Prophylactic Low-Dose Acetazolamide Reduces the Incidence and Severity of Acute Mountain Sickness

Tissot van Patot, Martha C., Guy Leadbetter III, Linda E. Keyes, Kirsten M. Maakestad, Sheryl Olsen, and Peter Hackett. High Alt. Med. & Biol. 9:289–293, 2008.—Previous studies have shown low-dose acetazolamide to be effective in preventing AMS in persons already at high altitude and then moving higher, a relatively low risk situation. We wished to evaluate prophylactic administration of low-dose acetazolamide for reducing the incidence and severity of AMS in a high-risk setting: rapid ascent from 1600 to 4300 m. We performed a double-blind, randomized, placebo-controlled study with human subjects (n = 44) exposed to 4300 m for 24 h. Subjects were treated for 3 days prior to ascent to 4300 m and during day 1 at altitude with placebo (n = 22) or acetazolamide 250 mg/day (125 mg bid, n = 22). AMS diagnosis required both an AMS-C score from the Environmental Symptom Questionnaire-III ≥0.7 and a Lake Louise Symptom (LLS) questionnaire score ≥3 plus headache. Acetazolamide reduced the incidence of AMS compared to placebo-treated subjects (14% vs. 45%, respectively, p = 0.02), and the number needed to treat was 3. The AMS-C and LLS scores were lower in acetazolamide-treated subjects, indicating less severe AMS. Low-dose acetazolamide administered prior to ascent and on day 1 at 4300 m effectively reduced the incidence and severity of AMS in a high-risk setting.