Merck (NYSE:MRK), known as MSD outside the U.S. and Canada, announced today that the U.S. Food and Drug Administration (FDA) has approved IDVYNSO™, a new single-tablet antiretroviral regimen.
The approval offers a streamlined treatment option for adults living with HIV-1 who are currently virologically suppressed on a stable regimen, marking a significant milestone in Merck’s infectious disease portfolio.
IDVYNSO (pronounced ihd-VIHN-soh) is a once-daily combination of 100 mg doravirine (a non-nucleoside reverse transcriptase inhibitor) and 0.25 mg islatravir (a first-in-class nucleoside reverse transcriptase translocation inhibitor).
The tablet is specifically indicated as a replacement regimen for patients with HIV-1 RNA levels below 50 copies per mL who have no history of treatment failure or resistance to doravirine.
The approval is a pivotal moment for Merck’s HIV pipeline, as it validates the use of a lower dose of islatravir (0.25 mg).
Development had previously faced hurdles due to concerns regarding lymphocyte and T-cell count decreases at higher doses, but the refined lower-dose combination demonstrated a favorable safety and efficacy profile in clinical trials.
As a complete two-drug regimen, IDVYNSO is not recommended for co-administration with other antiretroviral medications.
The FDA issued several safety precautions regarding the new treatment.
Merck expects IDVYNSO to be available in pharmacies across the United States shortly after May 11, 2026.
This approval positions Merck to compete more effectively in the "switch" market for stable HIV patients, currently dominated by multi-drug regimens.