AVG-233 is a potent, orally active RNA dependent RNA polymerase (RdRp) inhibitor. AVG-233 prevents initiation of the viral polymerase complex at the promoter. AVG-233 binding site is present in the L 1-1749 fragment. AVG-233 has nanomolar activity against both RSV strains and clinical RSV isolates ( EC 50 =0.14-0.31 μM). AVG-233 can be used for research of respiratory syncytial virus (RSV). In Vitro AVG-233 (1-100 μM) blocks 3´RNA extension elongation but does not interfere with 3´RNA extension by up to three nucleotides after de novo initiation from the promoter or back-priming. AVG-233 (20 μM) reduces virus yield of RSV A2-L19F (EC 50 =0.31 μM), RSV strain 2-20 (EC 50 =0.14 μM) and RSV clinical isolate 718 (EC 50 =0.2 μM). AVG-233 (1.25-40 μM; 0-300 s) suppresses RNA synthesis by the L1-1749 fragment in a dose-dependent manner with an IC 50 value of 13.7 μM. AVG-233 bounds L and the L 1-1749 fragment with similar affinities (dissociation constants (KD’s) are 38.3 μM and 53.1 μM, respectively). MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo AVG-233 (50-100 mg/kg; i.g.; once) decreases lung viral load in the RSV mouse model. AVG-233 (2-20 mg/kg; i.v. and p.o.; once; male CD-1 mice) has good orally bioavailable and the maximum plasma concentration about 2 μM . MCE has not independently confirmed the accuracy of these methods. They are for reference only. Animal Model: Female Balb/cJ mice with recRSV-mKate xenograftDosage: 50 and 100 mg/kg Administration: Oral gavage; once Result: Reduced in lung viral load of 0.89 log 10 TCID 50 (median tissue culture infectious dose)/mL. Animal Model: Male CD-1 mice (27-29 g) Dosage: 2 mg/kg (i.v.) and 20 mg/kg (p.o.) Administration: Intravenous injection and oral administration; once, obtains blood samples at pre-dose and 0.083, 0.25, 0.5, 1, 2, 4, 8, and 24 h post-dosing Result: 1.19 Route Dose T max C max AUC 0-∞ CL/F T 1/2 Bioavailability mg/kg h nmol/ml h×nmol/ml liters/h/kg h % Oral 20 1 2.17 5.95 6.98 5.28 33.8 Form:Solid