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HIV Preexposure ProphylaxisPhase 3Impower-024NCT04652700

Oral Islatravir (MK-8591) Once-Monthly as Preexposure Prophylaxis (PrEP) in Men and Transgender Women Who Are at High Risk for HIV-1 Infection (MK-8591-024)

A Phase 3 study testing ISL, FTC/TDF and FTC/TAF in people with HIV Preexposure Prophylaxis, run by Merck Sharp & Dohme LLC at 25 sites in 7 countries.

Terminated

Stopped early. The study ended before it was planned to and will not resume.

Official record
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Trial summary

The main purpose of the study is to evaluate the safety and tolerability of oral Islatravir (ISL) once monthly (QM) as Preexposure Prophylaxis (PrEP) in cisgender men who have sex with men (MSM) and transgender women (TGW) who have sex with men and who are at high risk of HIV-1 infection with 48 or 96 weeks of… Read more about this study

Who is it for?
Ages 16 years and older, men onlyHealthy volunteers can take part
Conditions the study is for
HIV Preexposure Prophylaxis
What is being tested?
ISL, FTC/TDF and FTC/TAF
Type of treatment
Pill or oral medicine
Could I receive a placebo?
Yes, some participants may receive a placebo
How many people
494 participants
Where
25 sitesin 7 countries
Study dates
15 Mar 2021to 4 Aug 2023
Phase
Phase 3
Are there results?
Yes, posted in the registrySummary in the doctors' view

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 16 years and older
  • Men only
  • Healthy volunteers accepted
  • Child, Adult, Older adult

Who may be able to join

  • Has confirmed Human Immunodeficiency Virus (HIV) uninfected based on negative HIV-1/HIV-2 test result before randomization
  • Is sexually active with male or transgender women (TGW) partners defined as having anal sexual intercourse with a man or TGW at least once in the past month
  • Is at high risk for sexually acquiring HIV-1 infection based on self-report of at least 1 of the following: a) Condomless receptive anal intercourse in the 6 months prior to screening occurring outside a mutually monogamous HIV seronegative concordant relationship b) More than 5 partners (anal intercourse) in the 6 months prior to screening c) Any unprescribed stimulant drug use in the 6 months prior to screening d) Rectal or urethral gonorrhea or chlamydia or incident syphilis in the 6 months prior to screening
  • Participants 16 or 17 years of age must weigh ≥35 kg. Enrollment for 16- to 17-year-old participants will begin only after completion of the Sentinel Cohort IA and review of IA results by the external data monitoring committee (eDMC)
  • Has no plans to relocate or travel away from the site for ≥4 consecutive weeks during study participation

Who cannot join

  • Has hypersensitivity or other contraindication to any component of the study interventions as determined by the investigator
  • Has chronic HBV infection or past HBV infection which could indicate risk for Hepatitis B reactivation
  • Has known current or chronic history of liver disease or known hepatic or biliary abnormalities, unless the participant has stable liver function tests and no evidence of hepatic synthetic dysfunction
  • Has a history of malignancy within 5 years of screening except for adequately treated basal cell or squamous cell skin cancer or in situ anal cancers
  • Has a history or current evidence of any condition, therapy, laboratory abnormality or other circumstance that might, in the opinion of the investigator, confound the results of the study or interfere with the participant's participation for the full duration of the study, such that it is not in the best interest of the participant to enroll
  • Has taken cabotegravir, lenacapavir, or any other long-acting HIV prevention product at any time
Show all 9Show fewer
  • Is currently receiving or is anticipated to require any prohibited therapies outlined in the study from 30 days prior to Day 1 through the duration of the study
  • Is currently participating in or has participated in an interventional or prevention clinical study with an investigational compound or device, within 30 days prior to Day 1 through the duration of the study
  • Has exclusionary laboratory values within 45 days prior to Day 1

Trial locations and contacts

25 sites in 7 countries.

25 sites in 7 countries

United States15 sites
  • Ponce De Leon Center Grady Health ( Site 0032)

    Atlanta, Georgia, 30308

  • Central Texas Clinical Research ( Site 0002)

    Austin, Texas, 78705

  • University of Alabama at Birmingham-UAB 1917 Research Clinic ( Site 0007)

    Birmingham, Alabama, 35222

  • The University of North Carolina at Chapel Hill ( Site 0019)

    Chapel Hill, North Carolina, 27599

  • Howard Brown Health Center ( Site 0004)

    Chicago, Illinois, 60613

  • Midway Immunology and Research Center ( Site 0014)

    Ft. Pierce, Florida, 34982

  • The Crofoot Research Center ( Site 0025)

