Prochlorperazine maleate versus placebo for the prophylaxis of acute mountain sickness: a double-blind randomized controlled trial.

Background: Acute mountain sickness (AMS) is a debilitating condition that may occur on ascent to high altitude, with limited options for chemoprophylaxis. The pathophysiology of AMS is poorly understood, though it may be similar to migraine. This study aimed to determine the efficacy of prochlorperazine, a first-line agent for acute migraine, for AMS prophylaxis.

Methods: We performed a randomized, double-blind, placebo-controlled trial involving healthy, unacclimatized adult participants, primarily from the Denver area (1609 m), who received either oral prochlorperazine or placebo three times daily for 24 hours during rapid ascent to Mount Blue Sky, Colorado (4348 m). We evaluated individuals who received at least the first dose of placebo or intervention following a modified intent-to-treat approach. Participants travelled by vehicle to 3910 m, then hiked to the summit of Mount Blue Sky, where they slept overnight. The primary outcome was AMS incidence as defined by the 2018 Lake Louise Questionnaire, which was assessed on the evening of ascent and the following morning.

Results: We analysed 56 participants (25 women), with a mean age of 39 [IQR 28-49], with 28 participants in each study arm. Key baseline characteristics were equally distributed and well-matched between study arms. The incidence of AMS was 28 (50%), with 18 (64%) in the placebo arm and 10 (36%) in the prochlorperazine arm (P = 0.06). The absolute risk reduction was 28.6%, the number needed to treat was 4 and the odds ratio was 0.28 (95% C.I. 0.11-0.94). There were no serious adverse events, and there were no significant differences in the side effects between arms, including for drowsiness (P = 0.47).

Conclusion: Our results suggest that prochlorperazine is effective in preventing AMS. Larger studies are warranted to validate our findings.