Gilead Sciences Inc. (NASDAQ:GILD) and Merck & Co. Inc. (NYSE:MRK) on Tuesday reported detailed Phase 3 results showing their investigational once-weekly oral HIV regimen of islatravir and lenacapavir (ISL/LEN) maintained viral suppression through 48 weeks in adults switching from daily antiretroviral therapy.
The once-weekly single-tablet regimen met the primary endpoint in both Phase 3 studies, demonstrating non-inferior efficacy to standard daily treatment.
ISL/LEN is being developed as what could become the first once-weekly oral HIV regimen, potentially changing the standard of care from daily to weekly dosing.
The data, which will be presented at the International AIDS Conference (AIDS 2026), will support planned regulatory submissions.
ISLEND-1 Trial Demonstrates High Efficacy
In the ISLEND-1 trial, zero participants on once-weekly ISL/LEN had HIV-1 RNA levels reaching 50 copies/mL or higher at Week 48, compared to 0.3% of participants who remained on daily Biktarvy.
HIV-1 RNA levels (viral load) measure the amount of genetic material from the virus in the blood. It assesses disease progression and treatment effectiveness.
Treatment-related adverse events were reported in 13.5% of ISL/LEN participants and 13.2% of Biktarvy participants, with nausea and headache being the most frequent in both arms.
Discontinuations due to side effects were low at 2% and 1.7%, respectively.
ISLEND-2 Confirms Non-Inferior Care
Results from the open-label ISLEND-2 trial similarly showed non-inferiority, with 0.3% of participants receiving weekly ISL/LEN displaying HIV-1 RNA at 50 copies/mL or higher versus 1.3% taking daily standard care regimens.
Treatment-related adverse events occurred in 18% of ISL/LEN patients compared to under 1% in standard care, primarily consisting of headache, nausea, and diarrhea. Discontinuations due to side effects remained low across both arms.
Patient Satisfaction And Regulatory Submissions
Across both ISLEND studies, CD4+ T-cell counts, lymphocyte levels, and body weight remained stable through Week 48 without new safety concerns identified.
Participants who switched to once-weekly oral ISL/LEN reported lower treatment burden and higher overall regimen satisfaction than those on daily care.
Price Action: Merck shares were up 0.87% at $125.48, and Gilead Sciences shares were down 2.62% at $129.72 at the time of publication on Tuesday, according to Benzinga Pro data.
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