From the Guidelines
The most effective prophylaxis for Acute Mountain Sickness (AMS) is acetazolamide, which should be taken at a dose of 125-250 mg twice daily, starting 24 hours before ascent and continuing for 48 hours after reaching the target altitude, as supported by recent guidelines 1. When considering altitude prophylaxis, several factors come into play, including the individual's health status, the altitude of destination, and the rate of ascent.
- Gradual ascent is a crucial non-pharmacological strategy, with recommendations to climb no more than 300-500 meters per day above 2500 meters and include a rest day every 1000 meters 1.
- Proper hydration, avoiding alcohol, and moderate physical activity during the first 24-48 hours at altitude are also important considerations for reducing AMS risk.
- Acetazolamide works by causing mild metabolic acidosis through carbonic anhydrase inhibition, which stimulates ventilation and improves oxygenation, effectively speeding up acclimatization 1.
- For individuals with sulfa allergies or who cannot tolerate acetazolamide, dexamethasone can be used as an alternative at 4 mg every 6-12 hours, although this is less commonly recommended due to potential side effects.
- It's also important to note that women may have a higher risk of AMS, and thus, systematic screening using the Lake Louise Scoring system and consideration of chemosensitivity tests prior to ascent may be beneficial for this group 1.
- Additionally, pre-acclimatization strategies, such as intermittent hypoxia exposures, can be effective for eliciting ventilatory acclimatization and may be particularly beneficial when combined with respiratory muscle training for women 1.
From the Research
Altitude Prophylaxis for Acute Mountain Sickness (AMS)
Recommended Prophylaxis
- Acetazolamide is the drug of first choice for AMS prophylaxis, as it increases ventilation and has been shown to decrease the incidence and severity of AMS 2, 3, 4.
- The recommended dosage of acetazolamide varies, but common dosages include 250-500 mg 12-24 hours before ascent 2 and 500-750 mg/day within 24 hours of altitude exposure 3.
Alternative Prophylaxis
- Nifedipine, a potent vasodilator, is recommended for individuals with a history of high-altitude pulmonary edema (HAPE), but it has not been shown to prevent AMS in individuals not susceptible to HAPE 2, 5.
Important Considerations
- Acclimatization is still necessary, even with pharmacological prophylaxis, and can be achieved by a slow ascent at a climbing rate of 300 to 600 m in one day or by spending at least nine or more nights at an altitude higher than 2500 m a.s.l. in the last 30 days before ascent 2.
- Acetazolamide may not be effective in preventing high-altitude pulmonary edema (HAPE), and other medications such as nifedipine, dexamethasone, and tadalafil may be more effective for HAPE prevention 6.