Once-Weekly Islatravir/Lenacapavir Meets Primary Endpoints in Two Phase 3 Trials

Gilead and Merck announce positive Phase 3 results for Islatravir/Lenacapavir and prepare to file for approval worldwide.

Gilead Sciences and Merck (known as MSD outside the United States and Canada) have announced Phase 3 results for their once-weekly oral HIV antiretroviral regimen, "Islatravir/Lenacapavir (ISL/LEN)," which successfully met the primary endpoint in both of its pivotal trials: ISLEND-1 and ISLEND-2.

These results mark an important milestone in the development of a new generation of HIV medications aimed at reducing the burden of daily dosing. They offer people living with HIV whose virus is already suppressed a more convenient treatment option, requiring only one dose per week. If approved by regulators, this could become the first once-weekly oral single-tablet HIV antiretroviral therapy.

What Did the Phase 3 Studies Show?

Both studies were designed to evaluate the efficacy and safety of Islatravir 2 mg combined with Lenacapavir 300 mg in people living with HIV whose virus was already suppressed.

The ISLEND-1 Study

This study compared people who switched from BIKTARVY, one of the most widely used HIV treatment regimens, to the once-weekly ISL/LEN regimen. The results showed:

• ISL/LEN was non-inferior to BIKTARVY.
• It effectively maintained viral suppression.
• Safety was comparable to the BIKTARVY group.
• No new safety signals of concern were identified.

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The ISLEND-2 Study

This study compared patients who switched from a range of standard daily HIV treatment regimens to once-weekly ISL/LEN. The results showed:

• ISL/LEN was non-inferior to standard treatment.
• It maintained viral suppression well.
• Its safety profile was comparable to patients' previous regimens.
• No new safety issues were identified.

Why Is the Islatravir/Lenacapavir Regimen So Promising?

Today, most people living with HIV still need to take antiretroviral medication every day, even though long-acting injectable options are already available. The ISL/LEN regimen has drawn considerable interest because it combines two drugs with different mechanisms of action, both of which are long-acting.

Islatravir

Islatravir is a next-generation nucleoside analog developed by Merck. Its key strength is the ability to inhibit HIV replication through several mechanisms:

• Blocking the action of the reverse transcriptase enzyme.
• Halting the formation of the virus's DNA strand.
• Disrupting the structure of the virus's DNA at a later stage.

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Lenacapavir

Lenacapavir, developed by Gilead, is the world's first capsid inhibitor. Unlike earlier generations of HIV drugs, it can block multiple stages of the virus's life cycle, such as:

• Interfering with the viral capsid to block delivery of the virus's genetic material into the cell nucleus.
• Viral assembly.
• Viral spread.

In addition, laboratory data have shown no cross-resistance with the HIV antiretroviral drugs currently in use.

Expert Commentary

Dr. Jared Baeten, Senior Vice President of Clinical Development at Gilead, said that long-acting oral treatment is an emerging wave of HIV innovation with the potential to transform care in the future. Less frequent dosing may offer greater flexibility and privacy for people living with HIV.

Dr. Eliav Barr, Head of Global Clinical Development at Merck, noted that these results reflect both companies' shared commitment to developing new options for people living with HIV. If approved, this regimen would be the first long-acting oral option taken just once a week.

What Comes Next

Gilead and Merck have said they are preparing to submit data from both Phase 3 studies to drug regulators in many countries around the world. The complete results of ISLEND-1 and ISLEND-2 will also be presented at upcoming HIV scientific conferences. If approved, the Islatravir/Lenacapavir regimen could become another major turning point in HIV treatment by reducing dosing frequency, making everyday life more convenient, and expanding treatment options for people living with HIV around the world.

Although advances in antiretroviral drugs have helped people living with HIV enjoy a good quality of life and a lifespan close to that of the general population, there is currently no broadly available cure for HIV, but effective ART can prevent progression to AIDS. Taking antiretroviral medication consistently, monitoring your health regularly, and accessing prevention services such as PrEP and PEP remain central to ending the HIV epidemic worldwide.

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Source: Gilead Sciences & Merck. (2026). "Gilead and Merck Announce Positive Topline Results From Two Phase 3 Studies Evaluating Islatravir/Lenacapavir, an Oral Once-Weekly HIV Treatment" https://www.gilead.com/news/news-details/2026/gilead-and-merck-announce-positive-topline-results-from-two-phase-3-studies-evaluating-islatravirlenacapavir-an-oral-once-weekly-hiv-treatment

Verified references

Links and relevance to the article’s main topic were reviewed on 13 August 2026. Each source supports only the scope stated in the original document and does not replace personalised medical, legal, or service advice.

1. Merck/Gilead: Phase 3 once-weekly islatravir/lenacapavir results Accessed 13 August 2026
2. NIH HIVinfo: HIV Treatment Basics Accessed 13 August 2026
3. NIH HIVinfo: HIV Medicines and Side Effects Accessed 13 August 2026