What medication is recommended for preventing altitude sickness at high altitudes?

Recommended Medication for High Altitude Sickness Prevention

Acetazolamide is the first-line medication for preventing altitude sickness, with a standard dose of 125 mg twice daily (250 mg total daily) or 250 mg twice daily (500 mg total daily) starting 24 hours before ascent. 1

Primary Medication: Acetazolamide

Acetazolamide works as a carbonic anhydrase inhibitor that causes mild diuresis and metabolic acidosis, which stimulates ventilation and improves oxygenation at high altitude. 1 This mechanism directly addresses the underlying pathophysiology of altitude sickness by enhancing acclimatization. 2

Dosing Recommendations

• Standard prophylactic dose: 125 mg twice daily (total 250 mg/day) is highly effective at diminishing the risk of altitude illness 2
• Alternative dosing: 250 mg twice daily (total 500 mg/day) or 500 mg once daily for standard prevention 1
• For rapid ascent to >3,500 m with physically demanding activity: 500-750 mg/day appears most effective 3
• Timing: Begin 24 hours before ascent 4, 3

Additional Benefits Beyond AMS Prevention

Acetazolamide provides multiple protective effects at high altitude:

• Lowers blood pressure while improving oxygen saturation 5
• Reduces central sleep apnea that commonly occurs at altitude 5
• May reduce risk of subendocardial ischemia in healthy subjects 1

Alternative Medications for Specific Conditions

For High-Altitude Pulmonary Edema (HAPE) Prevention

Nifedipine is the drug of choice for individuals with a history of HAPE, with dosing of 20 mg three times daily (extended-release formulation preferred), starting one day before ascent and continuing for 3-4 days after reaching terminal altitude. 1, 4 Nifedipine works as a potent vasodilator that decreases pulmonary artery pressure. 4

PDE5 inhibitors (sildenafil, tadalafil) are alternatives to nifedipine for HAPE prevention, though tadalafil has been associated with severe acute mountain sickness in some subjects. 1

When Acetazolamide is Contraindicated

Dexamethasone is the alternative when acetazolamide cannot be used (such as in sulfa allergy). 1 However, acetazolamide remains superior for prophylaxis because it aids acclimatization rather than just masking symptoms.

Special Population Considerations

Hypertensive Patients

Hypertensive patients may particularly benefit from acetazolamide as it lowers blood pressure at high altitude while improving oxygen saturation and mountain sickness symptoms. 5 The combination of nifedipine/telmisartan effectively lowers blood pressure in hypertensive patients at altitude around 3,300 m. 5

Cardiovascular Disease Patients

Patients with pre-existing cardiovascular conditions should continue their baseline medications at high altitude and may add acetazolamide for altitude sickness prevention. 1 For heart failure patients using acetazolamide, careful evaluation is needed when combined with other diuretics due to dehydration and electrolyte imbalance risks. 1

Pediatric Patients

Children should receive the same medications as adults with weight-adjusted dosing, as recommendations are extrapolated from adult trials. 1 The same principles of slow ascent and proper acclimatization apply. 1

Critical Context: Non-Pharmacologic Prevention Remains Essential

Gradual ascent is the most effective prevention method, with recommended rates of 300-600 m/day above 2,500 m, including a rest day for every 600-1,200 m of elevation gained. 1 Medication should complement, not replace, proper acclimatization strategies.

The risk of altitude illness with rapid ascent to >3,350 m ranges from 35% to nearly 50% 2, making this a high-priority travel medicine concern comparable to traveler's diarrhea risk in high-risk destinations. 2

Common Pitfalls to Avoid

• Starting medication too late: Begin acetazolamide 24 hours before ascent, not upon arrival 3
• Inadequate hydration: Dehydration worsens symptoms and should be actively prevented 5
• Continuing ascent with symptoms: Delay further ascent if initial altitude sickness symptoms appear 1
• Underdosing for rapid, demanding ascents: Use higher doses (500-750 mg/day) for military or emergency personnel requiring rapid ascent with immediate physical demands 3