Objective
Acetazolamide is the standard agent of choice for medical prophylaxis against acute mountain sickness (AMS). The current North American guidelines propose 125 mg twice daily (BID) as the recommended prophylactic dose. To our knowledge, a dose lower than 125 mg twice daily has not been studied. We sought to determine whether 62.5 mg twice daily was as effective as 125 mg twice daily for the prevention of AMS. In addition, we sought to measure the number and severity of side effects experienced by users of each dose.
Methods
We conducted a prospective double-blind randomized noninferiority trial of healthy trekkers and climbers traveling to Everest Basecamp in Nepal or those ascending Denali in Alaska. Participants received either the reduced dose of acetazolamide at 62.5 mg twice daily or the standard dose of 125 mg twice daily before and during ascent. Outcome measures included the incidence and severity of AMS in each group as well as the prevalence of common side effects of the medication.
Results
Ninety participants had data sufficient to be included in the analysis. The incidence of AMS did not vary significantly between the 2 groups; the mean Lake Louise Score was 0.966 for the 125 mg BID dose group and 1.014 for the 62.5 mg BID dose group (CI, 0.885–1.144). Side effects experienced by the 62.5 mg BID group were, curiously, slightly higher than those of 125 mg BID dose group, but these differences diminished when controlling for participant weight.
Conclusions
A reduced dose of acetazolamide 62.5 mg BID is as effective as the currently recommended dose of 125 mg BID for the prevention of AMS. These results could influence future recommendations for climbers and trekkers with ascent profiles similar to those seen in our study.