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.