Lomibuvir (VX-222) is a selective, non-nucleoside allosteric inhibitor of HCV NS5B polymerase (RdRp) with a Kd of 17 nM. Lomibuvir inhibits the 1b/Con1 HCV subgenomic replicon with an EC 50 of 5.2 nM. Lomibuvir preferentially inhibits elongative RNA synthesis rather than de novo -initiated RNA synthesis [1].