Abstract

ObjectiveTo evaluate the P2X3 receptor antagonist, gefapixant, for treating moderate-to-severe endometriosis-related pain. DesignRandomized, double-blind, Phase 2, proof-of-concept trial. ParticipantsPremenopausal women age 18-49y with moderate-to-severe endometriosis-related pain who were not using hormonal treatment. InterventionsGefapixant 45mg twice-daily or placebo over two menstrual cycles. Main outcome measuresParticipants rated peak pelvic pain severity daily on a 0 (no pain) - 10 (extremely severe pain) scale. The primary endpoint was change-from-baseline in average daily peak pelvic pain severity during Treatment Cycle 2. ResultsAll 187 participants randomized (gefapixant N=94, placebo N=93) took ≥1 dose of investigational treatment and all but 6 in each treatment group completed the trial. The model-based least squares mean reduction-from-baseline in average daily peak pelvic pain severity during Treatment Cycle 2 was -2.2 for gefapixant and -1.7 for placebo (difference = -0.5 [95% confidence interval: -1.01, 0.03], P=0.066). In secondary analyses, the difference between gefapixant and placebo in peak pelvic pain severity reduction-from-baseline on menstrual days was -0.6 [95% confidence interval: -1.18, -0.06], and -0.5 [95% confidence interval: -1.04, 0.03] on non-menstrual days. Taste-related adverse events were reported in 31.9% of participants for gefapixant versus 4.3% for placebo. Pharmacokinetic assessments at Month 1 and Month 2 clinic visits indicated that of the 94 participants in the gefapixant group, 39 had detectable levels of gefapixant in the blood for both assessments while 38 had no detectable levels for ≥1 assessment. ConclusionGefapixant 45mg twice-daily was not shown to be superior to placebo in reducing endometriosis-related pain, although the results directionally favored gefapixant. This trial result should be considered inconclusive given possible issues with treatment compliance. (Clinical trial registration: NCT03654326)

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