Temporal Dynamics of a Predominant Protease Inhibitor–Resistance Mutation in a Treatment-Naive, Hepatitis C Virus–Infected Individual

The dramatic antiviral activities of drugs that specifically inhibit hepatitis C virus replication can be tempered by baseline mutations that confer resistance. We describe the kinetics of an R155K mutation in hepatitis C virus (HCV) NS3 protease known to confer resistance to specific protease inhibitors in an individual coinfected with human immunodeficiency virus-1 and HCV. Longitudinal sequences revealed changes in the relative frequency with which this variant was observed independent of HCV replication levels, illustrating that this mutation coexists with wild-type strains in vivo in the absence of drugs. The persistence of drug-resistance mutations argues for baseline resistance genotyping at the time therapy is initiated to accurately predict the efficacy of treatment.