EDITOR—Dumont et al reach a false, potentially harmful conclusion in their paper on the efficacy and harm of pharmacological prevention of acute mountain sickness.1 Their claim that acetazolamide 500 mg/day does not work in preventing acute mountain sickness must be challenged. Their analysis is flawed for three reasons.

Firstly, they used only nine of 25 available controlled studies, and analysed only four of 10 trials with acetazolamide 500 mg/day. Consequently, only 143 individuals taking acetazolamide 500 mg/day were included, 120 from one study.2 In that investigation the rate of ascent in one of the two trials was so slow that acetazolamide made no difference in acute mountain sickness scores. The other trial, with faster rate of ascent, showed acetazolamide to be very effective. Another meta-analysis, of 10 trials of acetazolamide 500 mg/day (306 participants), concluded that it was effective.3 If Dumont et al included more trials they would find that acetazolamide 500 mg/day is indeed effective.

Secondly, rate of ascent was not adequately controlled. The authors compared acetazolamide 750 mg/day (250 mg three times a day) during particularly rapid ascent with 500 mg/day with much slower ascent. If the 500 mg dose is not tested during an abrupt ascent similar to that by the group taking the 750 mg dose the comparison is not valid.

Thirdly, Dumont et al chose an unnecessarily strict end point for their analysis: the dichotomous presence or absence of acute mountain sickness. Many people with symptoms of acute mountain sickness, while not meeting criteria for acute …