Merck (MRK) has received FDA acceptance for its New Drug Application covering the once-daily HIV combination therapy doravirine/islatravir, with regulators establishing an April 28, 2026 PDUFA action date for what could become the first two-drug treatment regimen that doesn’t include integrase inhibitors.
This regulatory submission addresses a considerable gap in HIV care by proposing a streamlined treatment approach that may decrease pill burden and minimize long-term adverse effects for patients who have achieved viral suppression with existing therapies.
Key Takeaways
- FDA sets April 28, 2026 PDUFA date for Merck HIV combo
- First potential two-drug regimen without integrase inhibitor class
- Phase 3 trials showed non-inferior efficacy versus standard treatments
Market Context
Within the roughly $32 billion worldwide HIV therapeutics sector, Merck’s HIV portfolio faces competition from industry leaders Gilead Sciences and ViiV Healthcare 1. Revenue from the company’s current HIV medications Pifeltro and Delstrigo exceeded $400 million across recent reporting periods.
This doravirine/islatravir combination would stand apart from prevailing three-drug standard treatments by providing an innovative two-drug strategy that excludes integrase strand transfer inhibitors.
Clinical Development Progress
Two crucial Phase 3 studies, designated MK-8591A-051 and MK-8591A-052, provide the 48-week efficacy data supporting this New Drug Application 1. Each trial established non-inferior performance when compared against baseline antiretroviral therapy and bictegravir/emtricitabine/tenofovir alafenamide treatment, respectively.
More than 1,000 adult participants with virologically suppressed HIV-1 infection were included across these studies. The safety characteristics observed were broadly consistent with current treatment options in both investigations.
Management Commentary
“Merck has been at the forefront of HIV research for more than 35 years and we are pleased to continue our work to innovate and deliver new options that aim to meet the needs of the HIV community,” said Dr. Eliav Barr, senior vice president of global clinical development at Merck Research Laboratories 1.
“The health needs of people living with HIV often change over time – whether it’s managing comorbidities or navigating complex medication regimens. We believe DOR/ISL, if approved, will represent an important new complete regimen option designed to help meet their diverse needs.”
Broader HIV Pipeline
Beyond this current submission, Merck maintains active development of several HIV programs. The pharmaceutical company is investigating islatravir combined with Gilead’s lenacapavir as a prospective once-weekly oral therapy 1.
Other ongoing Phase 3 investigations encompass studies involving treatment-naive patients and extension trials assessing long-term safety and efficacy outcomes for the doravirine/islatravir combination.
Regulatory Outlook
FDA acceptance of this application marks an important achievement following earlier regulatory hurdles encountered during islatravir development programs. Previous studies faced temporary suspension due to lymphocyte reduction issues, but work resumed following protocol modifications incorporating reduced dosing 2.
Upon potential approval, this combination therapy would equip healthcare providers with an additional option for streamlining HIV treatment protocols while preserving viral suppression effectiveness.
Not investment advice. For informational purposes only.
References
1Merck (July 10, 2025). “U.S. FDA Accepts New Drug Application for Merck’s Doravirine/Islatravir”. Merck.com. Retrieved April 21, 2026.
2Max Bayer (April 30, 2023). “Merck reveals HIV combo trial is back in the running after FDA partial hold lifted”. EATG. Retrieved April 21, 2026.
3“FDA Accepts Merck’s Filing for Two-Drug, Once-Daily HIV Pill” (July 11, 2025). Yahoo Finance. Retrieved April 21, 2026.
4MD Magazine Staff (September 20, 2019). “FDA Approves Duo of HIV Medications”. HCPLive. Retrieved April 21, 2026.
5Alex Keown (August 31, 2018). “Updated: Merck Scores FDA Approval for Two New HIV Treatments”. BioSpace. Retrieved April 21, 2026.