HealthyPhase 1NCT07086079
A Study of Doravirine/Islatravir in Healthy Lactating Females (MK-8591A-061)
A Phase 1 study testing DOR/ISL in people with Healthy, run by Merck Sharp & Dohme LLC at 1 site in United States.
Trial summary
The goal of this study is to learn what happens to doravirine (DOR) and islatravir (ISL) in a healthy lactating female's body over time. Researchers want to learn if DOR and ISL are in breast milk. Read more about this study
- Who is it for?
- Ages 18 years and older, women onlyHealthy volunteers can take part
- Conditions the study is for
- Healthy
- What is being tested?
- DOR/ISL
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 12 participants
- Where
- 1 siteUnited States
- Study dates
- 26 Sep 2025to 4 Feb 2026
- Phase
- Phase 1
- 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 years and older
- Women only
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- The main inclusion criteria include but are not limited to the following:
- Is at least 6-weeks postpartum at the time of administration of study drug, following the delivery of a healthy singleton neonate
- Is willing and able to express breast milk using an electric pump prior to study drug administration and is expected to be able to express at least 4 times over a 24-hour period after study drug administration
Who cannot join
- The main exclusion criteria include but are not limited to the following:
- Has a history of clinically significant endocrine, gastrointestinal, cardiovascular, hematological, hepatic, immunological, renal, respiratory, genitourinary, psychiatric, or major neurological (including stroke and chronic seizures) abnormalities or diseases
- Has had mastitis within 30 days prior to administration of study drug
Trial locations and contacts
1 site in 1 country.
United States1 site
QPS Missouri ( Site 0001)
Springfield, Missouri, 65802
About this study
Official title: A Clinical Study to Evaluate the Breast Milk and Plasma Pharmacokinetics of MK-8591A in Healthy Lactating Female Participants
The goal of this study is to learn what happens to doravirine (DOR) and islatravir (ISL) in a healthy lactating female's body over time. Researchers want to learn if DOR and ISL are in breast milk.
- Conditions
- Healthy
- Being tested
- DOR/ISL
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
DOR/ISLDrug
Also called MK-8591A
Oral tablet
| Study group | Role | What they receive |
|---|---|---|
| DOR/ISL | Experimental | Participants will receive DOR/ISL as an oral fixed-dose combination tablet once daily on Days 1 to 7. Receives: Drug: DOR/ISL |
What is being measured
The primary outcome is the main question the study is designed to answer.
Cumulative Amount of DOR Excreted in Breast Milk From 0 to 24 Hours (Ae0-24hrs)
Breast milk samples will be collected to determine the Ae0-24hrs after administration of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
Body Weight Normalized Infant Theoretical Dose of DOR
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of DOR as normalized by participant-reported infant body weight.
Measured: Predose and at designated timepoints up to 24 hours postdose
Relative Infant Theoretical Dose of DOR
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of DOR relative to the maternal dose.
Measured: Predose and at designated timepoints up to 24 hours postdose
Cumulative Amount of Total ISL Excreted in Breast Milk From 0 to 24 Hours (Ae0-24hrs)
Breast milk samples will be collected to determine the Ae0-24hrs after administration of total ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
Body Weight Normalized Infant Theoretical Dose of ISL
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of ISL as normalized by participant-reported infant body weight.
Measured: Predose and at designated timepoints up to 24 hours postdose
Relative Infant Theoretical Dose of ISL
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of ISL relative to the maternal dose.
Measured: Predose and at designated timepoints up to 24 hours postdose
Secondary outcomes (14)
Area Under the Concentration-Time Curve From 0 to 24 Hours (AUC0-24hrs) of DOR in Breast Milk
Breast milk samples will be collected to determine the AUC0-24hrs of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
Maximum Concentration (Cmax) of DOR in Breast Milk
Breast milk samples will be collected to determine the Cmax of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
Time to Maximum Concentration (Tmax) of DOR in Breast Milk
Breast milk samples will be collected to determine the Tmax of DOR
Measured: Predose and at designated timepoints up to 24 hours postdose
AUC0-24hrs of Total ISL in Breast Milk
Breast milk samples will be collected to determine the AUC0-24hrs of total ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
Cmax of Total ISL in Breast Milk
Breast milk samples will be collected to determine the Cmax of total ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
Tmax of Total ISL in Breast Milk
Breast milk samples will be collected to determine the Tmax of total ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
AUC0-24hrs of DOR in Plasma
Plasma samples will be collected to determine the AUC0-24hrs of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
Cmax of DOR in Plasma
Plasma samples will be collected to determine the Cmax of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
Tmax of DOR in Plasma
Plasma samples will be collected to determine the Tmax of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
Concentration at 24 Hours (C24) of DOR in Plasma
Plasma samples will be collected to determine the C24 of DOR.
Measured: Predose and at designated timepoints up to 24 hours postdose
AUC0-24hrs of ISL in Plasma
Plasma samples will be collected to determine the AUC0-24hrs of ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
Cmax of ISL in Plasma
Plasma samples will be collected to determine the Cmax of ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
Tmax of ISL in Plasma
Plasma samples will be collected to determine the Tmax of ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
C24 of ISL in Plasma
Plasma samples will be collected to determine the C24 of ISL.
Measured: Predose and at designated timepoints up to 24 hours postdose
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted25 Jul 2025
- Study start26 Sep 2025
- Primary completion8 Dec 2025
- Study completion4 Feb 2026
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for HealthyStudies of the same condition, open and under way.
