Gabapentin ineffective for chronic pelvic pain in women

A daily dose of gabapentin does not appear effective in reducing chronic pelvic pain in women, according to results of the GaPP2 study from the UK.

“Women with chronic pelvic pain and no obvious pelvic pathology should be advised that gabapentin might not alleviate their pain and could give them unpleasant side-effects,” noted the researchers.

The 306 women in this multicentre, double-blind study were aged 18–50 years with chronic (≥3 months) pelvic pain despite no obvious pelvic pathology on laparoscopy. They were randomized 1:1 to receive oral gabapentin (titrated to maximum 2,700 mg/day; mean age 30.5 years) or placebo (mean age 30.1 years) for 16 weeks. Pain scores were collected weekly, with reporting of pain at multiple timepoints the prior week.

At week 13–16, worst pain score was comparable between women in the gabapentin and placebo groups (mean numerical rating scale [NRS] score 7.1 vs 7.4). The change in pain scores from baseline did not significantly differ between women in the gabapentin and placebo groups (mean -1.4 vs -1.2; adjusted mean difference, -0.20, 97.5 percent confidence interval [CI], -0.81 to 0.42; p=0.47). [Lancet 2020;396:909-917]

The mean average NRS pain score at week 13–16 was 4.3 and 4.5 in the gabapentin and placebo groups, respectively, with a comparable change from baseline between groups (mean -1.1 vs -0.9; adjusted mean difference, -0.18, 97.5 percent CI, -0.71 to 0.35; p=0.45).

Serious adverse events (AEs) occurred in a greater proportion of gabapentin than placebo recipients (7 percent vs 2 percent; p=0.04). Dizziness, drowsiness, and visual disturbances – known effects of gabapentin – occurred more commonly with gabapentin than placebo (54 percent vs 28 percent; risk ratio [RR], 1.91; p=0.0002 [dizziness]; 52 percent vs 29 percent; RR, 1.71; p=0.002 [drowsiness]; 22 percent vs 11 percent; RR, 2.25; p=0.01 [visual disturbances]).

While chronic pelvic pain can be caused by conditions such as endometriosis, the cause of the condition is often unidentifiable during laparoscopy, said the researchers. Furthermore, no treatments are available for chronic pelvic pain within the gynaecology setting, though there are options available if the cause is non-gynaecological.

This study was adequately powered and there was no evidence of a minimal clinically important difference between treatment groups.

“We have been prescribing this drug for many years with little evidence of its effectiveness. As a result of our study, we can confidently conclude that gabapentin is not effective for chronic pelvic pain in women where no cause has been identified,” said lead researcher Professor Andrew Horne from the MRC Centre for Reproductive Health, University of Edinburgh, UK. He called for further research into identifying other therapies that could potentially be useful for this condition.

“Given the increasing reports of abuse and evidence of potential harms associated with gabapentin use, it is important that clinicians consider alternative treatment options to off-label gabapentin for the management of chronic pelvic pain and no obvious pelvic pathology,” said Horne and co-authors.

“In our opinion, no further research is required to establish the role of gabapentin in the management of chronic pelvic pain in women with no obvious pelvic pathology,” the researchers continued. However, it remains a possibility that some women may benefit from gabapentin treatment, a theory that calls for further research.