Islatravir (4′-ethynyl-2-fluoro-2′-deoxyadenosine, EFdA, or MK-8591) is an investigational drug for the treatment of

HIV infection The human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a preventable disease. It can ...

. It is classified as a nucleoside reverse transcriptase translocation inhibitor (NRTTI). Merck is developing a subdermal drug-eluting implant to administer islatravir. In 2021,

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

placed a partial clinical hold for several studies under Islatravir. The reason was a decline in CD4 T cells under therapy. Merck announced to restart the study program in 2023 with a decreased dose, however studies of islatravir for

pre-exposure prophylaxis Pre-exposure prophylaxis (PrEP), is the use of medications to prevent the spread of disease in people who have not yet been exposed to a disease-causing agent. Vaccination is the most commonly used form of pre-exposure prophylaxis; other forms of ...

(PrEP) will be discontinued. In 2024, results from a phase II study combining islatravir with lenacapavir indicated that the regimen shows promise as a possible weekly oral regimen.

Biological activity

Islatravir has activity against HIV in

animal model An animal model (short for animal disease model) is a living, non-human, often genetic-engineered animal used during the research and investigation of human disease, for the purpose of better understanding the disease process without the risk of ha ...

s, and is being studied clinically for HIV treatment and prophylaxis. Islatravir is a

nucleoside Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (ribose or 2'-deoxyribose) whereas a nucleotid ...

reverse transcriptase translocation inhibitor (NRTTI) that unlike other such inhibitors, inhibits HIV through multiple mechanisms, providing rapid suppression of the virus, when tested in macaques and mice. Nevertheless, there are HIV strains resistant to islatravir and research is ongoing.

References

{{HIVpharm Nucleoside analog reverse transcriptase inhibitors Ethynyl compounds Fluoroarenes Hydroxymethyl compounds