MSD is advancing its once-monthly oral pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) to Phase III trials.
Announced at the International AIDS Society (IAS) 2025 conference taking place from 13-17 July in Kigali, Rwanda, MSD has launched two Phase III trials, EXPrESSIVE-10 and EXPrESSIVE-11, which will evaluate the safety and efficacy of MK-8527.
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The EXPrESSIVE-11 (NCT07044297) trial will enrol 4,390 sexually active people who could benefit from PrEP while the EXPrESSIVE-10 (MK-8527-010) trial will enrol women and adolescent girls in sub-Saharan Africa.
Both studies will compare MK-8527 against daily emtricitabine/tenofovir disoproxil fumarate (FTC/TDF), with a primary endpoint of incidence rate per year of adjudicated HIV-1 infections.
The EXPrESSIVE-10 trial is being run by the International Clinical Research Center (ICRC) within the University of Washington Department of Global Health, in partnership with the University of Alabama at Birmingham. The study 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.
The Gates Foundation will also provide financing for the EXPrESSIVE-11 study and support for global community advisory groups, which will offer insight into community perspectives on a monthly PrEP pill.
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By GlobalDataMSD Research Laboratories’ global clinical development head Dr Eliav Barr said: “According to UNAIDS, 1.3 million people acquired HIV in 2023, highlighting the continued need for new PrEP options such as 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.
“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 initiation of the Phase III clinical trial programme follows published data from a double-blind, multi-centre, Phase II trial (NCT06045507) investigating three doses of MK-8527 versus placebo. The study enrolled 350 participants, 18–65 years of age, with a low likelihood of HIV-1 exposure.
In the trial, the rates of adverse events (AEs) 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 Phase II data was also presented at IAS 2025 on 14 July.
MK-8527 is an investigational once-monthly, oral nucleoside reverse transcriptase translocation inhibitor (NRTTI).
Long-acting PrEP landscape accelerating
In addition to MSD, Gilead is also making strides in the long-acting HIV PrEP market. Just last month, Gilead received approval from the US Food and Drug Administration for its twice-yearly injectable therapy, Yeztugo (lenacapavir).
On 14 July, the World Health Organization (WHO) recommended the use of Yeztugo, with WHO’s Director-General describing the drug as the “next best thing” in the absence of a vaccine.
Gilead ran two Phase III trials, with one showing a 100% prevention of HIV and a second showing a 96% prevention.
Gilead is now trying to go one step further again and is currently trialling a once-yearly version of the therapy. Following the successful Phase I trial readout, the company is advancing the candidate to Phase III trials.
