Acute Mountain SicknessPhase 4NCT06499727
HighCycle Study: Effect of Acetazolamide on Acute Mountain Sickness in Women Compared to Men
A Phase 4 study testing Acetazolamide in people with Acute Mountain Sickness, run by University of Zurich at 1 site in Kyrgyzstan.
Trial summary
Millions of people travel to high altitude for work or leisure activities and are exposed to reduced inspiratory oxygen partial pressure and hypoxemia that may lead to altitude illness, among which the most common form is acute mountain sickness (AMS). Read more about this study
- Who is it for?
- Ages 18 to 44 yearsHealthy volunteers can take part
- Conditions the study is for
- Acute Mountain Sickness
- What is being tested?
- Acetazolamide
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 303 participants
- Where
- 1 siteKyrgyzstan
- Study dates
- 15 Jul 2024to 31 Aug 2025
- Phase
- Phase 4
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 44 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- Healthy, non-smoking men and women, age 18-44 years, without any disease and need of regular medication (including oral contraceptives).
- BMI >18 kg/m2 and <30 kg/m2
- Born, raised and currently living at altitudes <1000 m
- Written informed consent
- Premenopausal women with an eumenorrheic cycle
Who cannot join
- Other types of contraceptvies (contraceptives (hormonal intrauterine device, vaginal ring, subcutaneous injections or implants, among others)
- Pregnancy or nursing
- Anaemic (haemoglobin concentration <10g/dl)
- Any altitude trip <4 weks before the study
- Allergy to acetazolamide and other sulfonamides
Trial locations and contacts
1 site in 1 country.
Kyrgyzstan1 site
National Center for Cardiology and Internal Medicine
Bishkek, Bishkek, 720040
About this study
Official title: HighCycle Study: Effect of Acetazolamide on Acute Mountain Sickness in Women Compared to Men: A Randomized, Placebo-Controlled, Double-Blind Parallel Trial
Millions of people travel to high altitude for work or leisure activities and are exposed to reduced inspiratory oxygen partial pressure and hypoxemia that may lead to altitude illness, among which the most common form is acute mountain sickness (AMS). The main AMS symptoms are headache, malaise, weakness, and fatigue. Prospective studies have shown that 20-60% of newcomers at 2500-4000m develop AMS requiring them to take medications, while, at very high altitudes, AMS may progress to high altitude cerebral oedema. Whether women are more susceptible to AMS remains insufficiently understood since no prospective study controlled for sex hormones, use of hormone contraception or assessed menstrual cycle phase (MCP) at altitude. Therefore, women remain underrepresented and poorly characterized in high altitude studies. In addition, the efficacy and safety of 250 mg/day acetazolamide, the standard recommendation for AMS prevention, has never been compared between sexes, although, women have presumably higher acetazolamide plasma concentration due to lower blood volume. Given the known dose-dependent preventive but also side effects of acetazolamide and equal proportion of women and men among mountain travellers, there is an urgent need to conclusively quantify the efficacy and safety of pre-ventive acetazolamide therapy against AMS in women compared to men.
- Conditions
- Acute Mountain Sickness
- Being tested
- Acetazolamide, Placebo
- Keywords
- Women, Hypoxia, Prevention, Acetazolamide, Altitude
- Medical subject headings
- Altitude Sickness, Hypoxia
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
AcetazolamideDrug
Administration of 1x125mg acetazolamide in the morning, 1x125mg in the evening, starting 24 hours before departure to 3600 m.
PlaceboDrug
Administration of equally looking placebo capsules in the morning and in the evening, starting 24 hours before departure to 3600 m.
| Study group | Role | What they receive |
|---|---|---|
| WOMEN - ACETAZOLAMIDE oral capsule | Active comparator | Acetazolamide 250 mg/day (capsules @125 mg; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. Receives: Drug: Acetazolamide |
| MEN - ACETAZOLAMIDE oral capsule | Active comparator | Acetazolamide 250 mg/day (capsules @125 mg; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. Receives: Drug: Acetazolamide |
| WOMEN - PLACEBO oral capsule | Placebo comparator | Placebo (capsules identically looking as acetazolamide capsules; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. Receives: Drug: Placebo |
| MEN - PLACEBO oral capsule | Placebo comparator | Placebo (capsules identically looking as acetazolamide capsules; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. Receives: Drug: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
Acute Mountain Sickness (AMS) Incidence, LLS 2018
Sex-related difference between acetazolamide and placebo group in the incidence of AMS. AMS incidence will be defined as a Lake Louise Questionnaire version 2018 score of ≥3.
