Merck to initiate Phase 3 trials for investigational once-monthly HIV prevention pill
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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

  • By IPP Bureau | July 14, 2025

Merck 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 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 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 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.

“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.”

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