The long-term safety and efficacy of gabapentin (Neurontin) as add-on therapy in drug-resistant partial epilepsy. The US Gabapentin Study Group.

This is the 2-year interim report of results from a multicenter, open-label study evaluating the long-term efficacy and safety of gabapentin (Neurontin) as add-on therapy in patients with refractory partial seizures who had had a therapeutic response to gabapentin in a preceding 12-week double-blind trial or 12-week open-label extension. A total of 240 patients continued to receive gabapentin as add-on therapy at dosages of 600-2400 mg/day for an average of 342 days (range 10-784 days). Efficacy analyses compared seizure frequency during consecutive 12-week treatment periods with seizure frequency during the 12-week baseline. During the nine treatment periods evaluated, the percent of patients with a 50% or greater reduction in seizure frequency ranged from 35% to 71%, and the median percent change in seizure frequency ranged from -33% to -60%. At the time of data cutoff, 30% of patients had withdrawn from the study due to lack of efficacy, and 4% due to adverse events. In 225 patient-years of gabapentin treatment in this study, CNS adverse events reported by more than 10% of patients were nystagmus, somnolence, diplopia, tremor, ataxia, and dizziness. No consistent changes in clinical laboratory values were associated with gabapentin. Gabapentin as add-on therapy at dosages up to 2400 mg/day is safe during long-term treatment in patients with refractory partial seizures. Subgroup analyses of patients who remained in the study over the long term confirmed that gabapentin maintained efficacy for up to 2 years.