PSI-7851 has demonstrated potent in vitro anti-HCV activity with EC50 values of 90 +/- 60 nM, which is approximately 15- to 20-fold more potent than Pharmasset's first generation nucleoside polymerase inhibitor, R7128
I believe IDX-184 has a lower (better) EC50 compared to R7128. however both are plenty potent, so this disparity is unlikely to be clinically meaningful unless the lower dose of the idenix compound translates into a better SE profile