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DOR/ISL

Phase 3

HIV Infection | Small molecule | Infectious Disease |Merck & Company, Inc.|Last Updated: Jun 3, 2026

Success Probability

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Market & Valuation

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Trial Design

RandomizedDouble-BlindACTIVE_CONTROLLEDDMC
Total Trials3
Total Enrollment1,956

FDA Designations

No designations recorded

Clinical trial landscape

DOR/ISL · 8 trials · 3 indications

Phase 3 6Phase 2 1Phase 1 1
NCT05766501A Study of Doravirine/Islatravir (DOR/ISL, MK-8591A) for the Treatment of Human Immunodeficiency Virus 1 (HIV-1) Infection in Participants Who Previously Received DOR/ISL (MK-8591A-054)HIV Infection
ACTIVE NOT_RECRUITING641 Analytics
NCT05705349DOR/ISL in HIV-1 Antiretroviral Treatment-naïve Participants (MK-8591A-053)HIV-1 Infection
ACTIVE NOT_RECRUITING537 Analytics
NCT05630755A Switch to Doravirine/Islatravir (DOR/ISL) in Participants With Human Immunodeficiency Virus Type 1 (HIV-1) Who Are Virologically Suppressed on Bictegravir/Emtricitabine/Tenofovir Alafenamide (BIC/FTC/TAF) (MK-8591A-052)HIV-1 Infection
ACTIVE NOT_RECRUITING514 Analytics
NCT04233879Study of Doravirine/Islatravir (DOR/ISL 100 mg/0.75 mg) to Evaluate the Antiretroviral Activity, Safety, and Tolerability in Treatment-Naïve Participants With Human Immunodeficiency Virus Type 1 (HIV-1) Infection (MK-8591A-020)HIV-1 Infection
COMPLETED599 Analytics
NCT04223778Safety and Efficacy of a Switch to Doravirine/Islatravir in Participants With HIV-1 (MK-8591A-017)HIV Infection
COMPLETED672 Analytics
NCT04223791Switch to Doravirine/Islatravir (DOR/ISL) in Human Immunodeficiency Virus 1 (HIV-1) Participants Treated With Bictegravir/Emtricitabine/Tenofovir Alafenamide (BIC/FTC/TAF) (MK-8591A-018)HIV Infection
COMPLETED643 Analytics
PHASE3ACTIVE NOT_RECRUITING
A Study of Doravirine/Islatravir (DOR/ISL, MK-8591A) for the Treatment of Human Immunodeficiency Virus 1 (HIV-1) Infection in Participants Who Previously Received DOR/ISL (MK-8591A-054)
HIV InfectionUnlock trial analytics
PHASE3ACTIVE NOT_RECRUITING
DOR/ISL in HIV-1 Antiretroviral Treatment-naïve Participants (MK-8591A-053)
HIV-1 InfectionUnlock trial analytics
PHASE3ACTIVE NOT_RECRUITING
A Switch to Doravirine/Islatravir (DOR/ISL) in Participants With Human Immunodeficiency Virus Type 1 (HIV-1) Who Are Virologically Suppressed on Bictegravir/Emtricitabine/Tenofovir Alafenamide (BIC/FTC/TAF) (MK-8591A-052)
HIV-1 InfectionUnlock trial analytics
PHASE3COMPLETED
Study of Doravirine/Islatravir (DOR/ISL 100 mg/0.75 mg) to Evaluate the Antiretroviral Activity, Safety, and Tolerability in Treatment-Naïve Participants With Human Immunodeficiency Virus Type 1 (HIV-1) Infection (MK-8591A-020)
HIV-1 InfectionUnlock trial analytics
PHASE3COMPLETED
Safety and Efficacy of a Switch to Doravirine/Islatravir in Participants With HIV-1 (MK-8591A-017)
HIV InfectionUnlock trial analytics
PHASE3COMPLETED
Switch to Doravirine/Islatravir (DOR/ISL) in Human Immunodeficiency Virus 1 (HIV-1) Participants Treated With Bictegravir/Emtricitabine/Tenofovir Alafenamide (BIC/FTC/TAF) (MK-8591A-018)
HIV InfectionUnlock trial analytics

Study Endpoints

Primary Endpoints

Percentage of Participants with One or More Adverse Event (AE)
Up to 96 Weeks

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. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a study intervention. The percentage of participants who experience an AE through Week 96 will be presented.

Percentage of participants who Discontinue Study Intervention Due to an AE
Up to 96 Weeks

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. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a study intervention. The percentage of participants who discontinue study intervention due to an AE through Week 96 will be presented.