    Houston, Texas, 77098

  • The University of Mississippi Medical Center ( Site 0012)

    Jackson, Mississippi, 39216

  • UCLA Center for Clinical AIDS Research and Education ( Site 0011)

    Los Angeles, California, 90035

  • Global Research Institute ( Site 0031)

    Los Angeles, California, 90036

  • University of Miami Miller School of Medicine-Infectious Disease ( Site 0029)

    Miami, Florida, 33136

  • Rutgers New Jersey Medical School-Clinical Research Center ( Site 0017)

    Newark, New Jersey, 07103

  • Orlando Immunology Center ( Site 0010)

    Orlando, Florida, 32803

  • Bridge HIV - San Francisco Department of Public Health ( Site 0003)

    San Francisco, California, 94102

  • The GW Medical Faculty Associates-Medicine ( Site 0033)

    Washington D.C., District of Columbia, 20037

Other trials in United States

South Africa3 sites
  • Desmond Tutu HIV Foundation ( Site 0202)

    Cape Town, Western Cape, 7925

  • Perinatal HIV Research Unit (PHRU)-HIV Prevention CRS ( Site 0203)

    Johannesburg, Gauteng, 1864

  • Wits Reproductive Health and HIV Institute (WRHI)-Research Center ( Site 0201)

    Johannesburg, Gauteng, 2000

Other trials in South Africa

Thailand3 sites
  • Chulalongkorn University-Pediatrics ( Site 0051)

    Bangkok, Bangkok, 10330

  • HIV Netherlands Australia Thailand Research Collaboration ( Site 0056)

    Bangkok, Bangkok, 10330

  • Research Institute for Health Sciences-Research Institute for Health Sciences Building 1 ( Site 0052

    Chiang Mai, 50200

Other trials in Thailand

Brazil1 site
  • Centro de Referência e Treinamento DST/AIDS ( Site 0351)

    São Paulo, 04121-000

Other trials in Brazil

France1 site
  • Hôpital Saint-Louis-Infectious Diseases and tropical diseases ( Site 0151)

    Paris, Île-de-France Region, 75010

Other trials in France

Japan1 site
  • Center Hospital of the National Center for Global Health and Medicine ( Site 0101)

    Shinjyuku-ku, Tokyo, 162-8655

Other trials in Japan

Peru1 site
  • Via Libre ( Site 0404)

    Lima, 15001

Other trials in Peru

About this study

Official title: A Phase 3, Randomized, Active-Controlled, Double-Blind Clinical Study to Evaluate the Efficacy and Safety of Oral Islatravir Once-Monthly as Preexposure Prophylaxis in Cisgender Men and Transgender Women Who Have Sex With Men, and Are at High Risk for HIV-1 Infection

The main purpose of the study is to evaluate the safety and tolerability of oral Islatravir (ISL) once monthly (QM) as Preexposure Prophylaxis (PrEP) in cisgender men who have sex with men (MSM) and transgender women (TGW) who have sex with men and who are at high risk of HIV-1 infection with 48 or 96 weeks of treatment and a minimum follow-up of 42 days.

Read the detailed description

Based on laboratory findings of decreased lymphocyte and CD4+ T-cell counts across the islatravir program, dosing of blinded study intervention was halted on 13-Dec-2021. Blinded assessments conducted prior to then are designated as Study Part 1. During Study Part 2, participants from Part 1 were switched to PrEP therapy with emtricitabine/tenofovir disoproxil (FTC/TDF) or emtricitabine/tenofovir alafenamide (FTC/TAF) while continuing in the study, but participants, investigators, and Sponsor personnel remained blinded to the Part 1 treatment. In Part 3, participants, investigators, and all Sponsor personnel are unblinded to participant's original randomized intervention group, and participants may continue to receive unblinded FTC/TDF or FTC/TAF.

Being tested
ISL, FTC/TDF, FTC/TAF, Placebo to ISL, Placebo to FTC/TDF
Keywords
Preexposure prophylaxis (PrEP), Prevention

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • ISLDrug

    Also called MK-8591

    ISL 60 mg tablet, QM, orally for up to 24 months

  • FTC/TDFDrug

    Also called Truvada, Emtricitabine/Tenofovir Disoproxil Fumarate

    Participants receive 200/245 mg of FTC/TDF combination tablet, QD, orally for up to 24 months

  • FTC/TAFDrug

    Also called Descovy, Emtricitabine/Tenofovir Alafenamide

    Participants receive 200/25 mg of FTC/TAF combination tablet, QD, orally for up to 24 months

  • Placebo to ISLDrug

    Placebo ISL 0 mg tablets QM, orally for up to 24 months.

