Merck, known as MSD outside the United States and Canada, has shared topline results from its pivotal double-blind Phase 3 trial evaluating the investigational once-daily oral two-drug single-tablet regimen of doravirine/islatravir (DOR/ISL 100 mg/0.25 mg) in adults with HIV-1 infection who have not previously received antiretroviral treatment. The trial, designated MK-8591A-053, met its primary efficacy goal, showing that the percentage of participants with HIV-1 RNA levels below 50 copies per milliliter at Week 48 was comparable to the once-daily three-drug regimen of bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF 50 mg/200 mg/25 mg). The safety profile of DOR/ISL was also consistent with BIC/FTC/TAF, meeting the trial’s primary safety objectives.

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Merck plans to present a detailed analysis of the trial results at an upcoming scientific conference and will submit regulatory applications based on these findings. The U.S. Food and Drug Administration has accepted the New Drug Application for DOR/ISL as a treatment option for adults living with HIV-1, with a target action date of April 28, 2026, under the Prescription Drug User Fee Act. In the United States, doravirine is already approved for use in adults with HIV-1 either as a single agent in combination with other antiretrovirals under the brand name PIFELTRO or as part of a single-tablet regimen, DELSTRIGO, which combines doravirine, lamivudine, and tenofovir disoproxil fumarate.

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Dr. Eliav Barr, senior vice president, head of global clinical development and chief medical officer of Merck Research Laboratories, said the company is encouraged by the Phase 3 results. He highlighted that DOR/ISL is the first two-drug regimen without an integrase inhibitor to demonstrate non-inferior efficacy and safety compared with a three-drug INSTI-based regimen in treatment-naïve adults. He emphasized that the findings support DOR/ISL as a promising treatment option both for people who are virally suppressed seeking a switch in therapy and for those starting antiretroviral treatment for the first time.

The MK-8591A-053 study is a randomized, active-controlled, double-blind trial that enrolled 537 participants who were assigned in a 1:1 ratio to either the DOR/ISL or BIC/FTC/TAF regimens for a 48-week assessment period. The study continues through Week 144 with data planned for Week 96 and offers participants the opportunity to join an open-label extension, receiving DOR/ISL until Week 240 or until the regimen becomes commercially available. Primary endpoints include efficacy measured by the percentage of participants with HIV-1 RNA levels under 50 copies per milliliter and safety measured by adverse events and discontinuations due to side effects at Week 48.

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