Measured: Day 1 to 3 at 3600 m
Secondary outcomes (8)
Acute Mountain Sickness (AMS) Incidence, LLS 1993
Sex-related difference between acetazolamide and placebo group in the incidence of AMS. AMS incidence will be defined as a Lake Louise Questionnaire version 1993 score of ≥3.
Measured: Day 1 to 3 at 3600 m
Acute Mountain Sickness (AMS) Severity, LLS 2018
Sex-related difference between acetazolamide and placebo group in the AMS severity assessed by the Lake Louise Questionnaire version 2018.
Measured: Day 1 to 3 at 3600 m
Acute Mountain Sickness (AMS) Severity, LLS 1993
Sex-related difference between acetazolamide and placebo group in the AMS severity assessed by the Lake Louise Questionnaire version 1993.
Measured: Day 1 to 3 at 3600 m
Drug-related side effects
Sex-related difference between acetazolamide and placebo group in the incidence and severity of medication side effects.
Measured: Day 1 to 3 at 3600 m
Arterial blood gases
Sex-related differences between acetazolamide and placebo group in the arterial blood gases (pH, PaO2, PaCO2, SaO2).
Measured: Day 2 at 760 m and day 2 at 3600 m
Acetazolamide plasma concentration
Sex-related differences between acetazolamide plasma concentration assessed by dried blood spots.
Measured: Day 2 at 3600 m
Hypoxic ventilatory response
Sex-related difference in the hypoxic ventilatory response assessed under FiO2 of 0.115 and while cycling on a bicycle at 30% of predicted maximal work capacity.
Measured: Day 2 at 760 m
Perceived pain visualization
Sex-related differences between acetazolamide and placebo group on perceived pain sensations, visualized by the SMaRT tablet app
Measured: Day 1 to 3 at 3600 m
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted12 Jul 2024
- Study start15 Jul 2024
- Primary completion31 Aug 2025
- Study completion31 Aug 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Acute Mountain SicknessStudies of the same condition, open and under way.
- More trials run by University of ZurichThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 4
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 303 participants (actual)
Sponsor and investigators
- Lead sponsor
- University of Zurich
- Sponsor type
- University, hospital or other
- Collaborators
- National Center of Cardiology and Internal Medicine named after academician M.Mirrakhimov, University Hospital Heidelberg, Laboratoire des Adaptations Métaboliques à l'Exercice en conditions Physiologiques et Pathologiques
- Responsible party
- Sponsor
- Investigators
- Michael Furian, Prof. Dr., Study chair, University of ZurichTalant Sooronbaev, Prof. Dr., Study director, National Center of Cardiology and Internal Medicine, Bishkek, Kyrgyzstan
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06499727
- Sponsor's protocol ID
- HighCycle_AMS
- Status last verified
- May 2025
- First submitted
- 5 Jul 2024
- Last updated
- 23 Jan 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided
Study at a glance
From the registry record, last updated by the sponsor on 23 Jan 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- HighCycle Study: Effect of Acetazolamide on Acute Mountain Sickness in Women Compared to Men: A Randomized, Placebo-Controlled, Double-Blind Parallel Trial
- ClinicalTrials.gov ID
- NCT06499727
- Acronym / sponsor ID
- HighCycle_AMS
- Conditions
- Acute Mountain Sickness
- Keywords
- Women, Hypoxia, Prevention, Acetazolamide, Altitude
- Phase
- Phase 4
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 303 participants (actual)
- Lead sponsor
- University of ZurichUniversity, hospital or other
- Collaborators
- National Center of Cardiology and Internal Medicine named after academician M.Mirrakhimov, University Hospital Heidelberg, Laboratoire des Adaptations Métaboliques à l'Exercice en conditions Physiologiques et Pathologiques
- Study start
- 15 Jul 2024 (actual)
- Primary completion
- 31 Aug 2025 (actual)
- Study completion
- 31 Aug 2025 (actual)
- First posted
- 12 Jul 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
