Gabapentin as add-on therapy in refractory partial epilepsy: a double-blind, placebo-controlled, parallel-group study. The US Gabapentin Study Group No. 5.

Gabapentin, administered as add-on therapy, was safe and effective in this 12-week, multicenter, placebo-controlled, parallel-group study in 306 patients with refractory partial epilepsy. For patients in each gabapentin treatment group (600, 1,200, or 1,800 mg/d), the mean response ratio was significantly better than that of a placebo group. The percentage of patients achieving at least a 50% reduction in seizure frequency was 8% among placebo-treated patients and ranged from 18% to 26% for patients who received gabapentin. Adverse events were generally mild and transient and occurred at a slightly higher frequency among patients receiving gabapentin than among those receiving placebo. Gabapentin did not affect the serum concentrations of concurrent antiepileptic drugs and was not regularly associated with any deviations in clinical laboratory values. Gabapentin's low inherent toxicity and its lack of drug interactions make it an ideal candidate for use as add-on therapy in patients with refractory partial epilepsy.