Altitude Sickness Prevention in Healthy Adults
The most effective prevention strategy is gradual ascent at 300-600 m/day above 2500 m, combined with acetazolamide 250 mg twice daily (or 500 mg once daily) starting 1-2 days before ascent for those at higher risk or unable to ascend slowly. 1
Primary Prevention: Gradual Ascent
The cornerstone of altitude sickness prevention is controlled, gradual ascent rather than pharmacological intervention alone:
- Ascend at a rate of 300-600 m/day above 2500 m to allow physiological acclimatization 1, 2
- Include a rest day for every 600-1200 m of elevation gained to consolidate acclimatization 1
- Avoid vigorous physical exertion in the first 24-48 hours after reaching a new altitude, as exercise before acclimatization increases risk 1, 3
- Stop ascending and rest if initial symptoms appear (headache, nausea, dizziness, insomnia) rather than continuing upward 1
More than 50% of unacclimatized individuals develop acute mountain sickness above 4500 m with rapid ascent (>300 m/day), emphasizing that speed of ascent is the primary modifiable risk factor 1.
Pharmacological Prophylaxis: Acetazolamide
Acetazolamide is the first-line prophylactic medication for those unable to ascend gradually or with a history of altitude sickness 1:
- Standard dosing: 250 mg twice daily or 500 mg once daily 1, 2
- Start 1-2 days before ascent and continue for 2-3 days after reaching terminal altitude 1
- Mechanism: carbonic anhydrase inhibitor that causes mild metabolic acidosis, stimulating ventilation and improving oxygenation 1
- Common side effects include paresthesias (tingling), altered taste, and increased urination, which are generally mild but dose-related 1
Acetazolamide reduces the risk of acute mountain sickness but does not eliminate it entirely; some travelers will still develop symptoms despite prophylaxis 4.
Supportive Measures
Beyond ascent rate and medication, several practical measures reduce altitude sickness risk:
- Maintain adequate hydration throughout ascent, as dehydration worsens symptoms and hypoxic diuresis increases fluid losses 5, 1
- Avoid alcohol and smoking, which impair acclimatization 3
- Consider a high-carbohydrate, low-fat, low-salt diet to aid prevention 3
Alternative Medications for Specific Scenarios
Nifedipine is specifically indicated for high-altitude pulmonary edema (HAPE) prevention in those with a prior history:
- Dosing: start with ascent and continue 3-4 days after arrival at terminal altitude 1
- Recurrence rate of HAPE is 62% with rapid ascent in susceptible individuals, making prophylaxis essential for this subgroup 1
Dexamethasone is an alternative when acetazolamide is contraindicated (e.g., sulfa allergy), though it is not routinely recommended as first-line prophylaxis 1, 3.
Common Pitfalls to Avoid
- Underestimating the importance of gradual ascent: Many travelers rely solely on medication while ascending too rapidly, which significantly increases risk 1
- Inadequate hydration: The combination of increased respiratory water loss and hypoxic diuresis makes dehydration common and worsens symptoms 5, 1
- Continuing ascent despite symptoms: Early symptoms of acute mountain sickness should prompt a rest day, not continued climbing 1
- Prolonged acetazolamide use beyond 2-3 days at terminal altitude: This is unnecessary for standard prevention and increases cumulative side effects 1
When to Seek Immediate Medical Attention
Descent is mandatory if severe symptoms develop:
- Severe headache unrelieved by acetaminophen suggests high-altitude cerebral edema 2
- Ataxia, confusion, or altered mental status indicates progression to life-threatening cerebral edema 2
- Dyspnea at rest, chest tightness, or cough with pink frothy sputum suggests high-altitude pulmonary edema 2
Immediate descent of at least 300 m and supplemental oxygen (if available) are the primary treatments for severe altitude illness, as these conditions can be fatal without prompt intervention 2, 6.