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Merck & Co Inc. (MRK)
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Merck & Co. Inc. Announces Promising Phase 3 Trial Results for HIV Treatment

Last updated: March 12, 2025
Taurigo

March 12, 2025 – Merck & Co., Inc. (NYSE: MRK) has unveiled encouraging data from two pivotal Phase 3 clinical trials for its investigational oral two-drug regimen of doravirine/islatravir (DOR/ISL). The trials demonstrated that DOR/ISL maintained HIV-1 viral suppression at Week 48 in adults who were previously virologically suppressed on standard antiretroviral therapy. The results are set to be presented in late-breaking oral sessions at the 32nd Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco.

1. Overview of the Trials

The two trials, MK-8591A-052 and MK-8591A-051, evaluated the efficacy and safety of DOR/ISL (100mg/0.25mg) as a switch option for adults with HIV-1 infection. In MK-8591A-052, participants switched from bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF) to DOR/ISL, while MK-8591A-051 involved switching from baseline antiretroviral therapy (bART).

Trial MK-8591A-052 Highlights

In the double-blind MK-8591A-052 trial, 1.5% of participants switched to DOR/ISL had a viral load of ≥50 copies/mL at Week 48, compared to 0.6% on BIC/FTC/TAF. The primary endpoint demonstrated non-inferiority, with 91.5% of participants on DOR/ISL maintaining viral suppression (HIV-1 RNA <50 copies/mL) compared to 94.2% on the comparator regimen.

Trial MK-8591A-051 Highlights

The open-label trial MK-8591A-051 showed that 1.4% of participants on DOR/ISL had a viral load ≥50 copies/mL at Week 48, while 4.9% on bART experienced the same. Notably, 95.6% of participants on DOR/ISL maintained viral suppression compared to 91.9% on bART, confirming the efficacy of the new regimen.

Safety Profile

Across both trials, DOR/ISL exhibited a safety profile comparable to the comparator regimens. No treatment-emergent resistance was observed, and the mean percent change in total lymphocyte and CD4 counts were similar between DOR/ISL and the comparator therapies. The most common adverse events reported were arthralgia, COVID-19, nasopharyngitis, and fatigue, with no significant safety concerns arising from the trials.

2. Expert Insights

Professor Chloe Orkin, Dean for Healthcare Transformation at Queen Mary University of London, expressed enthusiasm over the potential of DOR/ISL as a new daily treatment option for those living with HIV, particularly considering the evolving health needs of aging populations with comorbidities.

Dr. Eliav Barr, Merck's Senior Vice President and Chief Medical Officer, emphasized the significance of DOR/ISL as the first two-drug regimen without an integrase inhibitor to demonstrate comparable efficacy and safety to the three-drug regimen BIC/FTC/TAF. He noted Merck's long-standing commitment to advancing HIV treatment through innovative research and development.

3. Regulatory Plans and Future Prospects

Merck plans to initiate submissions for marketing authorization to regulatory agencies by mid-2025. The company aims to build on its decades-long legacy in HIV research, with ongoing studies exploring the potential of islatravir in various treatment regimens, including once-weekly options.

As Merck continues to innovate in the HIV treatment landscape, the positive results from the DOR/ISL trials mark a significant step towards providing new and effective treatment options for those living with HIV.

For further updates, industry stakeholders are encouraged to follow the developments presented at CROI and subsequent regulatory submissions by Merck.

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