Acetazolamide prevents acute mountain sickness (AMS) by inhibition of carbonic anhydrase. Since it also reduces acute hypoxic pulmonary vasoconstriction (HPV), it may also prevent high-altitude pulmonary edema (HAPE) by lowering pulmonary artery pressure. We tested this hypothesis in a randomized, placebo-controlled, double-blind study. Thirteen healthy, nonacclimatized lowlanders with a history of HAPE ascended (<22 h) from 1,130 to 4,559 m with one overnight stay at 3,611 m. Medications were started 48 h before ascent (acetazolamide: n = 7, 250 mg 3 times/day; placebo: n = 6, 3 times/day). HAPE was diagnosed by chest radiography and pulmonary artery pressure by measurement of right ventricular to atrial pressure gradient (RVPG) by transthoracic echocardiography. AMS was evaluated with the Lake Louise Score (LLS) and AMS-C score. The incidence of HAPE was 43% versus 67% (acetazolamide vs. placebo, P = 0.39). Ascent to altitude increased RVPG from 20 ± 5 to 43 ± 10 mmHg (P < 0.001) without a group difference (P = 0.68). Arterial Po2 fell to 36 ± 9 mmHg (P < 0.001) and was 8.5 mmHg higher with acetazolamide at high altitude (P = 0.025). At high altitude, the LLS and AMS-C score remained lower in those taking acetazolamide (both P < 0.05). Although acetazolamide reduced HAPE incidence by 35%, this effect was not statistically significant, and was considerably less than reductions of about 70%-100% with prophylactic dexamethasone, tadalafil, and nifedipine performed with the same ascent profile at the same location. We could not demonstrate a reduction in RVPG compared with placebo treatment despite reductions in AMS severity and better arterial oxygenation. Limited by small sample size, our data do not support recommending acetazolamide for the prevention of HAPE in mountaineers ascending rapidly to over 4,500 m.NEW & NOTEWORTHY This randomized, placebo-controlled, double-blind study is the first to investigate whether acetazolamide, which reduces acute mountain sickness (AMS), inhibits short-term hypoxic pulmonary vasoconstriction, and also prevents high-altitude pulmonary edema (HAPE) in a fast-climbing ascent to 4,559 m. We found no statistically significant reduction in HAPE incidence or differences in hypoxic pulmonary artery pressures compared with placebo despite reductions in AMS and greater ventilation-induced arterial oxygenation. Our data do not support recommending acetazolamide for HAPE prevention.
Keywords: AMS; Diamox; HAPE; acetazolamide; acute mountain sickness.