EIDD-2749 (4-FlU) is an orally bioavailable ribonucleoside analog that potently inhibits viral RNA-dependent RNA polymerase (RdRp). It demonstrates broad-spectrum antiviral efficacy in vitro and in vivo against respiratory syncytial virus (RSV), SARS-CoV-2, and lethal influenza viruses, including pandemic and highly pathogenic avian strains.