High Altitude EffectsPhase 4NCT07118462
HighCycle Study: Acetazolamide, High Altitude and Plasma Volume
A Phase 4 study testing Acetazolamide in people with High Altitude Effects and High Altitude Hypoxia, run by Centre d'Expertise sur l'Altitude EXALT at 1 site in Kyrgyzstan.
Trial summary
Each year, millions of people living at low altitude (< 1,000 m) travel to high altitude (≥ 2,500 m) for work, tourism, or sports activities. These individuals are exposed to hypobaric hypoxia, which can trigger acute mountain sickness (AMS)-the most common form of altitude-related illness. Read more about this study
- Who is it for?
- Ages 18 to 44 yearsHealthy volunteers can take part
- Conditions the study is for
- High Altitude Effects, High Altitude Hypoxia, Acute Mountain Sickness (AMS)
- 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
- 270 participants
- Where
- 1 siteKyrgyzstan
- Study dates
- 15 Jul 2024to 31 Dec 2025
- Phase
- Phase 4
- Are there results?
- Not yet: the study is under way
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. Contact the study team or a site near you to ask about taking part.
Kyrgyzstan1 site, 1 recruiting
- Recruiting
National Center for Cardiology and Internal Medicine
Bishkek, 720040
Talant M Sooronbaev, Prof. Dr., +996 312 625679, sooronbaev@yahoo.com
About this study
Official title: HighCycle Study: Effect of Acetazolamide on Plasma Volume During Acute Exposure to High Altitude in Women and Men
Each year, millions of people living at low altitude (< 1,000 m) travel to high altitude (≥ 2,500 m) for work, tourism, or sports activities. These individuals are exposed to hypobaric hypoxia, which can trigger acute mountain sickness (AMS)-the most common form of altitude-related illness. Therefore, understanding the physiological responses to hypoxia that allow acclimatization, as well as the pathophysiology of acute mountain sickness, is of primary importance.
The hematological response to high-altitude exposure initially includes a reduction in plasma volume (PV), leading to an early increase in hemoglobin concentration within the first 24 hours. In contrast, an increase in hemoglobin mass requires several weeks at high altitude. Recent well-controlled physiological studies conducted in hypobaric chambers have demonstrated that this hypoxia-induced PV contraction results from fluid redistribution from the intravascular to the extravascular compartment, rather than from water loss due to increased diuresis.
Prophylaxis of AMS is primarily based on the administration of 250 mg/day of acetazolamide (ACZ), a carbonic anhydrase inhibitor with a mild diuretic effect. Acetazolamide induces metabolic acidosis, which stimulates ventilation and thereby improves oxygenation. The effect of prophylactic ACZ use during high-altitude exposure on PV in lowlanders remains unknown: it is unclear whether ACZ leads to a greater reduction in PV due to its diuretic effect, or to a smaller hypoxia-induced PV contraction as a result of improved oxygenation induced by increased ventilation.
Read the detailed description
Not provided
- Conditions
- High Altitude Effects, High Altitude Hypoxia, Acute Mountain Sickness (AMS), Plasma Volume, Women
- Being tested
- Acetazolamide, Placebo
- Keywords
- acetazolamide, plasma volume, acute mountain sickness, high altitude, hypoxia, women
- 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
Also called Diamox®
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 |
|---|---|---|
| Acetazolamide | Experimental | 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 |
| Placebo | 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.
Plasma volume
Change in plasma volume assessed by the CO-rebreathing method in acetazolamide versus placebo group
Measured: Day 1 at 760 m then Day 2 and Day 3 at 3,600 m.
Secondary outcomes (4)
Plasma volume : sex-related difference
Sex-related differences in the effect of acetazolamide vs.placebo in plasma volume at high altitude.
Measured: Day 1 at 760 m then Day 2 and Day 3 at 3600 m.
Plasma volume : AMS-related difference
Difference in plasma volume change at high altitude between AMS+ and AMS- participants.
Measured: Day 1 at 760 m then Day 2 and Day 3 at 3600 m.
Hormones
Changes in copeptin and midregional proANP serum levels between acetazolamide and placebo group and sex-related difference
Measured: Day 2 at 760 m and Day 2 at 3600 m.
Arterial blood gases
Changes in the arterial blood gases (pH, PaO2, PaCO2, SaO2) between acetazolamide and placebo group.
Measured: Day 2 at 760 m and Day 2 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 Aug 2025
- Study start15 Jul 2024
- Primary completion31 Dec 2025 (estimated)
- Study completion31 Dec 2025 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for High Altitude EffectsStudies of the same condition, open and under way.
