While the impact of long-term IFN-α administration on cytochrome P450 isozyme 1A2 (CYP1A2) expression or pharmacokinetics of its prototypical substrate theophylline was convincingly shown in vitro [10], in healthy volunteers [11], and also in patients with viral hepatitis [12,13], the effect on the most prominent drug-metabolizing enzyme CYP3A4 is contradicting. Here, CYP3A4 is linked to animal viral hepatitis.