Twenty-three volunteers participated in a double-blind, randomized trial comparing the steroid dexamethasone 4 mg to placebo every 12 h as prophylaxis against acute mountain sickness (AMS) during a rapid ascent to a shelter on Mt Chaclataya, Bolivia. From sea level, subjects were transported by air and land vehicles to 5334 m within a 72-h period. They were evaluated by cerebral scores derived from the Environmental Symptom Questionnaire and confirmed by AMS-C and AMS-R scores. After 6–8 h at high altitude (day 3), the number of ill persons in the dexamethasone group was less than those ill in the placebo group (χ2 = 7.43, p = 0.01) by chi-square and Fisher's exact tests. After 20 h at high altitude (day 4), the contrast between groups diminished (χ2 = 2.10, p = 0.214). ANOVA and t-test showed that mean cumulative AMS scores of the dexamethasone group were significantly lower ( p = 0.01, p = 0.02) than those of the placebo group for both days at high altitude, despite an approximate 82% increase in the mean cumulative score of the dexamethasone group from day 3 to day 4. We conclude that dexamethasone 4 mg every 12 h, though initially effective, was not sufficient to sustain prophylaxis from AMS symptoms at 5334 m.

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