FDA Grants Approval to Merck’s Once-Daily IDVYNSO™ (doravirine/islatravir)
Merck & Co. (NYSE: MRK), known as MSD outside the United States and Canada, has announced that the U.S. Food and Drug Administration has approved IDVYNSO, a novel once-daily, two-drug single-tablet regimen for the treatment of HIV-1 infection in adults. The approval represents a meaningful advancement in HIV care, particularly for patients who are already virologically suppressed and may benefit from a simplified or alternative treatment option.
IDVYNSO combines 100 mg of doravirine, a non-nucleoside reverse transcriptase inhibitor (NNRTI), with 0.25 mg of islatravir, a next-generation nucleoside reverse transcriptase translocation inhibitor (NRTTI). The therapy is indicated as a replacement regimen for adults who are virologically suppressed—defined as having HIV-1 RNA levels below 50 copies per milliliter—on a stable antiretroviral therapy (ART) regimen. Eligible patients must have no history of virologic treatment failure and no known resistance-associated substitutions to doravirine.
The approval of IDVYNSO highlights the continued evolution of HIV treatment, which has transformed over the past decades from complex, multi-pill regimens to more streamlined and patient-friendly options. Today, many individuals living with HIV are achieving long-term viral suppression and living longer, healthier lives. However, as patients age, their treatment needs often become more complex due to the presence of comorbidities and the need to manage multiple medications simultaneously.
Carl Baloney Jr., president and CEO of AIDS United, emphasized the importance of considering these evolving patient needs. He noted that while achieving and maintaining viral suppression remains a primary goal, healthcare providers must also take into account factors such as drug-drug interactions, long-term tolerability, and the broader health challenges associated with aging in people living with HIV. In this context, treatment simplification and diversification are increasingly important components of HIV management.
IDVYNSO is particularly notable because it represents the first two-drug oral regimen that is both non-INSTI (integrase strand transfer inhibitor)–based and free of tenofovir. Most currently available simplified HIV regimens rely on INSTI-based combinations or include tenofovir, which may not be suitable for all patients due to tolerability concerns or comorbid conditions such as renal or bone disease. By offering a different mechanism of action and drug composition, IDVYNSO expands the range of therapeutic options available to clinicians.
Eliav Barr, senior vice president and chief medical officer at Merck Research Laboratories, highlighted the scientific innovation behind the regimen. He explained that islatravir is a next-generation agent with multiple mechanisms of action, including inhibition of viral DNA translocation, while doravirine has an established safety and efficacy profile as an NNRTI. Together, the two agents provide a potent and well-tolerated combination that addresses the needs of patients seeking alternatives to existing therapies.
Barr also noted that the approval marks an important milestone in Merck’s longstanding commitment to HIV research. The company has played a significant role in advancing antiretroviral therapy over several decades, and IDVYNSO represents a continuation of that legacy, with a focus on innovation and patient-centered care.
Clinical evidence supporting the FDA approval of IDVYNSO comes from two Phase 3 trials—Trial 052 and Trial 051—which evaluated the efficacy and safety of switching to the regimen in virologically suppressed adults. Across both studies, a total of 708 participants received once-daily IDVYNSO, including a subset of older adults aged 65 years and above, reflecting the aging HIV population.
In Trial 052, a double-blind study, participants were switched from BIKTARVY to IDVYNSO. A total of 513 individuals were randomized in a 2:1 ratio, with 342 participants switching to IDVYNSO and 171 continuing their baseline regimen. The study population was diverse, with a mean age of 48 years and representation across multiple racial and ethnic groups.
The results demonstrated that IDVYNSO was non-inferior to BIKTARVY in maintaining viral suppression. At Week 48, only 1% of participants in both the IDVYNSO and comparator groups had HIV-1 RNA levels of 50 copies/mL or higher, meeting the primary endpoint. Secondary endpoint analysis showed that 92% of participants who switched to IDVYNSO maintained viral suppression, compared to 94% of those who remained on BIKTARVY.