- 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
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 270 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Centre d'Expertise sur l'Altitude EXALT
- Sponsor type
- University, hospital or other
- Collaborators
- National Center of Cardiology and Internal Medicine named after academician M.Mirrakhimov, University of Zurich
- Responsible party
- Sponsor
- Investigators
- Michael Furian, Prof. Dr., Study chair, University of ZurichTalant M Sooronbaev, Prof. Dr., Study director, National Center of Cardiology and Internal Medicine, Bishkek, KyrgyzstanPaul Robach, PhD, Principal investigator, EXALT (Centre d'Expertise sur l'Altitude), Grenoble, FranceBenoit Champigneulle, MD, PhD, Principal investigator, EXALT (Centre d'Expertise sur l'Altitude), Grenoble, France
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07118462
- Sponsor's protocol ID
- HighCycle_PV
- Status last verified
- Aug 2025
- First submitted
- 5 Aug 2025
- Last updated
- 12 Aug 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: Only IPD used in the results publication
Study at a glance
From the registry record, last updated by the sponsor on 12 Aug 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- HighCycle Study: Effect of Acetazolamide on Plasma Volume During Acute Exposure to High Altitude in Women and Men
- ClinicalTrials.gov ID
- NCT07118462
- Acronym / sponsor ID
- HighCycle_PV
- Conditions
- High Altitude Effects, High Altitude Hypoxia, Acute Mountain Sickness (AMS), Plasma Volume, Women
- Keywords
- acetazolamide, plasma volume, acute mountain sickness, high altitude, hypoxia, women
- Phase
- Phase 4
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 270 participants (estimated)
- Lead sponsor
- Centre d'Expertise sur l'Altitude EXALTUniversity, hospital or other
- Collaborators
- National Center of Cardiology and Internal Medicine named after academician M.Mirrakhimov, University of Zurich
- Study start
- 15 Jul 2024 (actual)
- Primary completion
- 31 Dec 2025 (estimated)
- Study completion
- 31 Dec 2025 (estimated)
- First posted
- 12 Aug 2025 (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.
Each year, millions of people living at low altitude (< 1,000 m) travel to high altitude (≥ 2,500 m) for work, tourism, or sports activities. These individuals are exposed to hypobaric hypoxia, which can trigger acute mountain sickness (AMS)-the most common form of altitude-related illness. Therefore, understanding the physiological responses to hypoxia that allow acclimatization, as well as the pathophysiology of acute mountain sickness, is of primary importance.
The hematological response to high-altitude exposure initially includes a reduction in plasma volume (PV), leading to an early increase in hemoglobin concentration within the first 24 hours. In contrast, an increase in hemoglobin mass requires several weeks at high altitude. Recent well-controlled physiological studies conducted in hypobaric chambers have demonstrated that this hypoxia-induced PV contraction results from fluid redistribution from the intravascular to the extravascular compartment, rather than from water loss due to increased diuresis.
Prophylaxis of AMS is primarily based on the administration of 250 mg/day of acetazolamide (ACZ), a carbonic anhydrase inhibitor with a mild diuretic effect. Acetazolamide induces metabolic acidosis, which stimulates ventilation and thereby improves oxygenation. The effect of prophylactic ACZ use during high-altitude exposure on PV in lowlanders remains unknown: it is unclear whether ACZ leads to a greater reduction in PV due to its diuretic effect, or to a smaller hypoxia-induced PV contraction as a result of improved oxygenation induced by increased ventilation.
Detailed description
Not provided
Study design
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Acetazolamide | Experimental | 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 |
| Placebo | 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 |
|---|---|---|
| AcetazolamideAlso: Diamox®Administration of 1x125mg acetazolamide in the morning, 1x125mg in the evening, starting 24 hours before departure to 3600 m. | Drug | Acetazolamide |
| PlaceboAdministration of equally looking placebo capsules in the morning and in the evening, starting 24 hours before departure to 3600 m. | Drug | Placebo |
Primary outcome
Plasma volume
Time frame: Day 1 at 760 m then Day 2 and Day 3 at 3,600 m.
Change in plasma volume assessed by the CO-rebreathing method in acetazolamide versus placebo group
4 secondary outcomes
Plasma volume : sex-related difference
Time frame: Day 1 at 760 m then Day 2 and Day 3 at 3600 m.
Plasma volume : AMS-related difference
Time frame: Day 1 at 760 m then Day 2 and Day 3 at 3600 m.
Hormones
Time frame: Day 2 at 760 m and Day 2 at 3600 m.
Arterial blood gases
Time frame: Day 2 at 760 m and Day 2 at 3600 m.
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 12 Aug 2025.
- Individual participant dataSharing planned: Yes. Only IPD used in the results publication
Related trials for High Altitude Effects
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Not yet recruiting
Assessment of Lung Function (Lufu) at Sea Level LA vs. High Altitude HA in Healthy Individuals
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Assessment of Lung Function (Lufu) at Sea Level LA vs. High Altitude HA in Patients With Pulmonary Arterial Hypertension PAH
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Not yet recruiting
Assessment of Total Pulmonary Resistance sPAP/CO Between Sea Level LA vs. High Altitude HA After Re-ascent in Healthy Individuals
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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.
Michael Furian, Prof. Dr. study chair
University of Zurich
Talant M Sooronbaev, Prof. Dr. study director
National Center of Cardiology and Internal Medicine, Bishkek, Kyrgyzstan
Paul Robach, PhD principal investigator
EXALT (Centre d'Expertise sur l'Altitude), Grenoble, France
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 High Altitude Effects and High Altitude Hypoxia, run by Centre d'Expertise sur l'Altitude EXALT 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: looking for participants now, as of the sponsor's last update on 12 Aug 2025. 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?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Benoit Champigneulle, MD PhD (+33476769288, BChampigneulle@chu-grenoble.fr), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Plasma volume (time frame: Day 1 at 760 m then Day 2 and Day 3 at 3,600 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 12 Aug 2025; AzTrials last refreshed its copy on 26 Oct 2026.