Background: The majority of epileptic patients have a good prognosis and their seizures can be well controlled with the use of a single antiepileptic agent, but up to 30% develop refractory epilepsy, especially those with partial seizures. In this review we summarize the current evidence regarding a new antiepileptic drug, topiramate, when used as an add-on treatment for drug-resistant partial epilepsy.
Objectives: To evaluate the efficacy and tolerability of topiramate when used as an add-on treatment in patients with drug resistant partial epilepsy.
Search strategy: (a) The Cochrane Library (1999 Issue 1); (b) The controlled trial register of the Cochrane Epilepsy Group; (c) Johnson and Johnson, makers of topiramate; (d) Experts in the field.
Selection criteria: Randomized placebo controlled add-on trials of topiramate in patients with drug resistant epilepsy.
Data collection and analysis: Two reviewers independently selected trials for inclusion and extracted the relevant data. The following outcomes were assessed: (a) 50% or greater reduction in seizure frequency; (b) treatment withdrawal (any reason); (c) side effects. Primary analyses were intention to treat. Summary odds ratios (OR) were estimated for each outcome. Dose response was evaluated in regression models.
Main results: Six trials were included representing 743 randomized patients.
Efficacy: Overall OR (95% CIs) for 50% or greater reduction in seizure frequency compared to placebo 4.06 (2.86-5.78). Dose regression analysis shows increasing efficacy with increasing dose, but found no advantage for doses over 400 mg per day. Global effectiveness: treatment withdrawal OR (95% CIs) compared to placebo 2.57 (1.65-4.00). Side effects: OR (99% CIs)compared to placebo, dizziness 1.99 (1.20-3.29); fatigue 2.52 (1. 47-4.32); nausea 2.84 (1.36-5.93); somnolence 2.89 (1.72-4.85) and 'thinking abnormally' 3.71 (2.02-6.80) were significantly associated with topiramate.
Reviewer's conclusions: Topiramate has efficacy as an add-on treatment in patients with drug resistant partial epilepsy. However, trials reviewed were of relatively short duration, and provide no evidence for the long term efficacy of topiramate. Results cannot be extrapolated to monotherapy or patients with other epilepsy types.