Acetazolamide for Preventing Acute Mountain Sickness in Healthy Older than 40 years. RCT

Background: Acetazolamide is established for preventing acute mountain sickness (AMS) in young, healthy individuals. We evaluated whether acetazolamide prevents AMS in healthy persons older than 40y, an age group not included in previous studies. Methods: In a randomized, placebo-controlled, double-blind parallel-design trial, 345 healthy lowlanders, mean±SD age 53±7y, 69% women, were treated with acetazolamide capsules (375mg/day) or placebo, starting 24h before ascent to and while staying 2 days at 3100m. Primary outcome: incidence of AMS, i.e., Lake Louise score ≥3 including headache at 3100m. Secondary outcomes: incidence of other altitude-related illnesses, nocturnal pulse oximetry (mean SpO2 and number of SpO2 dips >3%/h as index of periodic breathing), and treatment-related side effects. (ClinicalTrials.gov NCT03561675) Results: Fifty-four of 170 (32%) participants receiving placebo and 38 of 175 (22%) receiving acetazolamide experienced AMS (Chi-Square statistic P=0.035), hazard ratio 0.48, 95%CI, 0.29 to 0.80, number needed to prevent one case of AMS 10 (95%CI, 5 to 141). In participants using placebo, mean nocturnal SpO2 was lower (84.6±0.2%) and SpO2 dips/h were more prevalent (21.7±1.1) compared to participants using acetazolamide (mean difference 3.1% (2.5 to 3.7) and 10.5/h (8.4 to 12.7), P<0.001, both comparisons. Other altitude-related illnesses occurred in 5(3%) using placebo and 3(2%) using acetazolamide (P=0.497). Conclusion: Among healthy lowlanders ≥40 years staying at 3100m, the incidence of AMS was relatively low and further reduced by preventive treatment with acetazolamide. Acetazolamide improved nocturnal oxygenation and stabilized the breathing pattern.