YAMASA CORPORATION (Head Office: Choshi City, Chiba Prefecture; President: Naoyuki Ishibashi; hereinafter “Yamasa”) is pleased to announce that a new pharmaceutical product incorporating a compound developed through its long-standing research and external collaborations has been approved by the U.S. Food and Drug Administration (FDA).

The approved product is IDVYNSO® (generic name: doravirine/islatravir hydrate combination tablets), an HIV-1 therapeutic agent developed by Merck & Co., Inc., Rahway, NJ, USA (hereinafter “MSD”). The product was approved in Japan on March 6, 2026, and subsequently in the United States on April 20, 2026.
This medicine contains two active pharmaceutical ingredients: doravirine and islatravir.
Doravirine, developed by MSD, is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that has already been approved for the treatment of HIV-1 infection.
In contrast, islatravir (4′-ethynyl-2-fluoro-2′-deoxyadenosine, EFdA) is a potent next-generation nucleoside reverse transcriptase inhibitor (NRTI), classified within the novel class of nucleoside reverse transcriptase translocation inhibitors (NRTTIs). Islatravir exerts its antiviral activity through multiple mechanisms: it induces structural modifications in viral DNA, resulting in immediate chain termination, and it prevents the translocation of reverse transcriptase to the next nucleotide-binding position required for DNA elongation. Through these dual and synergistic mechanisms, islatravir effectively inhibits reverse transcriptase-mediated DNA synthesis and suppresses HIV-1 replication. Owing to this potent and multifaceted mechanism of action, islatravir is expected to provide sustained antiviral efficacy at low dosing levels.
Since the 1990s, Yamasa has pursued the application of nucleic acid-related compounds in antiviral therapeutics. In the 2000s, the company contributed to the molecular design, synthesis, and pharmacological evaluation of islatravir in collaboration with academic and external research partners. In 2012, Yamasa entered into a licensing agreement with MSD, which subsequently advanced the clinical development of islatravir as an HIV-1 therapeutic, culminating in the present regulatory approvals.

In parallel with its research on microorganisms and fermentation associated with soy sauce production, Yamasa has conducted extensive research and manufacturing of nucleic acid-related substances, originating from its work on nucleotide-based umami seasonings. Since establishing industrial-scale production technologies for 5′-inosinic acid and 5′-guanylic acid in the 1950s, the company has continuously advanced specialized technologies in nucleic acid chemistry. These technologies have been applied across a wide range of fields, including active pharmaceutical ingredients (APIs) and intermediates, food additives, cosmetics, and other industrial applications.
Yamasa considers the invention of islatravir as a notable example of how its research and development in the field of nucleic acids has contributed to advancements in human health and medical science.

The FDA approval represents a significant milestone in global efforts to expand therapeutic options for HIV-1 infection. Yamasa takes great pride in having contributed to this achievement and expresses its sincere appreciation to MSD and all collaborators whose efforts made this approval possible.