What are the prophylactic measures for acute mountain sickness (AMS)?

From the Guidelines

Altitude sickness prophylaxis should begin with acetazolamide (Diamox) as the primary medication, taken at a dose of 125mg twice daily, starting 24 hours before ascent and continuing for 48 hours after reaching the target altitude, as recommended by recent studies 1. When it comes to preventing altitude sickness, several key strategies can be employed to minimize the risk of acute mountain sickness (AMS) and other related conditions.

• Gradual ascent is crucial, with a recommended climb of no more than 1,000-1,500 feet per day when above 8,000 feet, and a rest day for every 3,000 feet gained 1.
• Staying well-hydrated and avoiding alcohol are also important measures to help the body acclimatize to lower oxygen levels at high altitudes.
• Considering spending a night at an intermediate altitude before reaching higher elevations can also be beneficial.
• Acetazolamide acts as a respiratory stimulant and promotes bicarbonate excretion, which helps counter the respiratory alkalosis that occurs at altitude 1.
• If symptoms develop despite prophylaxis, such as headache, nausea, fatigue, or dizziness, it is essential not to ascend further until symptoms resolve, and to descend if symptoms worsen, as severe altitude sickness can be life-threatening.
• For individuals who cannot tolerate acetazolamide, dexamethasone is an alternative at 4mg every 6 hours, though it's less ideal due to potential side effects with prolonged use.
• Systematic screening of AMS based on the Lake Louise Scoring system is recommended, especially for women who appear to have a statistically higher AMS risk 1.

From the Research

Altitude Sickness Prophylaxis

• Altitude sickness, also known as acute mountain sickness (AMS), can be prevented with the use of acetazolamide, a carbonic anhydrase inhibitor 2, 3, 4, 5, 6
• The efficacy of acetazolamide in preventing AMS has been demonstrated in several studies, with a relative-risk reduction of 48% compared to placebo 5
• The optimal dose of acetazolamide for prophylaxis is still debated, but doses of 250-750 mg/day have been shown to be effective in decreasing the incidence and severity of AMS 4, 5
• Acetazolamide has also been shown to reduce the symptoms of AMS, including headache, nausea, and fatigue, and to improve arterial oxygen concentrations 2, 6
• However, the evidence for the use of acetazolamide in preventing high-altitude pulmonary edema (HAPE) is limited, and other medications such as dexamethasone, tadalafil, and nifedipine may be more effective in this regard 3

Acetazolamide Dosing

• The dosing of acetazolamide for altitude sickness prophylaxis can vary, but common regimens include 125-250 mg twice daily, starting 24-48 hours before ascent 2, 4, 5
• Higher doses of acetazolamide (500-750 mg/day) may be more effective in preventing AMS, but may also increase the risk of adverse effects 4
• The timing of acetazolamide dosing is also important, with some studies suggesting that day of ascent dosing may be as effective as traditional dosing the night before ascent 2

Adverse Effects

• Acetazolamide can cause adverse effects, including nausea, vomiting, diarrhea, and fatigue, but these are generally mild and self-limiting 5, 6
• Higher doses of acetazolamide may increase the risk of adverse effects, and individual tolerance to the medication should be considered when determining the optimal dose 4, 5