Acetazolamide for the prophylaxis of acute mountain sickness

In 2000, a systematic review concluded that when ascending rapidly to above 4000 m, prophylactic dexamethasone 8-16 mg daily or acetazolamide 750 mg daily both reduced acute mountain sickness.1 However, acetazolamide 500 mg daily was not found be effective. At the time, many doctors who specialise in high altitude sickness thought that this did not reflect their clinical experience, and there were concerns about incomplete inclusion criteria, inadequate control of ascent rates, and unduly strict endpoints.2 3 In a linked systematic review and meta-analysis (doi:10.1136/bmj.e6779), Low and colleagues look at the important question of the efficacy of acetazolamide at lower doses to prevent acute mountain sickness above 3000 m.4 They found that acetazolamide 250 mg and 500 mg daily were both effective in reducing the severity of acute mountain sickness. The different altitudes studied (3000 v 4000 m) could have led to differences in the incidence and severity of acute mountain sickness and may partly account for the studies’ different conclusions.1 4 More people are travelling to high altitude for work (soldiers, miners, construction workers, and astronomers) or recreation (skiing, trekking, mountain biking, and mountaineering). On ascent to altitude, several adaptive physiological processes occur (including hyperventilation, erythropoiesis, and increased cardiac output), all of which tend to increase convective oxygen transport to the tissues, a process termed “acclimatisation.”5