The purpose of this randomized, placebo-controlled double-blind trial is to evaluate efficacy of acetazolamide in preventing overt altitude-related adverse health effects (ARAHE) in lowlanders with chronic obstructive pulmonary disease (COPD) developing early signs of altitude-illness during altitude travel.

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).

Inclusion criteria

• Men and women, age 35-75 y, living at low altitude (<800 m).

• COPD diagnosed according to the Global Initiative for Obstructive Lung Disease (GOLD) guidelines, forced expiratory volume in one second 40-80% predicted, pulse oximetry ≥92%, PaCO2 <6 kilopascal, breathing ambient air at 760 m.

• One of the following early signs and/or symptoms of impending altitude-illness identified by self-monitoring during ascent to or stay at 3100 m:

  • Pulse oximetry SpO2≤84%
  • Headache or nausea/vomiting or fatigue/weakness or dizziness/light-headedness of at least moderate intensity

Exclusion criteria

• COPD exacerbation, very severe COPD with hypoxemia or hypercapnia at 760 m (see above).
• Other lung disease, relevant comorbidities (such as uncontrolled cardiovascular disease, i.e., unstable arterial hypertension, coronary artery disease; previous stroke; obesity (body mass index >35 kg/m2); internal, neurologic, rheumatologic or psychiatric disease; current heavy smoking (>20 cigarettes per day).
• Renal failure and/or allergy to sulfonamides.
• Patients who do not have early signs and/or signs of impending altitude-illness by self-monitoring (as defined above) at 3'100m will not be included.

An independent pharmacist will prepare identically looking active and placebo capsules labelled with secret codes. Codes will be concealed to investigators and patients until completion of data analysis.