What is the best medication to prevent Acute Mountain Sickness (AMS)?

Best Medication for Preventing Acute Mountain Sickness

Acetazolamide is the best medication for preventing Acute Mountain Sickness (AMS), with a recommended dosage of 125mg twice daily starting 24 hours before ascent. 1

Pharmacological Prevention Options

First-Line Medication: Acetazolamide

• Mechanism: Carbonic anhydrase inhibitor that increases ventilation and reduces AMS symptoms
• Dosing regimen: 125mg twice daily starting 24 hours before ascent 1
• Higher doses (500-750mg/day) may be more effective for rapid ascents above 3,500m 1
• Effectiveness: Significantly reduces AMS incidence and severity 1, 2
• May also reduce the risk of subendocardial ischemia at high altitude 1

Second-Line Medication: Dexamethasone

• Can be used when acetazolamide is contraindicated
• Dosing: 4mg four times daily 3
• Important limitation: Should never be used for more than 2-3 days due to side effect profile 3
• Particularly useful for treating cerebral symptoms when they occur 1

For HAPE-Susceptible Individuals

• Nifedipine: 20mg three times daily 1, 4
  • Mechanism: Decreases pulmonary artery pressure
  • Should be started one day before climbing and continued during ascent for those with history of HAPE 4
• Alternative options: PDE5 inhibitors (sildenafil, tadalafil) 1

Non-Pharmacological Prevention Strategies

The most effective prevention strategy is slow ascent:

• Limit ascent to <400m/day above 2,500m 1
• Include a rest day for every 600-1200m gained 1
• Pre-acclimatization for 2 weeks with >8h/day at progressively increasing altitudes (if facilities available) 1
• Maintain proper fluid intake 1

Special Considerations

Timing of Acetazolamide Administration

• Traditional approach: Start 24 hours before ascent
• Day-of-ascent dosing may be slightly less effective but still beneficial and could improve compliance 5
• Research shows only 9% greater incidence of AMS with day-of-ascent dosing compared to night-before dosing 5

Patient-Specific Factors

• Women may have higher AMS risk; consider timing altitude exposure during luteal phase of menstrual cycle 1
• Patients with cardiovascular conditions should consult physicians for medication adjustments 1
• Caution when combining acetazolamide with other diuretics due to increased dehydration risk 1

Clinical Pearls and Pitfalls

• Acetazolamide is not a substitute for proper acclimatization but rather an adjunct
• Never rely solely on medication; always incorporate gradual ascent when possible
• Recognize early symptoms of AMS (headache, insomnia, anorexia, nausea, dizziness) to prevent progression to life-threatening conditions like HAPE and HACE
• Descent remains the definitive treatment for severe AMS, HAPE, or HACE
• Military experience confirms acetazolamide's effectiveness in high-altitude expeditions (19,000-23,000 ft) 2

When to Consider Alternative Approaches

• For patients with sulfa allergies: Dexamethasone may be used as an alternative
• For HAPE-susceptible individuals: Consider nifedipine as primary prophylaxis 1, 4
• For short-duration, high-altitude exposure: Day-of-ascent acetazolamide dosing may be reasonable 5