New long-term data offer encouraging news for individuals living with HIV. A recent analysis of the Phase 3 MK-8591A-051 study demonstrates that switching to a fixed-dose combination of doravirine and islatravir (DOR/ISL, 100/0.25 mg) continues to support durable viral suppression and long-term tolerability in adults who had previously achieved viral suppression with other antiretroviral therapies. The findings, spanning 96 weeks, reinforce the potential of DOR/ISL as a viable option for maintaining HIV control.
The study, initially designed to assess the efficacy of DOR/ISL compared to a three-drug regimen, has now provided extended follow-up data confirming the sustained benefits of switching to the two-drug combination. This is particularly significant as researchers continue to explore strategies to simplify HIV treatment regimens, reducing the pill burden and potential long-term side effects for patients. Maintaining viral suppression is crucial not only for individual health but similarly for preventing transmission of the virus.
The MK-8591A-051 trial involved adults with HIV who were already virally suppressed on oral antiretroviral therapy. Participants switched to DOR/ISL, and their viral load and overall health were monitored over the 96-week period. The results indicate that the majority of participants maintained viral suppression, suggesting that DOR/ISL is an effective alternative to continuing their existing treatment. The data presented further support the growing body of evidence suggesting that a two-drug regimen can be a successful approach for certain individuals with HIV.
Durable Viral Suppression Observed
The 96-week results build upon earlier findings from the study, initially presented at the Conference on Retroviruses and Infectious Diseases (CROI) in 2025. These earlier results demonstrated non-inferiority to the three-drug regimen bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF) in maintaining viral suppression. The extended follow-up now confirms the durability of this effect. According to Merck, the data reveal minimal changes in weight and body composition, and no clinically meaningful impact on fasting lipids or insulin resistance among trial participants.
Understanding DOR/ISL
Doravirine and islatravir are both antiretroviral medications that operate by interfering with different stages of the HIV life cycle. Doravirine is a non-nucleoside reverse transcriptase inhibitor (NNRTI), while islatravir is a novel nucleoside reverse transcriptase translocation inhibitor (NRTTI). The combination of these two drugs offers a unique mechanism of action, potentially reducing the risk of drug resistance. Islatravir is currently in Phase 3 development for HIV treatment and is being studied as part of a fixed-dose combination with doravirine, as noted by the NIH.
Merck’s New Drug Application (NDA) for DOR/ISL to replace current antiretroviral regimens in virologically suppressed adults has been accepted by the U.S. Food and Drug Administration (FDA), with a target action date of April 28, 2026, as reported by EATG. This regulatory milestone signifies a potential expansion of treatment options for people living with HIV.
What’s Next for DOR/ISL?
The ongoing research and regulatory review of DOR/ISL represent a significant step forward in HIV treatment. Further studies are planned to evaluate the use of DOR/ISL in different populations, including treatment-naive individuals. The availability of a well-tolerated and effective two-drug regimen could greatly improve the quality of life for many people living with HIV. The findings from the MK-8591A-051 study, and ongoing research, will continue to inform clinical practice and treatment guidelines.
This research offers hope for a future with simpler, more effective HIV treatment options. Share your thoughts and experiences in the comments below.
Disclaimer: The information provided in this article is for general knowledge and informational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
