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IntroductionNorth American guidelines propose 125 mg acetazolamide twice daily as the recommended prophylactic dose to prevent acute mountain sickness (AMS). To our knowledge, a dose lower than 125 mg twice daily has not been studied.MethodsWe conducted a prospective, double-blind, randomized, noninferiority trial of trekkers to Everest Base Camp in Nepal. Participants received the reduced dose of 62.5 mg twice daily or the standard dose of 125 mg twice daily. Primary outcome was incidence of AMS, and secondary outcomes were severity of AMS and side effects in each group.ResultsSeventy-three participants had sufficient data to be included in the analysis. Overall incidence of AMS was 21 of 38 (55.3%) in reduced-dose and 21 of 35 (60.0%) in standard-dose recipients. The daily incidence rate of AMS was 6.7% (95% CI 2.5-10.9) for each individual in the reduced-dose group and 8.9% (95% CI 4.5-13.3) in the standard-dose group. Overall severity of participants' Lake Louise Score was 1.014 in the reduced-dose group and 0.966 in the standard-dose group (95% CI 0.885-1.144). Side effects were similar between the groups.ConclusionsThe reduced dose of acetazolamide at 62.5 mg twice daily was noninferior to the currently recommended dose of 125 mg twice daily for the prevention of AMS. Low incidence of AMS in the study population may have limited the ability to differentiate the treatment effects. Further research with more participants with greater rates of AMS would further elucidate this reduced dosage for preventing altitude illness.

Original publication





Wilderness & environmental medicine

Publication Date





12 - 21


University of Utah Health, Division of Emergency Medicine, Salt Lake City, UT.


Humans, Pulmonary Edema, Altitude Sickness, Acetazolamide, Carbonic Anhydrase Inhibitors, Double-Blind Method, Mountaineering, Adult, Middle Aged, Female, Male