractory epilepsy.

Topiramate is a recently licensed and marketed antiepileptic drug in the UK for use as add-on therapy for refractory partial epilepsy. It has multiple modes of action involving voltage-dependent sodium channels, GABA receptors and glutamate receptors. Topiramate has very favourable pharmacokinetics as it is primarily excreted unchanged. Its metabolism is, however, increased by enzyme inducers, and it can inhibit the metabolism of phenytoin in some patients. Its efficacy as adjunctive treatment in refractory partial epilepsy in adults appears good, over 40% of patients have a 50% or greater reduction in seizure frequency when topiramate is added to their regime with up to 7% becoming seizure free. The main adverse events are ataxia, impaired concentration, confusion, dizziness, fatigue, parasthesia, somnolence and "thinking abnormal'. Most of these occurred during rapid titration. During long-term treatment, weight loss also occurred and nephrolithiasis occurred in 1.5% of patients receiving topiramate. Topiramate is a useful and well-tolerated addition to our treatment of refractory epilepsy, but it should be titrated slowly in order to avoid adverse events.