Merck to Initiate Phase 3 Trials for Investigational Once-Monthly HIV Prevention Pill

In collaboration with the Gates Foundation, Merck advances MK-8527 pre-exposure prophylaxis (PrEP) clinical trials globally

Merck (NYSE:MRK), known as MSD outside of the United States and Canada, today announced the initiation of the EXPrESSIVE Phase 3 clinical trials, evaluating the safety and efficacy of MK-8527, an investigational once-monthly, oral nucleoside reverse transcriptase translocation inhibitor (NRTTI) for HIV pre-exposure prophylaxis (PrEP). The EXPrESSIVE-11 (MK-8527-011, NCT 07044297) trial will evaluate the safety and efficacy of MK-8527 among people with greater likelihood of HIV-1 exposure in 16 countries and will begin enrolling in August 2025. In collaboration with the Gates Foundation, the EXPrESSIVE-10 (MK-8527-010) trial will evaluate the safety and efficacy of MK-8527 in women and adolescent girls in sub-Saharan Africa and will begin enrolling in the next few months.

"According to UNAIDS, 1.3 million people acquired HIV in 2023, highlighting the continued need for new PrEP options like our investigational once-monthly, oral PrEP candidate MK-8527, especially among women in sub-Saharan Africa and men who have sex with men, who experience disproportionately high rates of HIV," said Dr. Eliav Barr, senior vice president, head of global clinical development and chief medical officer, Merck Research Laboratories. "Our collaboration with the Gates Foundation will help us explore the potential of MK-8527 to contribute to global efforts to reduce the number of HIV infections and help support opportunities to accelerate access around the world."

The decision to initiate the Phase 3 clinical trial program was supported by the results of a double-blind, multicenter, Phase 2 trial (MK-8527-007, NCT 06045507) examining the safety and pharmacokinetics of MK-8527. The study enrolled 350 participants, 18–65 years of age, with low likelihood of HIV-1 exposure, who were randomized 2:2:2:1 to receive MK-8527 (3, 6, or 12 mg) or placebo once monthly for six months. In the trial, the rates of adverse events were similar among those in the MK-8527 arms and those in the placebo arm, and no clinically meaningful changes were seen in laboratory tests, including total lymphocyte and CD4 T-cell counts. The pharmacokinetics of MK-8527 and MK-8527-TP, the active form of MK-8527, support the continued development of MK-8527 as an oral, once-monthly option for PrEP. Results from the Phase 2 trial were highlighted in the opening press conference for IAS 2025, the 13th International AIDS Society Conference on HIV Science in Kigali, Rwanda, on Monday, July 14, at 15:30 – 16:30 CAT, titled "Breakthroughs Amid Crisis: The Future of HIV Innovation." These research findings will be further detailed in a late-breaker oral session on Wednesday, July 16, at 12:15 – 13:15 CAT.

"Scientific advances against HIV have brought us further than ever imagined and are ushering in a new era in HIV prevention," said Trevor Mundel, president of global health at the Gates Foundation. "With only 18% of global PrEP need currently met, there is a clear and urgent need for options like MK-8527 that may offer the ability to prevent infection. These Phase 3 trials are a key step toward translating progress into longer-acting options that could help turn the tide on HIV."

In the EXPrESSIVE-10 trial, the International Clinical Research Center (ICRC) within the University of Washington Department of Global Health, in partnership with the University of Alabama at Birmingham, will receive grant funding from the Gates Foundation to support ICRC's collaboration with 31 clinical research trial sites in Kenya, South Africa, and Uganda; sites will inform and engage communities and recruit, enroll, and follow women who participate in the EXPrESSIVE-10 trial. Merck will be the trial sponsor, gaining regulatory and customs approvals, and providing operational expertise and resources for management of the trials. The Gates Foundation will also provide support for global community advisory groups, which will offer insight into community perspectives on a monthly PrEP pill, participant recruitment materials and strategies, and cultural considerations for these trials. Separately, the Gates Foundation will provide grant funding for EXPrESSIVE-11 to support the establishment of a community advisory group and the development of recruiting and retention materials only.

About the EXPrESSIVE MK-8527 Phase 3 Clinical Trial Program

The EXPrESSIVE-11 trial (MK-8527-011, NCT 07044297) is a randomized, active-controlled study enrolling 4,390 sexually active people who could benefit from PrEP across trial sites in 16 countries. The primary objective of the study is to evaluate the efficacy, safety, and tolerability of once-monthly oral MK-8527 compared to daily emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) as assessed by the incidence rate per year of adjudicated HIV-1 infections. The trial will begin enrolling in August 2025.

The EXPrESSIVE-10 trial (MK-8527-010) is a randomized, active-controlled study enrolling 4,580 sexually active women aged 16 to 30 in Kenya, South Africa, and Uganda. The primary objective of the study is to evaluate the efficacy, safety, and tolerability of once-monthly oral MK-8527 compared to daily emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) as assessed by the incidence rate per year of adjudicated HIV-1 infections. The study will begin enrolling in the next few months.

About MK-8527

MK-8527 is being evaluated as a potential once-monthly oral prevention option for HIV-1. MK-8527 inhibits reverse transcriptase through multiple mechanisms of action, including inhibition of translocation and delayed chain termination. For an overview of Merck's complete HIV treatment and prevention clinical development program, please click here.

Merck's Commitment to HIV

For more than 35 years, Merck has been committed to scientific research and discovery in HIV, leading to scientific breakthroughs that have helped change HIV treatment. Our work has helped pioneer the development of new options across multiple drug classes to help those impacted by HIV. Today, we are developing a series of antiviral options designed to help people manage their HIV and to help prevent HIV, with the goal of reducing the growing burden of HIV worldwide. We want to ensure people are not defined by HIV, and our work focuses on transformational innovations, collaborations with others in the global HIV community, and access initiatives aimed at helping to end the HIV epidemic for everyone.

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable, and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube, and LinkedIn.

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