RAHWAY, N.J. – October 15, 2025 — Merck (NYSE: MRK) announced new Phase 3 trial results for its investigational, once-daily, two-drug oral regimen doravirine/islatravir (DOR/ISL) in virologically suppressed adults with HIV-1 infection. Presented at the 20th European AIDS Conference in Paris, the findings demonstrated minimal changes in weight and body composition, with no clinically meaningful impact on fasting lipids or insulin resistance, confirming the regimen’s non-inferiority to current three-drug therapies such as BIC/FTC/TAF.
Science Significance
The Phase 3 MK-8591A-052 and MK-8591A-051 trials underscore the scientific advancement of DOR/ISL as a simplified antiretroviral regimen maintaining viral suppression while reducing drug exposure. The studies reported no treatment-emergent resistance, supporting the molecule’s long-term durability and tolerability profile. The findings also reinforce Merck’s NRTTI-based innovation (nucleoside reverse transcriptase translocation inhibitor), which may redefine HIV treatment protocols.
Regulatory Significance
The U.S. Food and Drug Administration (FDA) has accepted the New Drug Application (NDA) for DOR/ISL, setting a target action date of April 28, 2026, under the Prescription Drug User Fee Act (PDUFA). This marks a crucial regulatory step toward making a dual-drug oral therapy available for virologically suppressed HIV-1 adults, supporting Merck’s ongoing dialogue with global health authorities for broader market approvals.
Business Significance
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From a business standpoint, the success of DOR/ISL bolsters Merck’s HIV franchise and aligns with its strategic pipeline diversification. Positive Phase 3 data enhances investor confidence, especially following prior efficacy reports at CROI 2025. With Merck’s established antiviral portfolio, including PIFELTRO® and DELSTRIGO®, DOR/ISL could strengthen its competitive edge in the multi-billion-dollar antiretroviral market.
Patients’ Significance
For people living with HIV, maintaining long-term viral suppression while minimizing metabolic and weight-related effects is crucial. The DOR/ISL regimen offers a simplified, tolerable, and effective treatment alternative, addressing adherence challenges and reducing long-term toxicity risks. These benefits represent a significant step forward in personalized HIV management.
Policy Significance
The study’s outcomes support global HIV policy initiatives, particularly those promoting treatment simplification and access in resource-limited regions. If approved, DOR/ISL could influence future WHO and CDC HIV guidelines, aligning with international goals to end the HIV epidemic through innovation and accessibility.
Transaction Highlights
With over 35 years of dedication to HIV research, Merck continues to lead advancements in antiviral therapies aimed at improving quality of life and reducing disease burden. The Phase 3 success of DOR/ISL underscores the company’s commitment to innovation, collaboration, and patient-centered care. Pending FDA approval, DOR/ISL could become a cornerstone of next-generation HIV treatment, reshaping clinical practice worldwide.
Source: Merck & Co., Inc.. Press Release
