NCT03424226.

Trial name or title	Sickness evaluation at altitude with acetazolamide at relative dosages (SEAWARD)
Methods	To determine whether acetazolamide started the day of ascent is inferior to the standard night‐before‐ascent dose of acetazolamide for the prevention of acute mountain sickness (AMS) in travellers to high altitude. Acetazolamide has been examined in over 200 high altitude studies over the past 50 years, and is the most commonly used drug for AMS prevention in the high mountains of Nepal, Western Europe, and Africa. Current Wilderness Medical Society Practice Guidelines recommend a 125 mg dose of acetazolamide daily started the day or evening prior to ascent. However, day of ascent dosage has recently been found to be effective prophylaxis for severe AMS compared to placebo, but efficacy of day‐of‐ascent dosage has not been confirmed versus standard acetazolamide dosage.
Participants	Inclusion criteria Age 18‐ to 75‐year‐old healthy non‐pregnant volunteer Lives at low elevation (< 4000 ft) Arrange own transportation to White Mountain Research Station, Bishop, CA by Friday evening of study weekend Available for full study duration (Friday p.m. to Sunday a.m.) Exclusion criteria Age < 18 or > 75 Pregnant Live at altitude > 4000 ft Slept at altitude > 4000 ft within 1 week of study Allergic to acetazolamide, sulfa drugs Taking non‐steroidal anti‐inflammatory drugs, acetazolamide, or corticosteroids 1 week prior to study
Interventions	Day of acetazolamide (acetazolamide 125 mg twice a day, started morning of ascent) or night before acetazolamide (acetazolamide 125 mg twice a day, started evening before ascent)
Outcomes	Primary outcome measures Incidence of acute mountain sickness (time frame: 2 days) by Lake Louise Questionnaire
Starting date	4 August 2018
Contact information	Grant S Lipman, Associate Professor Department of Emergency Medicine, Stanford University, Stanford University
Notes	This study is not yet open for participant recruitment