Percentage of participants with human immunodeficiency virus type 1 (HIV-1) ribonucleic acid (RNA) <50 copies/mL at Week 48
Week 48

Plasma HIV-1 RNA quantification will be performed at the central laboratory using a polymerase chain reaction (PCR) assay with a lower limit of detection of \<50 copies/mL.

Percentage of participants experiencing ≥1 adverse event (AE) through Week 48
Up to 48 weeks

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.

Percentage of participants discontinuing from study treatment due to an AE through Week 48
Up to 48 weeks

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.

Percentage of Participants With Human Immunodeficiency Virus Type 1 (HIV-1) Ribonucleic Acid (RNA) ≥50 Copies/mL at Week 48
Week 48

HIV-1 RNA levels in blood samples taken at each visit were measured with a reliable lower limit of quantification of \<50 copies/mL. The percentage of participants with HIV-1 RNA ≥50 copies/mL at Week 48 is presented using the FDA Snapshot missing data approach.

Percentage of Participants Who Experience Adverse Events (AEs) Through Week 48
Up to Week 48

An AE was defined as 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 percentage of participants who experienced at least one AE is reported.

Percentage of Participants Who Discontinue Study Intervention Due to AEs Through Week 48
Up to Week 48

An AE was defined as 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 percentage of participants who discontinued study intervention due to an AE is reported.

Percentage of Participants With Human Immunodeficiency Virus (HIV)-1 Ribonucleic Acid (RNA) <50 Copies/mL at Week 48
Week 48

The Abbott RealTime polymerase chain reaction (PCR) assay with a reliable lower limit of quantification of 40 copies/mL was used to measure the HIV-1 RNA level in blood samples obtained at each visit. The percentage of participants with HIV-1 RNA \<50 copies/mL at Week 48 was presented using the Food and Drug Administration (FDA) Snapshot missing data approach. The final analysis for this outcome is presented here.

Percentage of Participants Who Experienced an Adverse Event (AE) up to Week 48
Up to approximately 48 weeks

An AE was any untoward medical occurrence in a study participant administered a study drug, which does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of the study drug whether or not it is considered related to the study drug. The percentage of participants who experienced at least one AE up to Week 48 was reported. The final analysis for this outcome is presented here.

Percentage of Participants Who Discontinued Study Treatment Due to an AE up to Week 48
Up to approximately 48 weeks

An AE was any untoward medical occurrence in a study participant administered a study drug, which does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of the study drug whether or not it is considered related to the study drug. The percentage of participants who discontinued study treatment due to an AE up to Week 48 were reported. The final analysis for this outcome is presented here.

Percentage of Participants With Human Immunodeficiency Virus (HIV)-1 Ribonucleic Acid (RNA) ≥50 Copies/mL at Week 48
Week 48

HIV-1 RNA levels in blood samples taken at each visit were measured by the Abbott RealTime polymerase chain reaction (PCR) assay with a reliable lower limit of quantification of 40 copies/mL. The percentage of participants with HIV-1 RNA ≥50 copies/mL at Week 48 is presented using the FDA Snapshot missing data approach.

Percentage of Participants With One or More Adverse Events (AEs) up to Week 48
Up to ~48 Weeks

An AE was defined as 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 percentage of participants who experienced at least one AE was reported.

Percentage of Participants Who Discontinued Study Intervention Due to an AE up to Week 48
Up to ~48 Weeks

An AE was defined as 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 percentage of participants who discontinued study intervention due to an AE was reported.

Percentage of Participants With Human Immunodeficiency Virus 1 Ribonucleic Acid (HIV-1 RNA) ≥50 Copies/mL at Week 48
Week 48

The Abbott RealTime polymerase chain reaction (PCR) assay with a reliable lower limit of quantification of 40 copies/mL was used to measure the HIV-1 RNA level in blood samples obtained at each visit. Per protocol, the primary outcome measure, the percentage of participants with HIV-1 RNA ≥50 copies/mL at Week 48, is presented using the Food and Drug Administration (FDA) Snapshot missing data approach. The percentage values were rounded to the nearest tenth digit.

Area Under the Plasma Drug Concentration-time Curve From 0 to 24 Hours Post-dose (AUC0-24) of Islatravir (ISL)
Pre-dose, and 0.5, 1, 2, 4, 8, 12, and 24 hours post-dose on Day 28

The AUC0-24 of ISL in plasma was determined at steady state.

Maximum Plasma Concentration (Cmax) of ISL
Pre-dose, and 0.5, 1, 2, 4, 8, 12, and 24 hours post-dose on Day 28

The Cmax of ISL in plasma was determined at steady state.

Time to Reach Maximum Plasma Concentration (Tmax) of ISL
Pre-dose, and 0.5, 1, 2, 4, 8, 12, and 24 hours post-dose on Day 28

The Tmax of ISL in plasma was determined at steady state.

