A Study of Doravirine/Islatravir in Healthy Lactating Females (MK-8591A-061)

NCT07086079 | Completed Phase 1 FDA Drug

• 2 other identifiers: 8591A-061MK-8591A-061
• Study Type: interventional
• Target: 12
• Locations: 1 country
• Sites: 1

Brief 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.

Conditions

Healthy

Outcome Measures

Primary Outcomes (6)

• 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.

  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.

  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.

  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.

  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.

  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.

  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

  Predose and at designated timepoints up to 24 hours postdose

• Maximum Concentration (Cmax) of DOR in Breast Milk

  Predose and at designated timepoints up to 24 hours postdose

• Time to Maximum Concentration (Tmax) of DOR in Breast Milk

  Predose and at designated timepoints up to 24 hours postdose

• AUC0-24hrs of Total ISL in Breast Milk

  Predose and at designated timepoints up to 24 hours postdose

• Cmax of Total ISL in Breast Milk

  Predose and at designated timepoints up to 24 hours postdose

Study Arms (1)

DOR/ISL

EXPERIMENTAL

Participants will receive DOR/ISL as an oral fixed-dose combination tablet once daily on Days 1 to 7.

Drug: DOR/ISL

Interventions

DOR/ISL DRUG

Oral tablet

Also known as: MK-8591A

DOR/ISL

Eligibility Criteria

• Age: 18 Years+
• Gender Eligibility Details: Healthy Lactating Female Participants
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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

You may not qualify if:

• 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

Sponsors & Collaborators

• Merck Sharp & Dohme LLC: lead

Study Sites (1)

QPS Missouri ( Site 0001)

Springfield, Missouri, 65802, United States

Location

Related Links

• Merck Clinical Trials Information

Study Officials

• Medical Director

  Merck Sharp & Dohme LLC

  STUDY DIRECTOR

Study Design

• Study Type: interventional
• Phase: phase 1
• Allocation: NA
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: SINGLE GROUP
• Sponsor Type: INDUSTRY
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: July 18, 2025
• First Posted: July 25, 2025
• Study Start: September 26, 2025
• Primary Completion: December 8, 2025
• Study Completion: February 4, 2026
• Last Updated: February 20, 2026

Record last verified: 2026-02

Data Sharing

• IPD Sharing: Will share

Locations

US (1)