Merck Presents HIV Prevention and Treatment Portfolio at IAS 2025 with Focus on Once-Monthly PrEP

At the 13th International AIDS Society Conference on HIV Science (IAS 2025), Merck presented new data that underscores the company’s growing pipeline of HIV prevention and treatment options, including promising once-daily, once-weekly, and once-monthly oral regimens. Among the most closely watched programs is MK-8527, an investigational once-monthly oral PrEP candidate, which Merck scientists say could be a game-changer in HIV prevention.

In the second part of our interview ahead of the conference, Luisa M Stamm, MD, PhD, associate vice president of infectious disease clinical research and section head for HIV at Merck, emphasized the potential impact of MK-8527. “Firstly, with regard to 8527, it has the potential to be really transformative for the field,” Stamm said. “With monthly oral dosing, we think it could really address the issues and the challenges that we've had to date in terms of prevention — both the adherence, the pill burden, and implementation and persistence. So we think it's a really special program that really fits into the armamentarium to address the global needs for people who could most benefit from PrEP.”

Phase 2 data on MK-8527, presented in a late-breaking oral session at IAS 2025, focused on safety and pharmacokinetics in adults at low risk for HIV-1 exposure. According to the company, the once-monthly oral formulation could offer a convenient and effective alternative to daily PrEP, especially for populations where adherence remains a challenge.

Stamm also pointed to Merck’s broader HIV portfolio, noting that “we have not only a monthly oral PrEP option in development, but we also have daily and weekly treatment options that are in development — all of which are anchored on the same NRTTI mechanism that we just discussed for 8527.”

That shared mechanism is islatravir, the backbone of several of Merck’s investigational regimens. For example, the doravirine/islatravir (DOR/ISL) combination was featured in phase 3 data presented at IAS, with a specific focus on patients with pre-existing resistance-associated mutations, such as M184V. Stamm said the results remained strong even among this more challenging patient population.

“We had positive phase 3 results at CROI earlier this year and at IAS. The resistance profile that we observed in the phase 3 studies — the bottom line is that about a quarter of individuals in the virologically suppressed program had baseline resistance-associated mutations, including M184V. And overall, the efficacy was maintained, with over 93% of individuals maintaining virologic suppression,” she explained.

Another major component of Merck’s HIV pipeline is the once-weekly oral regimen combining islatravir and ulonivirine (ISL/ULO). At IAS 2025, Merck presented new results from two phase 1 trials and a phase 2b dose-ranging study, including data on a previous program using a higher 20 mg dose of islatravir. While that program was paused, the learnings are being applied to a new phase 2 regimen using optimized doses of islatravir (2 mg) and ulonivirine (200 mg).

“We’ll be presenting the results from a phase 2 study that was previously conducted with a higher dose of islatravir. Although that program was put on hold, there are some important learnings here that we're applying to our current phase 2 program — with respect to the efficacy that was observed, as well as the overall AE profile, which was comparable to Biktarvy in that virologically suppressed study,” Stamm said.

Merck also presented phase 1 data on ulonivirine, including long-term dosing results and a drug-drug interaction (DDI) study with islatravir. These findings supported the relaunch of the weekly treatment program, which is now ongoing.

“These phase 1 studies are also important in supporting us restarting the phase 2 program of islatravir. We have long-term dosing with ulonivirine, in which we saw no safety concerns. And then we have a DDI study with islatravir and ulonivirine,” Stamm said. “So, all of that data together is supportive of restarting the weekly dosing of islatravir at 2 milligrams and ulonivirine at 200 milligrams. That virologically suppressed phase 2 study is ongoing right now.”

Reference

Merck & Co., Inc. Merck to Present New Data Highlighting Research Advancements Across its HIV Prevention and Treatment Pipeline at IAS 2025. Business Wire. Published July 8, 2025. Accessed July 18, 2025. https://www.merck.com/news/merck-to-present-new-data-highlighting-research-advancements-across-its-hiv-prevention-and-treatment-pipeline-at-ias-2025/