What is the recommended prophylaxis for altitude sickness?

Prophylaxis of Altitude Sickness

Acetazolamide at a dose of 250-500 mg per day is the recommended first-line prophylactic medication for altitude sickness, starting one day before ascent above 3000m and continuing for 2-3 days after reaching the target altitude. 1, 2

Primary Prevention Strategies

Non-Pharmacological Approaches

• Slow, gradual ascent is the most effective prevention method, with recommended rates of 300-600 m/day above 2500m 3
• Include a rest day for every 600-1200m of elevation gained 3
• Avoid vigorous physical exertion before proper acclimatization 3, 4
• Delay further ascent if initial symptoms of altitude sickness appear 3, 4

Pharmacological Prophylaxis

Acetazolamide (First-Line)

• Dosing recommendations:
  • Standard dose: 250 mg twice daily or 500 mg once daily 2, 1
  • For rapid ascent to altitudes >3500m (military or emergency personnel): 500-750 mg/day may be more effective 2
  • Start medication one day before reaching 3000m altitude 5, 4
  • Continue for 2-3 days after arrival at the terminal altitude 3, 4
• Mechanism: Carbonic anhydrase inhibitor that causes mild diuresis and metabolic acidosis, which stimulates ventilation and improves oxygenation 3
• Efficacy: Associated with a 48% relative risk reduction compared to placebo 1
• Side effects: Paresthesias, altered taste for carbonated beverages, polyuria, and potential for transient myopic shift 3

Alternative Prophylactic Medications

• Nifedipine (calcium channel blocker):
  • Particularly effective for prevention of high-altitude pulmonary edema (HAPE) 3
  • Recommended for patients with history of HAPE 3, 4
  • Start with ascent and continue for 3-4 days after arrival at terminal altitude 3
• Dexamethasone:
  • Alternative when acetazolamide is contraindicated 3
  • Effective for prevention of severe forms of altitude sickness 4, 6
• PDE5 inhibitors (sildenafil, tadalafil):
  • May be considered for HAPE prophylaxis 3
  • Caution: tadalafil has been associated with severe acute mountain sickness in some subjects 3

Special Considerations

Cardiovascular Conditions

• Patients with cardiovascular disease should continue pre-existing medications at high altitude 3
• Acetazolamide may reduce the risk of subendocardial ischemia at high altitude in healthy subjects 3
• For patients with heart failure, acetazolamide should be carefully evaluated when used with other diuretics due to risk of dehydration and electrolyte imbalances 3
• Hypertensive patients may benefit from acetazolamide, which can lower blood pressure at high altitude while improving oxygen saturation 3

Pediatric Patients

• No randomized trials exist for prevention or treatment of HAPE in children 3
• Recommendations for children are based on adult trials 3
• Same principles apply: slow ascent, proper acclimatization, and similar medication dosing adjusted for weight 3

Treatment of Established Altitude Illness

• Immediate descent to lower altitude is the primary treatment for all forms of altitude illness 3, 4
• Supplemental oxygen administration is effective when available 3, 6
• Acetazolamide (500 mg/day) can be used to treat mild acute mountain sickness 4
• Dexamethasone is first-line treatment for severe acute mountain sickness/high altitude cerebral edema 4, 6
• Nifedipine is effective for treatment of high altitude pulmonary edema 4

Common Pitfalls and Caveats

• Underestimating the importance of gradual ascent and proper acclimatization 3, 4
• Continuing ascent despite early symptoms of altitude sickness 3, 6
• Inadequate hydration, which can worsen symptoms 3
• Starting prophylactic medication too late (should begin before ascent above 3000m) 5, 2
• Relying solely on medication without proper acclimatization protocols 6
• Failing to recognize early symptoms of more severe forms of altitude illness 4, 6