Trial 051, an open-label study, evaluated switching from a variety of baseline ART regimens to IDVYNSO. A total of 551 participants were randomized, with 366 switching to IDVYNSO and 185 continuing their existing therapy. The study included individuals on integrase inhibitor–based regimens, protease inhibitor–based regimens, and other ART combinations, providing a broad assessment of the regimen’s applicability.
In this study, IDVYNSO again demonstrated non-inferior efficacy. At Week 48, only 1% of participants in the IDVYNSO group experienced virologic rebound, compared to 5% in the group that continued baseline therapy. Additionally, 96% of participants who switched to IDVYNSO maintained viral suppression, compared to 92% in the comparator group. These results suggest that switching to IDVYNSO may offer comparable or even improved virologic control in certain patient populations.
Amy Colson, director of research at the Community Resource Initiative in Boston, highlighted the significance of these findings. She noted that IDVYNSO is the first two-drug regimen of its kind to demonstrate non-inferior efficacy compared to standard oral therapies, including BIKTARVY. This positions it as a viable alternative for patients who may need or prefer to switch treatments while maintaining viral suppression.
The safety and tolerability profile of IDVYNSO was also evaluated in both trials and found to be generally comparable to existing regimens. Rates of adverse events leading to treatment discontinuation were low, with 3% in the IDVYNSO group versus 2% in the BIKTARVY group in Trial 052, and 0.5% versus 2% in Trial 051. Common adverse reactions included diarrhea, dizziness, fatigue, abdominal distention, headache, and weight changes, though most were mild in severity.
Weight changes associated with IDVYNSO were minimal overall, an important consideration given concerns about weight gain with some antiretroviral therapies. In Trial 052, the mean weight change at Week 48 was negligible, while in Trial 051, modest increases were observed but varied depending on prior treatment regimens.
Despite its favorable profile, IDVYNSO carries important safety considerations. Severe skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, have been reported with doravirine-containing regimens. Additionally, Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) has been observed. As with many antiretroviral therapies, potential drug-drug interactions must also be carefully managed.
The regimen is contraindicated for use with strong cytochrome P450 3A (CYP3A) enzyme inducers, as these can reduce drug levels and compromise efficacy. It should also not be co-administered with lamivudine or emtricitabine, as this may lead to reduced effectiveness. Clinicians are advised to review patients’ medication profiles thoroughly to avoid interactions that could result in treatment failure or adverse effects.
Merck has indicated that IDVYNSO will be available in U.S. pharmacies after May 11, providing a new option for patients and healthcare providers seeking alternative HIV treatment strategies. To support access, the company has introduced the Merck Access Program, which offers assistance with insurance navigation, out-of-pocket costs, and co-pay support for eligible individuals. This initiative is designed to ensure that patients who may benefit from IDVYNSO can obtain it without undue financial burden.
The approval of IDVYNSO comes at a time when the HIV treatment landscape is increasingly focused on personalization and long-term management. As patients live longer with the condition, there is growing recognition of the need for therapies that not only maintain viral suppression but also align with broader health goals, including minimizing toxicity, simplifying regimens, and reducing the risk of drug interactions.
By introducing a two-drug, non-INSTI, tenofovir-free regimen, Merck is addressing a gap in current treatment options and offering a new pathway for individualized care. The combination of proven efficacy, a manageable safety profile, and a novel mechanism of action positions IDVYNSO as an important addition to the HIV treatment arsenal.
Looking ahead, the introduction of IDVYNSO may also stimulate further innovation in the field, encouraging the development of additional simplified regimens and next-generation therapies. As research continues to explore new mechanisms and treatment strategies, the ultimate goal remains the same: to improve the quality of life for people living with HIV and, eventually, to achieve a cure.
In summary, the FDA approval of IDVYNSO represents a significant milestone in HIV treatment. Supported by robust Phase 3 data and designed to meet the evolving needs of patients, the regimen offers a new, effective, and flexible option for maintaining viral suppression. As it becomes available in clinical practice, it is expected to play a valuable role in advancing personalized, long-term HIV care.
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