Gabapentin is equal to placebo for pain relief in women with chronic pelvic pain (GaPP2), but with more side effects

Référence

Horne AW, Vincent K, Hewitt CA, et al, for the GaPP2 collaborative. Gabapentin for chronic pelvic pain in women (GaPP2): a multicentre, randomised, double-blind, placebo-controlled trial. Lancet 2020;396(10255):909-917.

Sommaire

This study took place in 39 hospital centers in the United Kingdom and included 306 women, 18 years to 50 years of age, who had chronic pelvic pain (as defined by the Royal College of Obstetricians and Gynaecologists and the 2012 International Association for the Study of Pain taxonomy) for at least 3 months. The women also had to have no obvious pathology during the laparoscopies that had to be performed between 2 weeks and 3 years of enrollment. Among the many exclusions, the authors excluded women who only had dysmenorrhea. Before randomization, each eligible woman entered a 4-week screening phase during which they were asked to record their worst and average pain levels (on a 10-point scale) for each week. To be randomized, the women had to record at least 3 of the 4 weekly ratings to show adherence to data collection, and at least 2 of the worst scores had to be 4 out of 10 or higher. In the past, I have railed about how active run-in periods stack the deck in favor of interventions. Additionally, inactive run-ins stack the deck in favor of adherent patients who may not look like those we see in practice. As you will see, this strengthens the conclusions of this study. The dosing regimen for gabapentin started at 300 mg daily and the dose was increased by one capsule every 3 days until the woman experienced adequate pain relief, could not tolerate side effects, or reached a maximum of 9 capsules. At the end of 4 months, the researchers had pain data on approximately 80% of the women and imputed the data for the remainder. At the end of the study, the average pain scores and worst pain scores declined for women in both groups, but the net differences were nearly identical. However, the women who took gabapentin were much more likely to experience dizziness (54% vs 28%) or drowsiness (52% vs 29%). The study was large enough to detect a 1-point difference on the 10-point pain scale.