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A study of islatravir and ulonivirine for adults with HIV who have not received previous treatment

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study is being conducted to investigate a new treatment approach for people living with HIV. The research focuses on testing the effectiveness and safety of two experimental drugs, islatravir and ulonivirine, which are combined in a single medication known as MK-8591B. This combination is intended to be taken once a week. The study will compare this weekly regimen against a standard daily medication containing bictegravir, emtricitabine, and tenofovir alafenamide.

The goal of the study is to evaluate how well the experimental treatment controls the HIV-1 RNA, which is a measure of the amount of virus in the blood. The research also aims to monitor the safety and how well the body tolerates the medications over time. During the course of the study, participants will be observed for a set period to track changes in their viral levels and their CD4+ T-cell count, which is a type of white blood cell that helps the body fight infections.

The study is divided into two stages. In the first stage, the effectiveness and safety of the weekly treatment are assessed in an open manner. In the second stage, a more controlled method is used where neither the participants nor the researchers know which specific treatment is being administered to ensure unbiased results. Participants will be monitored through various stages of the study to collect data on how the virus responds to the treatment and to identify any potential side effects.

The research process

The trial runs in 2 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Participation in phase 2

    The phase 2 stage of the study involves taking either a test medication or a comparator medication.

    If assigned to the test medication, the dose consists of islatravir (2 mg in a capsule) and ulonivirine (200 mg in a tablet) taken once weekly.

    If assigned to the comparator medication, the dose consists of emtricitabine, tenofovir alafenamide, and bictegravir (275 mg) taken once daily.

    This stage lasts for 24 weeks to monitor how well the medicine works to reduce the amount of hiv-1 rna (the virus in the blood) and to check for safety and tolerability (how well the body handles the medicine).

  2. Step 2

    Participation in phase 3

    The phase 3 stage continues to evaluate the effectiveness and safety of the treatments over a longer period.

    The test medication involves taking islatravir and ulonivirine combined in a single film-coated tablet (202 mg) once weekly. during this stage, some participants may receive a placebo (a pill with no active medicine) in addition to other treatments to maintain the double-blind nature of the study, meaning neither the participant nor the researchers know which specific treatment is being given.

    The comparator medication involves taking emtricitabine, tenofovir alafenamide, and bictegravir (275 mg) once daily. some participants may receive a placebo to match the test group.

    This stage lasts for 48 weeks. the effectiveness is measured by checking if the hiv-1 rna levels are below 50 copies/ml. safety is monitored by tracking any adverse events (side effects) and changes in cd4+ t-cell count (a type of immune cell that helps fight infection).

Who can join the trial?

6 criteria

  • You must be positive for HIV-1, which is a specific type of the human immunodeficiency virus.
  • For the second stage of the study, the amount of HIV-1 RNA (the genetic material of the virus) in your blood must be between 500 and 100,000 copies per milliliter.
  • For the third stage of the study, the amount of HIV-1 RNA in your blood must be 500 copies per milliliter or more.
  • For the second stage of the study, you must have a CD4+ T-cell count of at least 200 cells per cubic millimeter. CD4+ T-cells are a type of white blood cell that helps your body fight infections.
  • You must be naïve to antiretroviral therapy, which means you have never taken any antiretroviral medication (drugs used to treat HIV) after being diagnosed with the virus.
  • You must be between the ages of 3 and 12 years old.

Who cannot join the trial?

5 criteria

  • You have an infection caused by human immunodeficiency virus type 2 (HIV-2), which is a different type of virus than the more common HIV-1.
  • You have been diagnosed with an opportunistic infection, which is a serious infection that occurs more frequently or more severely in people with weakened immune systems, specifically those with AIDS (acquired immune deficiency syndrome).
  • You have an active infection of the hepatitis C virus (HCV) or the hepatitis B virus (HBV), which are viruses that cause inflammation of the liver.
  • You have had malignancy, which is another word for cancer, within the last 5 years, unless it was a specific type of skin cancer or early-stage cancer that has been properly treated.
  • You have previously taken islatravir (ISL) or ulonivirine (ULO) at any time before starting this study.
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Investigated drugs

  • Islatravir

    is an experimental medication being tested for its ability to help manage HIV by preventing the virus from replicating in the body.

  • Ulonivirine

    is an experimental medication being tested to see how well it works as a treatment to control HIV levels.

  • MK-8591B

    is a combination of two experimental medicines, islatravir and ulonivirine, being studied together to evaluate their effectiveness in treating HIV.

  • Bictegravir, emtricitabine, and tenofovir alafenamide

    is a standard daily medication used as a comparison to see how the new experimental treatments perform in controlling the HIV virus.

What is already known about the treatment

  • Emtricitabine, Tenofovir Alafenamide and Bictegravir

    This medication is taken orally as a daily pill used to treat people living with HIV. It is a well-established combination therapy currently used in standard medical practice to manage the virus. The drugs work together by blocking different stages of the HIV life cycle, such as preventing the virus from copying its genetic material and stopping it from integrating into human cells. It belongs to a class of medicines known as antiretrovirals.

  • Islatravir

    This substance is administered orally in capsule form and is currently being studied in clinical trials for the treatment of HIV. It functions as a nucleoside reverse transcriptase inhibitor, which means it works at a molecular level to stop the virus from building new strands of its genetic code. This mechanism prevents the virus from multiplying within the body.

  • Ulonivirine

    This medication is taken orally in tablet form and is currently undergoing investigation in medical research for its ability to treat HIV. It belongs to a class of drugs that target the virus's ability to replicate by interfering with essential viral processes at a molecular level. By disrupting these processes, the drug helps to reduce the amount of virus present in the body.

  • MK-8591B

    This is a combination medication taken orally as a film-coated tablet that contains both islatravir and ulonivirine. It is currently being tested in clinical studies to see how effective this specific mix is for treating HIV. The two components work together to attack the virus through different molecular pathways, making it harder for the virus to replicate.

Investigated diseases

Human Immunodeficiency Virus Type 1 - This is a virus that attacks the body's immune system, specifically the cells that help the body fight off infections. As the virus replicates, it gradually reduces the number of these important immune cells. Over time, the decreasing cell count makes the body more susceptible to various illnesses. The virus remains in the body and continues to multiply throughout the course of the infection.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IVTrial ID2025-522519-40-00Protocol codeMK-8591B-062Estimated enrolment520 patientsSponsorMerck Sharp & Dohme LLC

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