This randomized placebo-controlled, double-blind, parallel-design trial will evaluate effectiveness of acetazolamide in reducing the incidence of predefined altitude-related adverse health effects in lowlanders with chronic obstructive pulmonary disease (COPD) travelling to high altitude and developping early symptoms and/or signs of impending altitude-illness. Qualifying participants will be randomized 1:1 to acetazolamide or placebo treatment during their further stay of 2 days at 3'100 m.
An interim-analysis will be performed after the first year of the study or when 38 participants are randomized, whichever comes first. Symmetric stopping boundaries at P\<0.001 will be applied (Peto approach).