Apparent Plasma Terminal Half-life (t½) of ISL
Pre-dose, and 0.5, 1, 2, 4, 8, 12, and 24 hours post-dose on Day 28

The t½ of ISL in plasma was determined at steady state.

Apparent Total Clearance From Plasma (CL/F) of ISL
Pre-dose, and 0.5, 1, 2, 4, 8, 12, and 24 hours post-dose on Day 28

The CL/F of ISL from plasma was determined at steady state.

Apparent Volume of Distribution During Terminal Phase (Vz/F) of ISL
Pre-dose, and 0.5, 1, 2, 4, 8, 12, and 24 hours post-dose on Day 28

The Vz/F of ISL was determined at steady state.

AUC0-last of ISL-triphosphate (ISL-TP) in Peripheral Blood Mononuclear Cells (PBMCs)
Pre-dose, and 4 and 24 hours post-dose on Day 28

The AUC0-24 of ISL-TP in PBMCs was determined at steady state.

Cmax of ISL-TP in PBMCs
Pre-dose, and 4, and 24 hours post-dose on Day 28

The Cmax of ISL-TP in PBMCs was determined at steady state.

C24 of ISL-TP in PBMCs
24 hours post-dose on Day 28

The C24 of ISL-TP in PBMCs was determined at steady state.

Number of Participants Experiencing ≥1 Adverse Event (AE)
Up to 24 weeks

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.

Number of Participants Discontinuing From Study Treatment Due to an AE
Up to 24 weeks

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.

Cumulative Amount of DOR Excreted in Breast Milk From 0 to 24 Hours (Ae0-24hrs)
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
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
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)
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
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
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.

Secondary Endpoints

Percentage of Participants with HIV-1 Ribonucleic Acid (RNA) ≥50 copies/mL at Week 96
Week 96
Percentage of Participants with HIV-1 RNA <50 copies/mL at Week 96
Week 96
Percentage of Participants with HIV-1 RNA <200 copies/mL at Week 96
Week 96
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Study Design & Arms

AllocationNA
MaskingNONE
ModelSINGLE_GROUP
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
DOR/ISLEXPERIMENTALParticipants will receive fixed dose combination (FDC) tablet of DOR/ISL (100 mg/0.25 mg) taken once daily (QD) orally from Day 1 to Week 96. After Week 96, eligible participants may continue on DOR/ISL until week 240 or until DOR/ISL becomes commercially accessible, whichever comes first.
BIC/FTC/TAFACTIVE_COMPARATORParticipants take BIC/FTC/TAF and placebo to DOR/ISL qd for 144 weeks.
DOR/ISL and Placebo to BIC/FTC/TAFEXPERIMENTALParticipants will receive DOR/ISL 100 mg/0.25 mg and Placebo to BIC/FTC/TAF once daily (QD) orally from day 1 to week 144. After week 144, eligible participants may continue on DOR/ISL and continue study treatment until week 240 or to when DOR/ISL becomes commercially accessible (whichever comes first).
BIC/FTC/TAF and Placebo to DOR/ISLACTIVE_COMPARATORParticipants will receive BIC/FTC/TAF 50 mg/200 mg/25 mg and Placebo to DOR/ISL once daily (QD) orally from day 1 to week 144. After week 144, eligible participants may switch to DOR/ISL and continue study treatment until week 240 or to when DOR/ISL becomes commercially accessible (whichever comes first).
Group 1: doravirine/islatravir (DOR/ISL)EXPERIMENTALTreatment-naïve participants living with human immunodeficiency virus-1 (HIV-1) that had not received ≤10 days of prior antiretroviral therapy received blinded fixed dose combination (FDC) Doravirine/Islatravir (DOR/ISL) (100 mg doravirine \[DOR\]/0.75 mg islatravir \[ISL\]) and placebo to Bictegravir/Tenofovir Alafenamide/Emtricitabine (BIC/FTC/TAF) once daily (QD) from Day 1 to Week 96, and open-label DOR/ISL up to Week 144. At Week 144, participants who consent to enter the optional open-label study extension continued to receive open-label QD FDC of DOR/ISL (100 mg/0.75 mg) for an additional 24 weeks, up to Week 168.
Group 2: bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF)ACTIVE_COMPARATORTreatment-naïve participants living with HIV-1 that had not received ≤10 days of prior antiretroviral therapy received blinded BIC/FTC/TAF (50 mg bictegravir \[BIC\], 200 mg emtricitabine \[FTC\], 25 mg tenofovir alafenamide \[TAF\]) and placebo to FDC DOR/ISL QD from Day 1 to Week 96, and open-label BIC/FTC/TAF up to Week 144. At Week 144, participants who consent to enter the optional open-label study extension continued to receive QD BIC/FTC/TAF (50 mg/200 mg/25 mg) for an additional 24 weeks, up to Week 168.
Group 2: Baseline Antiretroviral Therapy (ART)ACTIVE_COMPARATORParticipants received continuous baseline ART for 48 weeks. Continuing participants delayed switch over from baseline ART to DOR/ISL, fixed dose combination of 100 mg DOR/0.75 mg ISL orally once daily, from Week 48 to Week 96, a total DOR/ISL treatment duration of 48 Weeks.

