Ribavirin Improves Early Responses to Peginterferon Through Improved Interferon Signaling

Background & Aims: The therapeutic mechanisms of ribavirin for hepatitis C are unclear. Microarray analyses have shown that ribavirin increases induction of interferon-stimulated genes. We evaluated viral kinetics, serum cytokine expression, and viral mutagenesis during early stages of peginterferon therapy with and without ribavirin. Methods: Fifty patients with chronic hepatitis C virus (HCV) infection genotype 1 were randomly assigned to groups that were given peginterferon α-2a, with or without ribavirin, for 4 weeks; all patients then received an additional 44 weeks of combination therapy. First- and second-phase viral kinetics were evaluated. Serum levels of interferon-γ-inducible protein-10 (IP10), monokine induced by interferon-γ, and monocyte chemoattractant protein 1 were quantified as measures of the interferon-stimulated genes response. NS5A and NS5B were partially sequenced, and mutation rates were calculated. Results: The first-phase decrease in HCV RNA was similar between groups. Patients who received ribavirin had a more rapid second-phase decrease, compared with patients who did not receive ribavirin-particularly those with an adequate first-phase decrease (0.61 vs 0.35 log10 IU/mL/week; P = .018). At 12 hours, fold induction of serum IP10 was higher in patients given the combination therapy than those given peginterferon only (7.6- vs 3.8-fold; P = .01); however, the difference was greatest in patients with an adequate first-phase decrease in HCV RNA. IP10-induction correlated with first- and second-phase kinetics and with ribavirin serum concentrations on day 3. HCV mutation rates were similar between groups. Conclusions: Ribavirin improves the kinetics of the early response to therapy in patients with an adequate initial response to peginterferon. Induction of interferon-stimulated cytokines correlates with viral kinetics following ribavirin therapy, suggesting that ribavirin promotes interferon signaling.