Acetazolamide (Diamox) for Altitude Sickness
Acetazolamide 125 mg twice daily is the recommended first-line prophylactic medication for altitude sickness prevention, started the night before ascent and continued for 2-3 days after reaching terminal altitude. 1
Prevention Dosing and Timing
Standard prophylactic dose:
- 125 mg twice daily (250 mg total daily) is the optimal dose, balancing efficacy with side effects 1, 2
- Start the night before ascent for maximum effectiveness 3
- Continue for 2-3 days after reaching terminal altitude, then discontinue 1
Alternative dosing considerations:
- 250 mg twice daily (500 mg total) may be considered for rapid ascents above 3,500 m where physical demands are high, though this increases side effects 4
- Do not use 62.5 mg twice daily—this dose is ineffective, with a number needed to harm of 9 compared to standard dosing 5
- Day-of-ascent dosing shows slightly higher AMS rates (48% vs 39%) and should be avoided when possible 3
Treatment of Established Altitude Sickness
For active acute mountain sickness:
- Acetazolamide 250 mg orally, repeated at 8 hours, effectively treats established AMS 6
- After 24 hours of treatment, 83% of patients recover versus 0% with placebo 6
- Improves arterial oxygenation by approximately 4 mmHg and reduces alveolar-arterial oxygen gradient 6
Mechanism and Additional Benefits
How acetazolamide works:
- Inhibits carbonic anhydrase, causing metabolic acidosis that stimulates ventilation and improves oxygenation 1
- Produces mild diuresis 1
- In hypertensive patients, provides additional blood pressure lowering benefit while improving oxygen saturation 7, 1
- May reduce subendocardial ischemia risk at high altitude 1
Special Populations
Cardiovascular patients:
- Continue all pre-existing cardiac medications at altitude 1
- Add acetazolamide using standard dosing (125 mg twice daily) 1
- Exercise caution when combining with other diuretics due to dehydration and electrolyte imbalance risk 1
Women:
- Have statistically higher AMS risk than men and require closer monitoring 1
- Consider iron supplementation (200 mg daily) as iron deficiency impairs acclimatization 1
- Standard acetazolamide dosing applies 1
Pediatric patients:
- No randomized trials exist for children; recommendations extrapolated from adult data 1
- Dose adjustment by weight using same principles 1
Common Side Effects
Expected adverse effects (generally mild and dose-related):
- Paresthesias (tingling in fingers, toes, lips) 1
- Altered taste (particularly carbonated beverages) 1
- Increased urination 1
- Vertigo 1
Critical Limitations
What acetazolamide does NOT prevent:
- Acetazolamide is NOT effective for preventing high-altitude pulmonary edema (HAPE), showing only 35% reduction versus 70-100% with nifedipine, tadalafil, or dexamethasone 8
- For HAPE-susceptible individuals, use nifedipine extended-release 20 mg every 8 hours instead, started with ascent and continued 3-4 days at terminal altitude 1
Non-Pharmacologic Prevention (Essential Foundation)
Gradual ascent remains the most effective prevention:
- Ascend 300-600 m per day above 2,500 m 1
- Include rest day every 600-1,200 m of elevation gain 1
- Avoid vigorous exertion before acclimatization 1
- Stop ascent immediately if symptoms develop 1
Common Pitfalls to Avoid
- Continuing ascent despite early symptoms markedly increases severe illness risk 1
- Using inadequate doses (62.5 mg twice daily is ineffective) 5
- Prolonging acetazolamide beyond 2-3 days at terminal altitude unnecessarily increases cumulative side effects 1
- Relying solely on medication without gradual ascent strategy 1
- Underestimating hydration needs, which worsens symptoms 1