Interventions

NameTypeDescription
DOR/ISLDRUGFDC tablet of 100 mg doravirine (DOR)/0.25 mg islatravir (ISL) taken once daily
BIC/FTC/TAFDRUGFixed dose combination tablet containing BIC/FTC/TAF 50 mg/200 mg/25 mg taken by mouth.
Placebo to DOR/ISLDRUGPlacebo tablet matched to DOR/ISL tablet taken by mouth.
Placebo to BIC/FTC/TAFDRUGPlacebo tablet matched to BIC/FTC/TAF tablet taken by mouth.
ARTDRUGBaseline ART regimen will be administered as per approved label. ART medication will not be provided by the Sponsor; participants will provide their own ART medications. Allowed drug classes include nucleoside analog reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), integrase strand transferase inhibitors (InSTIs), fusion inhibitors, chemokine receptor 5 (CCR5) antagonists, post-attachment inhibitor, and pharmacokinetic (PK) boosters.
Placebo to FDC DOR/ISLDRUGPlacebo to FDC DOR/ISL in a single tablet taken orally, once daily
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Eligibility Criteria

Age Range18 Years to N/A
SexALL
Healthy VolunteersNo
Study Sites95

Inclusion Criteria: * Is currently receiving doravirine/islatravir (DOR/ISL) adult fixed dose combination (FDC) tablet in Merck Sharp \& Dohme (MSD)-sponsored clinical studies (MK-8591A-018, -020, and -033 \[except for heavily treatment-experienced (HTE) participants\]). Exclusion Criteria: * Has...

Countries:United StatesArgentinaAustraliaCanadaChileColombiaIsraelJapanNew ZealandPuerto RicoRussiaSouth AfricaSwitzerlandTaiwanUnited KingdomDominican RepublicFranceGermanyGuatemalaKenyaMalaysiaMexicoSpainThailandTurkey (Türkiye)ItalyPolandAustriaFinland
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Recent Changes (Last 90 Days)

MEDIUMJul 4, 2026NCT04233879TRIAL_REMOVED: changed
MEDIUMJul 4, 2026NCT04233879TRIAL_REMOVED: changed
MEDIUMJul 4, 2026NCT04233879TRIAL_REMOVED: changed

Frequently asked questions about DOR/ISL

What is DOR/ISL used for?

DOR/ISL is an investigational small molecule being developed for the treatment of HIV infection and HIV-1 infection. It is being studied in adults who are virologically suppressed on other antiretroviral regimens, as well as in healthy volunteers for certain trials. The drug is currently in Phase 3 clinical development.

What does DOR/ISL target?

DOR/ISL is a combination of doravirine and islatravir. Doravirine is a non-nucleoside reverse transcriptase inhibitor, while islatravir is a nucleoside reverse transcriptase inhibitor. Both target the HIV reverse transcriptase enzyme, which is essential for viral replication.

Who makes DOR/ISL?

DOR/ISL is being developed by Merck & Company, Inc., which trades under the ticker symbol MRK. The company is conducting Phase 3 clinical trials to evaluate the safety and efficacy of this combination therapy in people living with HIV.

What phase is DOR/ISL in?

DOR/ISL is currently in Phase 3 clinical development. It is an investigational drug and has not been approved by regulatory authorities. Multiple Phase 3 trials are ongoing or have been completed to assess its safety and efficacy in treating HIV-1 infection.

What clinical trials is DOR/ISL in?

DOR/ISL is being studied in several Phase 3 trials, including NCT04223778, NCT04223791, NCT05630755, and NCT05766501. These trials evaluate switching to DOR/ISL in virologically suppressed HIV patients, with some completed and others active but not recruiting. Total enrollment across these studies is approximately 1,956 participants.

Is DOR/ISL the same as DOR/3TC/TDF?

Yes, DOR/ISL is also known as DOR/3TC/TDF. This alternative name reflects the combination of doravirine, lamivudine, and tenofovir disoproxil fumarate, which are the components of the drug. The primary name DOR/ISL emphasizes doravirine and islatravir.