An article in the recent issue of Heptaology illustrates an insightful application of hepatitis C viral dynamic modeling and clinical pharmacology. Guedj et al. (Hepatology 2012 55: 1030-1037) present an HCV dynamic model of viral load versus time during mericitabine therapy. Rather than seeing the clear bi-phasic viral load profile we see with interferon and the protease inhibitors (with characteristic sharp initial drop in viral load), the viral load decline during mericitabine therapy is more complicated: either a slower bi-phasic profile or mono-phasic profile. The authors propose an interesting modeling solution to gain insight into mericitabine’s antiviral activity.