  • Placebo to FTC/TDFDrug

    Placebo FTC/TDF 0 mg tablets QD, orally for up to 24 months

  • Placebo to FTC/TAFDrug

    Placebo FTC/TAF 0 mg tablets QD, orally for up to 24 months

Study groups in NCT04652700
Study groupRoleWhat they receive
Islatravir (ISL) Once Monthly (QM) GroupExperimentalParticipants receive 60 mg tablet of ISL QM, orally plus Placebo to Emtricitabine/Tenofovir Disoproxil Fumarate (FTC/TDF) tablet once daily (QD) or Placebo to Emtricitabine/Tenofovir Alafenamide (FTC/TAF) tablet QD, orally for up to 24 months of treatment duration.
Receives: Drug: ISL; Drug: Placebo to FTC/TDF; Drug: Placebo to FTC/TAF
FTC/TDF or FTC/TAF QD GroupActive comparatorParticipants receive 200/245 mg or 200/300 mg of FTC/TDF combination tablet, QD, orally or 200/25 mg of FTC/TAF combination tablet, QD, orally at investigator's discretion plus Placebo to ISL tablet QM, orally for up to 24 months of treatment duration.
Receives: Drug: FTC/TDF; Drug: FTC/TAF; Drug: Placebo to ISL

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Number of Participants Who Experienced an Adverse Event (AE) During Blinded Treatment

    An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. The number of participants who experienced an AE will be reported for each treatment arm.

    Measured: Up to approximately 10.5 months

  2. Number of Participants Who Discontinued From Blinded Study Treatment Due to an AE

    An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. The number of participants who experienced an AE will be reported for each treatment arm.

    Measured: Up to approximately 9 months

Secondary outcomes (1)
  1. Number of Participants With Confirmed HIV-1 Infection

    The number of participants with confirmed HIV-1 infections during the blinded treatment period is presented.

    Measured: Up to approximately 10.5 months

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted3 Dec 2020
  2. Study start15 Mar 2021
  3. Primary completion4 Aug 2023
  4. Study completion4 Aug 2023

Why it stopped: Voluntarily terminated due to benefit/risk assessment.

Resources

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 3
Primary purpose
Prevention
Allocation
Randomised
Intervention model
Parallel groups
Masking
Double blind
Who is masked
Participant, Investigator
Enrolment
494 participants (actual)
IDs, dates and publications
ClinicalTrials.gov ID
NCT04652700
Sponsor's protocol ID
8591-024
Other IDs
MK-8591-024, jRCT2031200419, 2020-003309-79
Acronym
Impower-024
Status last verified
Apr 2026
First submitted
2 Dec 2020
Last updated
5 May 2026
Data monitoring committee
Yes
FDA-regulated drug
Yes
FDA-regulated device
No
Individual data sharing
Yes: http://engagezone.msd.com/doc/ProcedureAccessClinicalTrialData.pdf

Publications

  • Landovitz RJ, Pinedo Y, Hinestrosa F, Crofoot GE, Brinson C, Buchbinder S, Molina JM, Gravett RM, Brock JB, Ramgopal MN, Rosengren AL, Ofotokun I, Valdez Madruga J, Liegeon G, Panchia R, Supparatpinyo K, Avihingsanon A, Creticos C, Swaminathan S, Doblecki-Lewis S, Rodriguez J, Siegel M, Oka S, Puthanakit T, Grinsztejn B, Sanders EJ, Lama JR, Lombaard J, Ndlovu N, Hwang P, Du J, Jackson B, Homony B, Evans B, Sklar P, Robertson MN, Plank RM. Safety and Tolerability of Oral Islatravir Once Monthly as Pre-Exposure Prophylaxis in Cisgender Men and Transgender Women Who Have an Elevated Likelihood of HIV-1 Exposure: Results From the IMPOWER-24 Randomized Phase 3 Study. Clin Infect Dis. 2026 Mar 14:ciag171. doi: 10.1093/cid/ciag171. Online ahead of print.

    PubMed 41830344

Questions about this trial

What is this clinical trial studying?

A Phase 3 study testing ISL, FTC/TDF and FTC/TAF in people with HIV Preexposure Prophylaxis, run by Merck Sharp & Dohme LLC at 25 sites in 7 countries.

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 9 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: stopped early, as of the sponsor's last update on 5 May 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 25 sites in United States, South Africa, Thailand, Brazil, France and 2 more countries. 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. 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 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 11 Dec 2024). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

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?

Number of Participants Who Experienced an Adverse Event (AE) During Blinded Treatment (time frame: Up to approximately 10.5 months). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT04652700, which also lists 1 linked publication.

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 5 May 2026.

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