Topiramate: a new antiepileptic drug

To review proposed mechanisms of action, clinical pharmacology, efficacy, safety, and tolerability of the antiepileptic drug (AED) topiramate.

All available data from the clinical development program--published and unpublished data (provided by investigators or the RW Johnson Pharmaceutical Research Institute)--were analyzed, with emphasis on the results of double-blind, placebo-controlled trials. Data from open-label studies provided information about long-term efficacy and tolerability.

Topiramate is highly effective in the control of previously therapy-resistant partial seizures, with or without secondary generalization. In the refractory adult patient population enrolled in controlled clinical trials, seizures were reduced by 50% or more in 27-47% of patients compared with 0-18% in placebo-treated patients and by 75% or more in 9-36% of the patients compared with 0-9% of those receiving placebo. The most common adverse effects involve the central nervous system and are mild to moderate in nature. Adverse effects include somnolence, fatigue, psychomotor slowing, and concentration problems. The currently recommended dosing is lower and titration slower than schedules used in the clinical trials; this may improve the tolerability of topiramate. Topiramate has few interactions with currently available AEDs, but phenytoin concentrations increased in some patients. Topiramate can be used initially as adjunctive therapy. Plasma topiramate concentrations are reduced substantially when used with enzyme-inducing AEDs. Open-label data and a single double-blind trial suggest that topiramate monotherapy may be effective. Open-label data also indicate that topiramate may be effective in generalized seizures of nonfocal origin, including those associated with Lennox-Gastaut syndrome.

The robust clinical effects of topiramate expand the therapeutic options for patients with epilepsy. Controlled clinical trials are needed to verify initial observations that topiramate may be effective against a broad spectrum of seizure types and to directly compare efficacy and tolerability with other new and standard AEDs.