Altitude Sickness Prevention Medication
Acetazolamide 250 mg twice daily (or 500 mg once daily) starting 1-3 days before ascent is the first-line medication for preventing altitude sickness, and should be continued for 3-4 days after reaching your final altitude. 1, 2
Primary Prevention Strategy
Before discussing medications, understand that gradual ascent remains the most effective prevention method and should be combined with pharmacological prophylaxis when appropriate 1:
- Ascend at 300-600 m/day above 2500m 1
- Include a rest day for every 600-1200m of elevation gained 1
- Avoid vigorous exertion before acclimatization 1
First-Line Medication: Acetazolamide
Recommended Dosing
Standard dose: 250 mg twice daily or 500 mg once daily 1, 2
- Start 1-3 days prior to ascent 2
- Continue for 3-4 days after reaching terminal altitude 2
- Lower doses of 125 mg twice daily have similar efficacy with potentially fewer side effects for gradual ascents 2, though 62.5 mg twice daily is NOT recommended as it failed to demonstrate equal effectiveness 3
Special Circumstances for Higher Dosing
For rapid ascents above 3500m (military, emergency personnel, or physically demanding activities): use 500-750 mg/day within 24 hours of altitude exposure 4. This higher dosing is specifically indicated when gradual ascent is not possible and immediate physical performance is required 4.
How Acetazolamide Works
The medication induces metabolic acidosis that stimulates respiratory drive, leading to 2:
- Increased ventilation even during sleep 2
- Improved arterial oxygen saturation (88-91% at altitude) 2
- Reduced periodic breathing and central sleep apnea 2
- Blood pressure reduction by 7-10 mmHg systolic 2
Common Side Effects
Expect mild, dose-related effects including 2:
- Paresthesias (tingling in fingers/toes)
- Altered taste (carbonated beverages taste flat)
- Increased urination
- Vertigo
Critical caveat: Maintain adequate hydration as dehydration worsens altitude symptoms 2.
Alternative Medications
Nifedipine for High-Altitude Pulmonary Edema (HAPE) Prevention
For patients with previous HAPE history: nifedipine should be started with ascent and continued for 3-4 days after arrival 1. This population has a 62% recurrence rate with rapid ascent and requires prophylaxis 1.
Dexamethasone
Use as an alternative when acetazolamide is contraindicated (sulfa allergy) 1.
Special Populations
Hypertensive Patients
Acetazolamide is particularly beneficial as it lowers blood pressure at altitude while improving oxygen saturation and reducing mountain sickness symptoms 2, 5. Continue pre-existing antihypertensive medications 1.
Women
Although no clear evidence shows greater vulnerability to acute mountain sickness in women, sex-dependent physiological reactions may contribute to increased vulnerability in some women 1. The same acetazolamide dosing applies, with no sex-specific adjustments needed 2.
Patients with Heart Failure
Exercise caution when combining acetazolamide with other diuretics due to risk of dehydration and electrolyte imbalances 1.
Pediatric Patients
Recommendations are based on adult trials with similar medication dosing adjusted for weight 1.
Common Pitfalls to Avoid
- Do not use 62.5 mg twice daily dosing - this failed noninferiority testing with a number needed to harm of 9 3
- Starting acetazolamide the morning of ascent rather than the night before increases AMS incidence by 9% 6, though severe AMS rates were similar 6
- Underestimating the importance of gradual ascent even when taking medication 1
- Inadequate hydration, which compounds altitude symptoms 1, 2