### What you need to know A 25 year old man plans to trek to Everest Base Camp (5545 m) in Nepal for charity. He asks you for a prescription of acetazolamide to prevent mountain sickness. For most people, mountain sickness is a self limiting illness, but it can become life threatening. It is estimated that more than 100 million people per year travel to the hypoxic environments found at altitudes above 2500 m,1 and at least 10% to 20% of unacclimatised individuals develop acute mountain sickness at this height.2 Acclimatisation to altitude involves multiple physiological changes, occurring over days to weeks, which enable individuals to function better in these hypoxic environments. If this natural adaptation is surpassed by the rate of exposure to altitude, acute mountain sickness can occur. Acetazolamide can help to prevent acute mountain sickness developing and has fewer side effects than alternative drugs such as dexamethasone, which can mask symptoms and therefore carries greater risks.2345 Acetazolamide causes mild diuresis and increases renal excretion of bicarbonate, causing a mild metabolic acidosis which in turn increases respiratory rate (improving oxygenation). In the UK, prescribing acetazolamide for travel is an optional service, not included in the general practitioner’s contract. Some GPs may decide not to prescribe acetazolamide on this basis, or because they feel it is outside the scope of their practice. This article is an approach to discussing travel and activity at high altitude, prevention of sickness, and acetazolamide prescription for non-specialists. ### History #### What does the person know about acute mountain sickness? Symptoms of acute mountain sickness …