In a significant advancement for the global HIV treatment landscape, pharmaceutical giants Gilead Sciences and Merck have reported successful Phase 3 results for their investigational once-weekly oral antiretroviral regimen. The combination, pairing Merck’s next-generation nucleoside analog islatravir with Gilead’s first-in-class capsid inhibitor lenacapavir, has demonstrated robust efficacy in maintaining viral suppression among adults already living with HIV.
The findings, presented at the 26th International AIDS Conference, offer a glimpse into a future where the daily burden of HIV management—a routine that has defined the standard of care for decades—could be replaced by a once-weekly tablet. With a combined total of 1,209 participants across two major trials, ISLEND-1 and ISLEND-2, the data suggests that this novel combination is not only effective but also highly favored by patients seeking to reduce the "pill burden" of their treatment.
The Core Data: Clinical Efficacy and Safety
The primary objective of the ISLEND clinical program was to determine whether a weekly 2 mg dose of islatravir combined with a 300 mg dose of lenacapavir could maintain virologic suppression as effectively as the current gold standard, Gilead’s Biktarvy.
ISLEND-1: The Double-Blind Benchmark
In the double-blind ISLEND-1 trial, researchers evaluated the efficacy of the weekly regimen against the daily standard of care. The results were striking: at Week 48, zero participants in the investigational group exhibited HIV-1 RNA levels at or above 50 copies/mL. In the comparator arm—patients continuing on daily Biktarvy—the rate of virologic suppression failure was a negligible 0.3%.
Safety profiles were equally comparable. Treatment-related adverse events (TRAEs) were reported by 13.5% of those on the weekly regimen and 13.2% of those on the daily regimen. Common side effects, such as nausea and headache, were reported in only 3% of the ISL/LEN cohort. Serious adverse events remained low and balanced across both groups, occurring in 5.3% of the experimental arm and 4.6% of the control arm.
ISLEND-2: Real-World Comparisons
ISLEND-2 utilized an open-label design, allowing for a broader comparison against a range of standard antiretroviral regimens. Again, the efficacy was consistent: only 0.3% of participants on the weekly regimen experienced viral rebound, compared to 1.3% of those who remained on their baseline therapy.
While the reported rate of adverse events was higher in the ISL/LEN group (18% vs. <1% in the control arm), investigators noted that this discrepancy is largely attributable to the study design. Participants in the standard-of-care arm had been on their existing treatments for at least six months, effectively moving past the window when initial side effects typically present. Consequently, the low discontinuation rates for adverse events—just 2% for the new regimen—provide a more accurate reflection of the drug’s tolerability.
Chronology of Development
The path to this breakthrough has been a methodical, multi-year endeavor marked by rigorous testing and strategic refinement.
- October 2024: Gilead and Merck released positive Phase 2 data. A study of 104 virologically suppressed adults showed that the weekly ISL/LEN combination was non-inferior to Biktarvy, with no participants showing viral rebound at 48 weeks. Adherence in this study exceeded 98%.
- November 2024: Dr. Amy Colson presented Phase 2 findings at HIV Glasgow, sparking vital industry discussions regarding the clinical management of patients switching away from tenofovir-based regimens, specifically regarding hepatitis B screening and immunization.
- April 2026: The FDA approved Merck’s Idvynso (doravirine/islatravir), signaling regulatory confidence in the islatravir molecule.
- June 2026: Gilead and Merck released the topline results of the ISLEND trials, confirming that the weekly regimen successfully met its primary endpoints.
- July 2026: Detailed data from the ISLEND-1 and ISLEND-2 trials were formally presented at the 26th International AIDS Conference, marking the official entry of the regimen into the late-stage regulatory pipeline.
Supporting Data: Why "Once-Weekly" Matters
The shift from a seven-pill-a-week schedule to a single tablet represents a fundamental change in the patient experience. According to the HIV Patient Perspective of Regimen Change instrument utilized in the ISLEND-2 study, a significant majority of participants expressed higher satisfaction and lower psychological burden with the weekly regimen compared to their previous daily therapies.
The pharmacokinetic profiles of the two drugs are the secret to this success. Islatravir, a nucleoside reverse transcriptase translocation inhibitor (NRTTI), possesses a long half-life, while lenacapavir, a first-in-class capsid inhibitor, interferes with multiple stages of the HIV viral lifecycle, including capsid-mediated nuclear import and assembly. Together, these mechanisms allow for sustained therapeutic levels in the blood over a seven-day period.
The Competitive Landscape and Official Responses
The HIV treatment market is currently dominated by Gilead’s Biktarvy, which commanded over 52% of the U.S. market in early 2026. However, the market is rapidly evolving.
Gilead’s Portfolio Strategy
Gilead is playing a double game, simultaneously protecting its Biktarvy franchise while aggressively innovating. The company is also advancing a daily oral bictegravir/lenacapavir regimen (ARTISTRY trials) as a potential successor. By developing both daily and weekly oral options, Gilead aims to retain its market dominance even as patents on older drugs approach their expiration dates.
The Challenge from Injectables
The primary competitive threat to oral regimens remains long-acting injectables. GSK’s ViiV Healthcare has seen significant success with Cabenuva, an injectable given every one or two months. While injectables offer the ultimate convenience of "set it and forget it" care, they require frequent clinic visits for administration. The ISL/LEN regimen occupies a unique "middle ground": it offers the convenience of reduced frequency with the autonomy of an at-home oral medication.
Implications: The Future of HIV Management
Clinical Considerations
The transition to a weekly oral regimen necessitates a shift in clinical practice. As noted by experts during the HIV Glasgow summit, because the current standard of care—including Biktarvy—often contains tenofovir (which has anti-hepatitis B activity), physicians must ensure that patients switching to an ISL/LEN regimen are appropriately screened for hepatitis B and, if necessary, vaccinated. This nuance will be critical for clinical guidelines if and when the FDA grants full approval.
Market and Economic Impact
The financial stakes are immense. Biktarvy generated $14.3 billion in 2025 alone. With generic competition for Biktarvy not expected in the U.S. until 2036, Gilead is in a position of strength. By introducing a weekly regimen, the company is effectively cannibalizing its own product to set a new standard, a move that preemptively wards off generic entrants and establishes a new, higher-value tier of treatment.
Empowering Patients
Beyond the balance sheets and clinical efficacy percentages, the most profound implication of the ISLEND trials is the impact on quality of life. For many people living with HIV, the daily pill is a constant, sometimes stressful reminder of their status. Reducing that frequency by 85% could significantly improve adherence rates and reduce the "pill fatigue" that some patients experience over years of treatment.
As the industry looks toward the next decade, the Gilead-Merck collaboration serves as a blueprint for the future of chronic disease management. By leveraging potent, long-acting molecules to bridge the gap between daily pills and long-acting injectables, the researchers behind ISLEND have potentially unlocked a new era of HIV care—one defined by simplicity, clinical excellence, and patient-centered convenience.
Should the FDA follow the positive trend of the trial data, the once-weekly oral regimen could reach patients as early as 2027, forever altering the daily lives of those managing HIV worldwide.
About the Author
