Core Insights - Merck (MRK) has received FDA acceptance for the new drug application (NDA) for its investigational two-drug regimen doravirine/islatravir (DOR/ISL) aimed at treating virologically suppressed adults with HIV-1 infection, with a decision expected by April 28, 2026 [1][7] Drug Efficacy and Studies - If approved, DOR/ISL would be the first non-integrase inhibitor-based two-drug regimen demonstrating comparable efficacy and safety to the current three-drug standard, BIC/FTC/TAF, in phase III studies [2] - The NDA is supported by data from two pivotal phase III studies (MK-8591A-051 and MK-8591A-052), which showed that DOR/ISL (100 mg/0.25 mg) was non-inferior to comparator antiretroviral therapies in adults with virologically suppressed HIV-1 [3] Ongoing Research and Collaborations - Merck is continuing its HIV research with additional trials, including MK-8591A-053 and MK-8591A-054, which evaluate DOR/ISL in treatment-naïve individuals and those from earlier studies, respectively [9][10] - The company is collaborating with Gilead Sciences (GILD) to evaluate islatravir in combination with GILD's lenacapavir in a phase II study for HIV treatment [10] Stock Performance - Year to date, Merck's shares have decreased by 15.5%, contrasting with a 0.2% rise in the industry [4]

Core Viewpoint - Gilead Sciences' stock experienced a decline of over 2% following negative news regarding its investigational HIV treatment program, contrasting with a 0.6% gain in the S&P 500 index [1][2]. Regulatory Action - The U.S. Food and Drug Administration (FDA) has ordered a halt to Gilead's clinical trials involving a two-drug combination aimed at treating HIV [2]. - The FDA's decision was prompted by findings of low CD4+ T-cell levels in some trial participants, although the cause of these deficiencies remains unclear [4]. Drug Information - The two drugs involved are GS-1720, a weekly administered treatment, and GS-4182, a pill version of lenacapavir (commercially known as Sunlenca) [5]. - Gilead is also testing these drugs against its existing HIV treatment, Biktarvy, in various stages of clinical trials [4]. Pipeline and Future Prospects - Despite the FDA's hold, Gilead has indicated that it is developing numerous other HIV combination treatments that are not impacted by this regulatory action [5]. - The company maintains a robust pipeline with 58 investigational programs, suggesting that the FDA's pause may not represent a significant setback for Gilead [6].