Sickness Evaluation at Altitude With Acetazolamide at Relative Doses
Condition: Acute Mountain Sickness
MeSH terms: Altitude Sickness
Study type: Interventional
Phase: Phase 1

Summary: 
      The specific aim of this study is to evaluate whether acetazolamide 125mg daily is no worse
      than acetazolamide 250mg daily in decreasing the incidence of acute mountain sickness (AMS)
      in travelers to high altitude. The study population is hikers who are ascending at their own
      rate under their own power in a true hiking environment at the White Mountain Research
      Station, Owen Valley Lab (OVL) and Bancroft Station (BAR), Bancroft Peak, White Mountain,
      California
    

Detailed description: 
      Acute mountain sickness (AMS) is a constellation of symptoms including headache, sleep
      disturbance, fatigue, dizziness, and nausea, vomiting, or anorexia that commonly occurs in
      travelers ascending to altitudes above 2,500m. AMS incidence varies based on altitude and
      ascent profile with rates reported from 25 to 75% in tourists, trekkers, and mountaineers at
      North American altitudes. Symptom onset is typically six to twelve hours after arrival at
      high altitude. This self-limited disease can be debilitating when severe, and left
      unrecognized or untreated may progress to potentially fatal high altitude cerebral edema
      (HACE). While gradual ascent has proven effective in preventing AMS, this approach is often
      impractical to recreationists, search and rescue, disaster relief, and military operations.

      Acetazolamide increases minute ventilation by 10-20% in subjects at altitude, and hastens
      acclimatization. It is well established that acetazolamide's main site of action is in the
      kidney, where it generates a metabolic acidosis through renal bicarbonate wasting and
      attenuates the effects of hypoxemic-induced respiratory alkalosis. Recommended dosing of
      acetazolamide for AMS prophylaxis has significantly decreased since early days of use in the
      1960s. The current recommended dose of acetazolamide for this indication is 125 mg twice
      daily, as opposed to historical recommendations of 500mg or 750mg daily. Multiple
      meta-analyses have concluded that when compared with higher doses, 250mg of acetazolamide
      daily has been shown to be equally efficacious, with the added benefit of decreasing side
      effects including paresthesias and dysgeusia. A randomized controlled trial confirmed
      effectiveness of acetazolamide 125mg twice daily in prevention of AMS when started prior to
      ascent. In this study, it was found that 125mg twice daily corresponded to a range of
      3-5mg/kg/day, depending on subject weight. Within this range, those on the lower dosing range
      did not have a greater incidence or severity of AMS. For subjects weighing between 50kg (110
      lbs) - 83kg (183 lbs), a dose of 250mg/day acetazolamide would fall in this range.
      Interestingly, mountaineers and trekkers have anecdotally reported protection against AMS
      with 125mg/day of acetazolamide, a dose below 3-5mg/kg for anyone over 41kg (91lb).

      Finding the lowest effective dose of acetazolamide for AMS prophylaxis is important because
      side effects of this medication can mimic AMS, decreasing the specificity of disease scoring
      on the validated Lake Louise Questionnaire (LLQ) and subsequent AMS diagnosis and
      chemoprophylactic effectiveness.Keeping in mind that LLQ is scored based on symptoms of
      headache, gastrointestinal symptoms, fatigue and weakness, and dizziness and lightheadedness,
      whatever effect acetazolamide has on AMS prevention may be obscured by its side effects that
      mimic the very same disease. Falsely positive LLQ scores in trekkers and mountaineers taking
      acetazolamide prophylaxis may lead to unnecessary pharmacologic treatment or even evacuation.
      From the perspective of high altitude research, participants randomized to or already taking
      acetazolamide may skew study results by decreasing LLQ specificity and potentially leading
      researchers to overestimate incidence of AMS.
    

Intervention name(s): Acetazolamide Pill
Intervention type(s): Drug
Intervention description(s): Acetazolamide pill
Other intervention name(s): Diamox
Intervention MeSH terms: Acetazolamide
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Double blind randomized controlled trial
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Prevention
Keywords: acetazolamide; chemoprophylaxis; altitude