What is the dose for acetazolamide (carbonic anhydrase inhibitor) for altitude sickness?

Acetazolamide Dosing for Altitude Sickness

For altitude sickness prevention, acetazolamide should be administered at a dose of 125-250 mg twice daily starting 24 hours before ascent and continuing during the stay at high altitude. 1

Dosing Recommendations

• Prophylaxis (Prevention):

  • 125-250 mg twice daily starting 24 hours before ascent 1, 2
  • Continue throughout the stay at altitude
  • Higher doses (500-750 mg/day) may be more effective for rapid ascents above 3,500m, particularly for military or emergency personnel 3

• Treatment (for established mild AMS):

  • 250 mg twice daily 1

Mechanism and Efficacy

Acetazolamide is a carbonic anhydrase inhibitor that:

• Increases ventilation and improves oxygenation
• Reduces the risk of AMS symptoms
• Lowers blood pressure at high altitude while improving oxygen saturation
• May reduce central sleep apnea that occurs at altitude 1

Even when started on the day of ascent, acetazolamide can decrease the severity of AMS symptoms, though efficacy may be slightly lower than when started earlier 1. Studies show acetazolamide significantly reduces AMS incidence (14% vs. 45% with placebo) in high-risk settings 4.

Indications and Patient Selection

Acetazolamide prophylaxis is particularly beneficial for:

• Individuals with a history of previous AMS
• Those with no recent acclimatization to high altitude
• Travelers with cardiovascular conditions planning high altitude travel
• Situations involving rapid ascent to altitudes above 3,350m (11,000 feet), where AMS risk ranges from 35-50% 1, 2

Contraindications

Acetazolamide is contraindicated in patients with:

• Kidney stones
• Aplastic anemia
• Sickle cell disease
• Sulfa allergy (important!)
• Severe hepatic disease
• Severe renal disease
• Adrenocortical insufficiency
• Hyperchloremic acidosis 1

Side Effects and Monitoring

Common side effects:

• Paresthesias (tingling in extremities)
• Vertigo
• Altered taste
• Increased urination
• Allergic dermatitis/conjunctivitis 1

Serious side effects:

• Kidney stones
• Metabolic acidosis
• Blood dyscrasias
• Stevens-Johnson syndrome
• Serum electrolyte imbalances
• Lethargy
• Suppression of appetite 1

Important Clinical Pearls

1. Caffeine interaction: Limit caffeine intake when taking acetazolamide as it may worsen side effects and impact treatment efficacy 1

2. Monitoring: Check serum electrolytes, renal function, and acid-base status when using acetazolamide, especially in longer courses 1

3. Medication combinations: Avoid combining acetazolamide with other diuretics due to increased risk of dehydration and electrolyte imbalances 1

4. Non-pharmacological prevention: Always emphasize gradual ascent (300-600m/day above 2500m), rest days, adequate hydration, and avoiding overexertion during the first days at altitude 1, 5

5. Severe cases: Immediate descent is the primary treatment for severe altitude illness; supplemental oxygen should be used to maintain saturation >90% if available 1

6. Special populations: Women may have a higher risk of acute mountain sickness and may benefit from iron supplementation before altitude exposure 1