prophylactic (preventative) measures against development of mountain sickness

Last edited 04/2022 and last reviewed 07/2022

It is advised that climbers should acclimatise if climbing to high altitude.

• if above 3000m (10,000 feet), no more than 300m (1000 feet) should be climbed per 24 hour period (1)
  • if a climber develops symptoms of mild altitude sickness then he/she should rest for 24 hours at that altitude
  • if a climber has more severe symptoms then he/she must descend to the last altitude at which they felt well. This should occur whether or not they use drugs
  • if rapid ascent is unavoidable then acetozolamide is beneficial
  • a rest day every 3 days or 1000 m

Prevention of acute mountain sickness (AMS) (2)

• acetazolamide can be used for preventing AMS according to the National Travel and Health Network Centre and Fit For Travel recommendations (not licensed for this this indication)
• acetazolamide prevents AMS by mimicking the body naturally adjusting to a change in environment
• a Cochrane review demonstrated acetazolamide reduced the risk of AMS vs placebo by a factor of 0.47 (n=2,301, 16 studies). Acetazolamide was administered one to five days prior to ascent with doses of up to 500mg/day to adults at risk of AMS
  
  
  • prescribing and dosing
    • use acetazolamide 125mg twice daily (off-label).
    • smaller doses of acetazolamide can be given by halving 250mg tablets which are scored.
    • prescribe acetazolamide one to two days before gradual ascent to high altitude and continue acetazolamide for at least two days after reaching the highest point.
    • advise people to take the second dose of acetazolamide at dinnertime rather than at bedtime as it is a diuretic.
    • trial acetazolamide for two days before ascent to high altitude because side effects can resemble the symptoms of AMS
    • check local guidelines for processes on prescribing acetazolamide for travel
• cautions
  • take into account the contraindications and cautions of acetazolamide and check if it is appropriate for the person
  • avoid acetazolamide in people with a history of anaphylaxis or severe allergy to suphonamide as it is a sulphonamide derivative
    
    
• the NHS review did not recommend any other medications for use in AMS prophylaxis
  • overall, evidence for the use of the medicines listed below to prevent AMS is inconclusive and for some, side effects are a concern:
    • aspirin
    • dexamethasone
      • Using dexamethasone has been suggested by some organisations to help prevent AMS. However, the Cochrane review (n=176) assessing four parallel studies comparing dexamethasone with placebo found dexamethasone does not prevent AMS at any dose and does not aid acclimatisation.
    • ibuprofen
    • iron supplements
    • magnesium citrate
    • spironolactone
    • sumatriptan

Notes:

• if acetazolamide is used, treatment should be started at least one day before ascent and continued until adequate acclimatisation is judged to have occurred
  • side effects, which include paraesthesia and mild diuresis, are common but usually well tolerated
  • acetazolamide is a sulphonamide, and allergic reactions can occur
  • acetazolamide is not a substitute for acclimatisation
    
    
• phosphodiesterase Inhibitors as prophylaxis for altitude sicknes: tadalafil and sildenafil (3)
  • because of its pulmonary vasodilatory effects, the phosphodiesterase inhibitor tadalafil can be used for prevention of high altitude pulmonary edema (HAPE)
    • it has been demonstrated that tadalafil prevents the disease in known HAPE-susceptible individuals. No studies have examined whether the drug can also be used to treat HAPE
    • although no systematic studies have examined whether sildenafil is effective in the prevention and treatment of HAPE, it is worth considering this medication as well because it has a similar mechanism of action and should exert a similar benefit as tadalafil and because there are reports of its use in clinical practice as treatment for HAPE or prevention in children with underlying cardiopulmonary disease and HAPE

Reference:

• 1) Pulse (2002), 62(31),36.
• 2) NHS Specialist Pharmacy Service (April 2022). Using medicines for preventing acute mountain sickness
• 3) Luks AM, Swenson ER.Medication and dosage considerations in the prophylaxis and treatment of high-altitude illness. Chest. 2008 Mar;133(3):744-55.