4'-Ethynyl-2-fluoro-2'-deoxyadenosine, MK-8591: a novel HIV-1 reverse transcriptase translocation inhibitor

Curr Opin HIV AIDS. 2018 Jul;13(4):294-299. doi: 10.1097/COH.0000000000000467.


Purpose of review: 4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a nucleoside reverse transcriptase inhibitor (NRTI) with a novel mechanism of action, unique structure, and amongst NRTIs, unparalleled anti-HIV-1 activity. We will summarize its structure and function, antiviral activity, resistance profile, and potential as an antiretroviral for use in the treatment and preexposure prophylaxis of HIV-1 infection.

Recent findings: EFdA is active against wild-type (EC50 as low as 50 pmol/l) and most highly NRTI-resistant viruses. The active metabolite, EFdA-triphosphate, has been shown to have a prolonged intracellular half-life in human and rhesus (Rh) blood cells. As a result, single drug doses tested in simian immunodeficiency virus mac251-infected Rh macaques and HIV-1-infected individuals exhibited robust antiviral activity of 7-10 days duration. Preclinical studies of EFdA as preexposure prophylaxis in the Rh macaque/simian/human immunodeficiency virus low-dose intrarectal challenge model have shown complete protection when given in clinically relevant doses.

Summary: EFdA is a novel antiretroviral with activity against both wild-type and NRTI-resistant viruses. As a result of the prolonged intracellular half-life of its active moiety, it is amenable to flexibility in dosing of at least daily to weekly and perhaps longer.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Animals
  • Anti-HIV Agents / chemistry*
  • Anti-HIV Agents / pharmacology*
  • Deoxyadenosines / chemistry*
  • Deoxyadenosines / pharmacology*
  • HIV Infections / drug therapy
  • HIV Infections / virology
  • HIV Reverse Transcriptase / antagonists & inhibitors
  • HIV Reverse Transcriptase / metabolism
  • HIV-1 / drug effects
  • HIV-1 / enzymology
  • HIV-1 / genetics
  • HIV-1 / physiology
  • Humans
  • Reverse Transcriptase Inhibitors / chemistry*
  • Reverse Transcriptase Inhibitors / pharmacology*


  • Anti-HIV Agents
  • Deoxyadenosines
  • Reverse Transcriptase Inhibitors
  • reverse transcriptase, Human immunodeficiency virus 1
  • HIV Reverse Transcriptase
  • 4'-ethynyl-2-fluoro-2'-deoxyadenosine