Millions of people travel to high altitude for work or leisure activities and are exposed to reduced inspiratory oxygen partial pressure and hypoxemia that may lead to altitude illness, among which the most common form is acute mountain sickness (AMS). The main AMS symptoms are headache, malaise, weakness, and fatigue. Prospective studies have shown that 20-60% of newcomers at 2500-4000m develop AMS requiring them to take medications, while, at very high altitudes, AMS may progress to high altitude cerebral oedema. Whether women are more susceptible to AMS remains insufficiently understood since no prospective study controlled for sex hormones, use of hormone contraception or assessed menstrual cycle phase (MCP) at altitude. Therefore, women remain underrepresented and poorly characterized in high altitude studies. In addition, the efficacy and safety of 250 mg/day acetazolamide, the standard recommendation for AMS prevention, has never been compared between sexes, although, women have presumably higher acetazolamide plasma concentration due to lower blood volume. Given the known dose-dependent preventive but also side effects of acetazolamide and equal proportion of women and men among mountain travellers, there is an urgent need to conclusively quantify the efficacy and safety of pre-ventive acetazolamide therapy against AMS in women compared to men.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 4
| Arm | Type | Receives |
|---|---|---|
| WOMEN - ACETAZOLAMIDE oral capsule | Active comparator | Drug: AcetazolamideAcetazolamide 250 mg/day (capsules @125 mg; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. |
| MEN - ACETAZOLAMIDE oral capsule | Active comparator | Drug: AcetazolamideAcetazolamide 250 mg/day (capsules @125 mg; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. |
| WOMEN - PLACEBO oral capsule | Placebo comparator | Drug: PlaceboPlacebo (capsules identically looking as acetazolamide capsules; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. |
| MEN - PLACEBO oral capsule | Placebo comparator | Drug: PlaceboPlacebo (capsules identically looking as acetazolamide capsules; 1 in the morning, 1 in the evening), orally. Medication starts 24 hours before ascent to 3600 m until the morning after the second night at 3600 m. |
Who may qualify
- Ages
- 18 to 44 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (5 listed)
- Healthy, non-smoking men and women, age 18-44 years, without any disease and need of regular medication (including oral contraceptives).
- BMI >18 kg/m2 and <30 kg/m2
- Born, raised and currently living at altitudes <1000 m
- Written informed consent
- Premenopausal women with an eumenorrheic cycle
Key exclusion criteria (5 listed)
- Other types of contraceptvies (contraceptives (hormonal intrauterine device, vaginal ring, subcutaneous injections or implants, among others)
- Pregnancy or nursing
- Anaemic (haemoglobin concentration <10g/dl)
- Any altitude trip <4 weks before the study
- Allergy to acetazolamide and other sulfonamides
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| AcetazolamideAdministration of 1x125mg acetazolamide in the morning, 1x125mg in the evening, starting 24 hours before departure to 3600 m. | Drug | MEN - ACETAZOLAMIDE oral capsule, WOMEN - ACETAZOLAMIDE oral capsule |
| PlaceboAdministration of equally looking placebo capsules in the morning and in the evening, starting 24 hours before departure to 3600 m. | Drug | MEN - PLACEBO oral capsule, WOMEN - PLACEBO oral capsule |
Primary outcome
Acute Mountain Sickness (AMS) Incidence, LLS 2018
Time frame: Day 1 to 3 at 3600 m
Sex-related difference between acetazolamide and placebo group in the incidence of AMS. AMS incidence will be defined as a Lake Louise Questionnaire version 2018 score of ≥3.
8 secondary outcomes
Acute Mountain Sickness (AMS) Incidence, LLS 1993
Time frame: Day 1 to 3 at 3600 m
Acute Mountain Sickness (AMS) Severity, LLS 2018
Time frame: Day 1 to 3 at 3600 m
Acute Mountain Sickness (AMS) Severity, LLS 1993
Time frame: Day 1 to 3 at 3600 m
Drug-related side effects
Time frame: Day 1 to 3 at 3600 m
Arterial blood gases
Time frame: Day 2 at 760 m and day 2 at 3600 m
Acetazolamide plasma concentration
Time frame: Day 2 at 3600 m
Hypoxic ventilatory response
Time frame: Day 2 at 760 m
Perceived pain visualization
Time frame: Day 1 to 3 at 3600 m
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 23 Jan 2026.
- Individual participant dataSharing planned: Undecided
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Michael Furian, Prof. Dr. study chair
University of Zurich
Talant Sooronbaev, Prof. Dr. study director
National Center of Cardiology and Internal Medicine, Bishkek, Kyrgyzstan
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 4 study testing Acetazolamide in people with Acute Mountain Sickness, run by University of Zurich at 1 site in Kyrgyzstan.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 5 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 23 Jan 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Kyrgyzstan. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 4 studies take place after a treatment is approved, to learn more about its long-term benefits and risks in everyday use.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Acute Mountain Sickness (AMS) Incidence, LLS 2018 (time frame: Day 1 to 3 at 3600 m). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 23 Jan 2026.