Several host (age, sex, race, fibrosis stage, interleukin 28B polymorphism) and viral factors (hepatitis C virus [HCV] genotype, viral load) allow estimating the response to interferon-based therapies (which includes first-generation protease inhibitors) before treatment. However, treatment should not be denied to any patient based on unfavorable factors alone. Metabolic conditions associated with poor response (diabetes, insulin resistance, obesity) and alcohol abuse can be influenced before starting treatment. "On-treatment" predictors of response allow treatment to be tailored to the individual need of the patient. Patients with undetectable HCV RNA after 4 weeks (rapid virologic response [RVR]) have the highest chance for cure (>85%) both by dual and triple therapy. For triple therapy, the decision to shorten treatment requires that the virus remains undetectable for an additional 8 (telaprevir) to 20 (boceprevir) weeks (extended RVR). Based on viral kinetics, an even earlier prediction after 2 weeks of treatment with direct acting antivirals appears feasible.
