Recent Updates
Recently added Catalysts

MK-8591A

Phase 3

HIV-1 Infection | Small molecule | Infectious Disease |Merck & Company, Inc.|Last Updated: Dec 23, 2025

Success Probability

Subscribe to view

Market & Valuation

Subscribe to view

Trial Design

UNCONTROLLED
Total Trials1
Total Enrollment2,000

FDA Designations

No designations recorded

Clinical trial landscape

MK-8591A · 2 trials · 2 indications

Phase 3 1Phase 1 1
NCT04776252Open-label, Follow-up of Doravirine/Islatravir (DOR/ISL 100 mg/0.75mg) for Participants With Human Immunodeficiency Virus-1 (HIV-1) Infection (MK-8591A-033)HIV-1 Infection
ACTIVE NOT_RECRUITING2,000 Analytics
PHASE3ACTIVE NOT_RECRUITING
Open-label, Follow-up of Doravirine/Islatravir (DOR/ISL 100 mg/0.75mg) for Participants With Human Immunodeficiency Virus-1 (HIV-1) Infection (MK-8591A-033)
HIV-1 InfectionUnlock trial analytics

Study Endpoints

Primary Endpoints

Participants with serious adverse events (SAEs)
Up to Week 198

Percentage of participants with serious adverse events (SAEs)

Participants who discontinued due to an adverse event (AE)
Up to Week 192

Percentage of participants who discontinued study treatment due to an AE.

Area under the curve from time 0-infinity (AUC0-inf) of DOR
At designated time points up to ~30 days

AUC0-inf is a measure of plasma drug concentration from time 0 to infinity and is estimated as the area under the plot of plasma concentration against time 0 to infinity after drug administration. Blood samples collected at designated time points will be used to determine the AUC0-inf of DOR.

Area under the curve from time 0 to last measurable concentration (AUC0-last) of Doravine
At designated time points up to ~30 days

AUC0-last is defined as the area under the concentration-time curve from time 0 to time of last measurable concentration of DOR. Blood will be collected at designated time points to determine the AUC0-last of DOR.

Maximum plasma concentration (Cmax) of doravine
At designated time points up to ~30 days

Cmax is the maximum concentration of the drug observed in plasma. Blood samples collected at designated time points will be used to determine Cmax of DOR.

Plasma concentration at 24 hours postdose (C24) of DOR
At designated time points up to ~24 hours postdose

C24 is the concentration at 24 hours postdose of the drug observed in plasma. Blood samples collected at 24 postdose will be used to determine C24 of DOR.

AUC0-inf of ISL
At designated time points up to ~30 days

AUC0-inf is a measure of plasma drug concentration and time 0 to infinity and is estimated as the area under the plot of plasma concentration against time 0 to infinity after drug administration. Blood samples collected at designated time points will be used to determine the AUC0-inf of ISL.

AUC0-last of ISL
At designated time points up to ~30 days

AUC0-last is defined as the area under the concentration-time curve from time zero to time of last measurable concentration of ISL. Blood will be collected at designated time points to determine the AUC0-last of ISL.

Cmax of ISL
At designated time points up to ~30 days

Cmax is the maximum concentration of the drug observed in plasma. Blood samples collected at designated time points will be used to determine Cmax of ISL.

Secondary Endpoints

Number of participants who experienced an adverse event (AE)
Up to ~44 days
Number of participants who discontinued study intervention due to an AE
Up to ~30 days
Unlock Study Endpoints

