N-of-1 randomized trials to assess the efficacy of gabapentin for chronic neuropathic pain.

OBJECTIVE The objective of this study was to compare the efficacy of gabapentin with placebo for neuropathic pain at the individual and population levels. DESIGN This study used an n-of-1 trial methodology with three double-blind, randomized, crossover comparisons of gabapentin with placebo. SETTING This study was carried out at specialist outpatient clinics at two Australian hospitals. Patients. The patients are adults with chronic neuropathic pain. INTERVENTIONS Following a dose-finding period, participants underwent three comparisons of 2-week periods on gabapentin (600-1,800 mg per day) and placebo. The dose-finding period was commenced by 112 patients, of whom 39 had no response so they did not enroll, leaving 73 trial participants. Of these, 48 completed and 7 partially completed their trials, and 18 withdrew. OUTCOME MEASURES The five outcome measures were the visual analog scale (0-10) of pain, sleep interference and functional limitation; frequency of adverse events and medication preference. The aggregate response was determined by weighting the response to each measure equally. RESULTS Of the 55 participants who completed at least one cycle, the aggregate response to gabapentin was better than placebo in 16 (29%), of whom 15 continued gabapentin posttrial. No difference was shown in 38 (69%), and 1 (2%) showed a better response to placebo. Fifteen of these 39 continued gabapentin posttrial. Meta-analysis of the mean scores showed lower mean (standard deviation) scores for gabapentin by 0.8 (0.2) for pain, 0.6 (0.2) for sleep interference, and 0.6 (0.2) for functional limitation. CONCLUSIONS The response rate and mean reduction in symptoms with gabapentin were small. Gabapentin prescribing posttrial was significantly influenced by the trial results.