Neuropathic pain (NP) is a severe condition of pain which is followed by tissue injury which leads to nerve dis-functioning. Millions of people worldwide are affected by Neuropathic pain with an estimated 7% in the general population. Amongst many medicines available, Gabapentin is frequently used as a treatment option for NP.

This review was executed by Wiffen PJ et al. to investigate the analgesic efficacy and adverse effects of Gabapentin in adults suffering from chronic NP.  CENTRAL, MEDLINE, and Embase databases were searched for randomised controlled trials from January 2014 to January 2017. Reference lists of retrieved studies and reviews and online clinical trials registries were also considered. The trials of two weeks' duration or longer, comparing Gabapentin (any route of administration) with placebo or another active treatment for NP was inculcated along with the participant-reported pain assessment.

The evaluation of quality, potential bias and extraction of data was done by two review authors independently. The primary outcomes comprised of participants with substantial pain relief or moderate pain relief. Pooled analysis was used to determine the substantial or moderate benefit. The authors used dichotomous data to calculate risk ratio (RR) and number needed to treat for an additional beneficial outcome (NNT) or harmful outcome (NNH) where pooled analysis was feasible. GRADE estimated the quality of the evidence, and thus, a 'Summary of findings' tables was formulated.

Four new studies (530 participants) were included, and three prior included studies (126 participants) were excluded. A total of 37 studies provided information on 5914 participants. In various NP conditions especially postherpetic neuralgia and painful diabetic neuropathy, most of the studies used Gabapentin or Gabapentin encarbil (1200 mg or more daily). The study duration was 4-12 weeks, although not all studies reported significant outcomes of interest. Small size (especially in cross-over studies) and handling of data after study withdrawal gave way to high risk of bias.

In case of postherpetic neuralgia, more participants (32%) had a substantial benefit (at least 50% pain relief or PGIC very much improved) with Gabapentin 1200 mg daily or greater than with placebo (17%) and NNT 6.7 (5.4 to 8.7). In almost 46% participants, moderate benefit (at least 30% pain relief or PGIC much or very much improved) with Gabapentin 1200 mg daily or greater than with placebo (25%) and NNT 4.8 (4.1 to 6.0) was observed.

In case of painful diabetic neuropathy, more participants (38%) had a substantial benefit (at least 50% pain relief or PGIC very much improved) with Gabapentin 1200 mg daily or greater than with placebo (21%) and NNT 5.9 (4.6 to 8.3). In 52% participants, moderate benefit (at least 30% pain relief or PGIC much or very much improved) with Gabapentin 1200 mg daily or greater than with placebo (37%) and NNT 6.6 (4.9 to 9.9) was observed.

Adverse event withdrawals were more frequent with Gabapentin (11%) than with placebo (8.2%) and NNH 30 (20 to 65) in case of all conditions combined. Serious adverse events were no more common with Gabapentin (3.2%) than with placebo; there were eight deaths. Dizziness (19%), somnolence (14%), peripheral oedema (7%), and gait disturbance (14%) were seen in participants taking Gabapentin.

Overall results confirm that 1800mg–3600mg dosage of Gabapentin may effectively provide pain relief in postherpetic neuralgia and peripheral diabetic neuropathy patients. However, pieces of evidence for other kinds of neuropathic pain is limited. At least 50% pain intensity reduction is regarded as a significant outcome of treatment by patients as it is concerned with some crucial beneficial effects on sleep interference, fatigue, depression, quality of life (QoL), function and work. Out of 10 patients, 3-4 patients showed this degree of pain relief with Gabapentin. This rate was higher than that of the placebo group in which 1 or 2 out of 10 got relief from NP. However, half of the patients from Gabapentin group did not get pain relief though they may experience adverse events.