Study Design & Arms

AllocationNA
MaskingNONE
ModelSINGLE_GROUP
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
MK-8591AEXPERIMENTALFixed dose combination (FDC) tablet of 100 mg doravirine, 0.75 mg islatravir taken orally, once daily for up to 192 weeks.
MK-8591A Sequence 1AEXPERIMENTALParticipants will receive Doravine/Islatravir (DOR/ISL) fixed-dose combination (FDC) tablet under fasting conditions followed by a DOR/ISL FDC tablet under fed conditions followed by a single dose Doravine tablet and a single dose Islatravir capsule under fasting conditions.
MK-8591A Sequence 2AEXPERIMENTALParticipants will receive DOR/ISL FDC tablet under fasting conditions followed by a single dose DOR tablet and a single dose ISL capsule under fasting conditions followed by DOR/ISL FDC tablet under fed conditions.
MK-8591A Sequence 1BEXPERIMENTALParticipants will receive DOR/ISL FDC tablet under fed conditions followed by a DOR/ISL FDC tablet under fasting conditions followed by a single dose DOR tablet and a single dose ISL capsule under fasting conditions.
MK-8591A Sequence 2BEXPERIMENTALParticipants will receive DOR/ISL FDC tablet under fed conditions followed by a single dose DOR tablet and a single dose ISL capsule under fasting condition followed by a DOR/ISL FDC tablet under fasting conditions.
MK-8591A Sequence 1CEXPERIMENTALParticipants will receive a single dose DOR tablet and a single dose ISL capsule under fasting conditions followed by DOR/ISL FDC tablet under fasting conditions followed by followed by a DOR/ISL FDC tablet under fed conditions.
MK-8591A Sequence 2CEXPERIMENTALParticipants will receive a single dose DOR tablet and a single dose ISL capsule under fasting conditions followed by DOR/ISL FDC tablet under fed conditions followed by followed by a DOR/ISL FDC tablet under fasting conditions.

Interventions

NameTypeDescription
MK-8591ADRUGFDC tablet of 100 mg doravirine, 0.75 mg islatravir taken orally, once daily for up to 192 weeks
IslatravirDRUGOral capsule
DoravineDRUGOral tablet
Unlock Study Design Details

Eligibility Criteria

Age Range18 Years to N/A
SexALL
Healthy VolunteersNo
Study Sites93

Inclusion Criteria: * Is currently receiving DOR 100 mg/ISL 0.75 mg adult FDC tablet in an MSD-sponsored clinical study and has completed the last treatment visit. * Is considered by the investigator to have derived clinical benefit from receiving DOR/ISL and for whom further treatment with DOR/ISL...

Countries:United StatesAustraliaCanadaChileColombiaFranceGermanyItalyJapanNew ZealandPolandRussiaSouth AfricaSpainSwitzerlandUnited Kingdom
Unlock Eligibility Criteria

Frequently asked questions about MK-8591A

What is MK-8591A used for in HIV-1 infection?

MK-8591A is an investigational small molecule being developed for the treatment of HIV-1 infection. It is a combination of doravirine and islatravir, studied as a once-daily oral regimen. The drug is currently in Phase 3 clinical development for this indication.

What does MK-8591A target?

MK-8591A combines doravirine, a non-nucleoside reverse transcriptase inhibitor, and islatravir, a nucleoside reverse transcriptase inhibitor. Both components target the HIV-1 reverse transcriptase enzyme, interfering with viral replication. The combination is designed to provide a complete antiretroviral regimen.

Who makes MK-8591A?

MK-8591A is being developed by Merck & Company, Inc., a pharmaceutical company traded on the New York Stock Exchange under the ticker symbol MRK. Merck is conducting clinical trials to evaluate the safety and efficacy of this investigational combination therapy.

What phase is MK-8591A in?

MK-8591A is in Phase 3 clinical development for HIV-1 infection. It is an investigational drug and has not been approved by regulatory authorities. A Phase 3 trial is currently active but not recruiting participants, while a Phase 1 study in healthy volunteers has been completed.

What clinical trials is MK-8591A in?

MK-8591A is being evaluated in a Phase 3 open-label follow-up study (NCT04776252) enrolling 2,000 participants with HIV-1 infection across multiple countries. A Phase 1 study (NCT06719570) in healthy adults has been completed, examining the drug's effect with food.

Is MK-8591A the same as doravirine/islatravir?

Yes, MK-8591A is the combination of doravirine and islatravir, often referred to as DOR/ISL. The Phase 3 trial title describes it as doravirine/islatravir (DOR/ISL 100 mg/0.75 mg). This combination is being studied as a single-tablet regimen for HIV-1 treatment.