Bottom Line
There is no good evidence to support or contradict the suggestion that gabapentin at daily doses of 1200 to 2400 mg reduces pain in fibromyalgia.
Background
Fibromyalgia is a complex disorder characterised by widespread pain, fatigue, poor sleep, low mood, and other bodily symptoms. Common pain-relieving medicines such as paracetamol and ibuprofen are not usually considered effective. Antiepileptic drugs are commonly used to treat fibromyalgia, but there is uncertainty about how good they are.
Gabapentin is a medicine used to treat pain caused by nerves that are not working properly. Gabapentin changes the way that the nerves send messages to the brain. It can be taken in a tablet or a liquid, with or without food. Doses are usually 1200 mg to 2400 mg each day. At the start of treatment low doses are used to minimise side effects, but the dose is usually increased after a few weeks.
Study characteristics
In May 2016 we searched for clinical trials where gabapentin was used to treat pain due to fibromyalgia in adults. We found one study that met the requirements for this review. The study tested 1200 to 2400 mg/day of gabapentin compared with a placebo over 12 weeks, in 150 people.
Key results
The study did not report the number of people with pain reduced by half at the end of week 12. At that time 5 in 10 people taking gabapentin and 3 in 10 taking the placebo had their pain reduced by at least one third. A report of feeling better to any degree was reported by 9 in 10 taking gabapentin and 5 in 10 taking placebo.
About 2 in 10 people taking gabapentin stopped taking the medicine because of side effects, compared with 1 in 10 taking the placebo. The study did not report the number of people with serious side effects, but did report that there were no deaths.
Quality of the evidence
We rated the quality of the evidence as very low because there was only a single small study with important study limitations. Several factors reduced our confidence in the result. Very low quality evidence means that we are very uncertain about the results.
We have only very low quality evidence and are very uncertain about estimates of benefit and harm because of a small amount of data from a single trial. There is insufficient evidence to support or refute the suggestion that gabapentin reduces pain in fibromyalgia.
This review replaces part of an earlier review that evaluated gabapentin for both neuropathic pain and fibromyalgia, now split into separate reviews for the two conditions. This review will consider pain in fibromyalgia only.
Fibromyalgia is associated with widespread pain lasting longer than three months, and is frequently associated with symptoms such as poor sleep, fatigue, depression, and reduced quality of life. Fibromyalgia is more common in women.
Gabapentin is an antiepileptic drug widely licensed for treatment of neuropathic pain. It is not licensed for the treatment of fibromyalgia, but is commonly used because fibromyalgia can respond to the same medicines as neuropathic pain.
To assess the analgesic efficacy of gabapentin for fibromyalgia pain in adults and the adverse events associated with its use in clinical trials.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online, MEDLINE via Ovid and Embase via Ovid from inception to 24 May 2016. We also searched the reference lists of retrieved studies and reviews, and searched online clinical trial registries.
Randomised, double-blind trials of eight weeks' duration or longer for treating fibromyalgia pain in adults, comparing gabapentin with placebo or an active comparator.
Two independent review authors extracted data and assessed trial quality and risk of bias. We planned to use dichotomous data to calculate risk ratio and number needed to treat for one additional event, using standard methods. We assessed the evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation) and created a 'Summary of findings' table.
Two studies tested gabapentin to treat fibromyalgia pain. One was identified in previous versions of the review and is included here. We identified another study as a conference abstract, with insufficient detail to determine eligibility for inclusion; it is awaiting assessment. The one included study of 150 participants was a 12-week, multi-centre, randomised, double-blind, placebo-controlled, parallel-group study using last-observation-carried-forward imputation for withdrawals. The maximum dose was 2400 mg daily. The overall risk of bias was low, except for attrition bias.
At the end of the trial, the outcome of 50% reduction in pain over baseline was not reported. The outcome of 30% or greater reduction in pain over baseline was achieved by 38/75 participants (49%) with gabapentin compared with 23/75 (31%) with placebo (very low quality). A patient global impression of change any category of "better" was achieved by 68/75 (91%) with gabapentin and 35/75 (47%) with placebo (very low quality).
Nineteen participants discontinued the study because of adverse events: 12 in the gabapentin group (16%) and 7 in the placebo group (9%) (very low quality). The number of serious adverse events were not reported, and no deaths were reported (very low quality).