- More trials run by Merck Sharp & Dohme LLCThe 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 1
- Primary purpose
- Basic science
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Enrolment
- 12 participants (actual)
Sponsor and investigators
- Lead sponsor
- Merck Sharp & Dohme LLC
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
- Investigators
- Medical Director, Study director, Merck Sharp & Dohme LLC
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07086079
- Sponsor's protocol ID
- 8591A-061
- Other IDs
- MK-8591A-061
- Status last verified
- Feb 2026
- First submitted
- 18 Jul 2025
- Last updated
- 20 Feb 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- Yes: https://trialstransparency.msdclinicaltrials.com/pdf/ProcedureAccessClinicalTrialData.pdf
Study at a glance
From the registry record, last updated by the sponsor on 20 Feb 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A Clinical Study to Evaluate the Breast Milk and Plasma Pharmacokinetics of MK-8591A in Healthy Lactating Female Participants
- ClinicalTrials.gov ID
- NCT07086079
- Acronym / sponsor ID
- 8591A-061
- Conditions
- Healthy
- Phase
- Phase 1
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 12 participants (actual)
- Lead sponsor
- Merck Sharp & Dohme LLCIndustry (pharma, biotech, devices)
- Study start
- 26 Sep 2025 (actual)
- Primary completion
- 8 Dec 2025 (actual)
- Study completion
- 4 Feb 2026 (actual)
- First posted
- 25 Jul 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.
The goal of this study is to learn what happens to doravirine (DOR) and islatravir (ISL) in a healthy lactating female's body over time. Researchers want to learn if DOR and ISL are in breast milk.
Study design
- Primary purpose
- Basic science
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| DOR/ISL | Experimental | Drug: DOR/ISLParticipants will receive DOR/ISL as an oral fixed-dose combination tablet once daily on Days 1 to 7. |
Who may qualify
- Ages
- 18 years and older
- Sex
- Female only
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (3 listed)
- Is at least 6-weeks postpartum at the time of administration of study drug, following the delivery of a healthy singleton neonate
- Is willing and able to express breast milk using an electric pump prior to study drug administration and is expected to be able to express at least 4 times over a 24-hour period after study drug administration
Key exclusion criteria (3 listed)
- Has a history of clinically significant endocrine, gastrointestinal, cardiovascular, hematological, hepatic, immunological, renal, respiratory, genitourinary, psychiatric, or major neurological (including stroke and chronic seizures) abnormalities or diseases
- Has had mastitis within 30 days prior to administration of study drug
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 |
|---|---|---|
| DOR/ISLAlso: MK-8591AOral tablet | Drug | DOR/ISL |
Primary outcome
Cumulative Amount of DOR Excreted in Breast Milk From 0 to 24 Hours (Ae0-24hrs)
Time frame: Predose and at designated timepoints up to 24 hours postdose
Breast milk samples will be collected to determine the Ae0-24hrs after administration of DOR.
Body Weight Normalized Infant Theoretical Dose of DOR
Time frame: Predose and at designated timepoints up to 24 hours postdose
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of DOR as normalized by participant-reported infant body weight.
Relative Infant Theoretical Dose of DOR
Time frame: Predose and at designated timepoints up to 24 hours postdose
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of DOR relative to the maternal dose.
Cumulative Amount of Total ISL Excreted in Breast Milk From 0 to 24 Hours (Ae0-24hrs)
Time frame: Predose and at designated timepoints up to 24 hours postdose
Breast milk samples will be collected to determine the Ae0-24hrs after administration of total ISL.
Body Weight Normalized Infant Theoretical Dose of ISL
Time frame: Predose and at designated timepoints up to 24 hours postdose
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of ISL as normalized by participant-reported infant body weight.
Relative Infant Theoretical Dose of ISL
Time frame: Predose and at designated timepoints up to 24 hours postdose
Breast milk samples will be collected to calculate the theoretical daily (24 hour) infant dose of ISL relative to the maternal dose.
14 secondary outcomes
Area Under the Concentration-Time Curve From 0 to 24 Hours (AUC0-24hrs) of DOR in Breast Milk
Time frame: Predose and at designated timepoints up to 24 hours postdose
Maximum Concentration (Cmax) of DOR in Breast Milk
Time frame: Predose and at designated timepoints up to 24 hours postdose
Time to Maximum Concentration (Tmax) of DOR in Breast Milk
Time frame: Predose and at designated timepoints up to 24 hours postdose
AUC0-24hrs of Total ISL in Breast Milk
Time frame: Predose and at designated timepoints up to 24 hours postdose
Cmax of Total ISL in Breast Milk
Time frame: Predose and at designated timepoints up to 24 hours postdose
Tmax of Total ISL in Breast Milk
Time frame: Predose and at designated timepoints up to 24 hours postdose
AUC0-24hrs of DOR in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
Cmax of DOR in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
Tmax of DOR in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
Concentration at 24 Hours (C24) of DOR in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
AUC0-24hrs of ISL in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
Cmax of ISL in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
Tmax of ISL in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
C24 of ISL in Plasma
Time frame: Predose and at designated timepoints up to 24 hours postdose
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 20 Feb 2026.
- Merck Clinical Trials InformationLink provided by the sponsor.
- Individual participant dataSharing planned: Yes. https://trialstransparency.msdclinicaltrials.com/pdf/ProcedureAccessClinicalTrialData.pdf
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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.
Medical Director study director
Merck Sharp & Dohme LLC
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 1 study testing DOR/ISL in people with Healthy, run by Merck Sharp & Dohme LLC at 1 site in United States.
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 3 inclusion and 3 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 20 Feb 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 United States. 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 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.
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?
Cumulative Amount of DOR Excreted in Breast Milk From 0 to 24 Hours (Ae0-24hrs) (time frame: Predose and at designated timepoints up to 24 hours postdose). The study lists 6 primary outcomes in all. 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 20 Feb 2026.