Plasma HCV RNA levels were assessed using a commercially available reverse-transcriptase polymerase chain reaction (PCR) assay (Roche COBAS TaqMan HCV/HPS assay, v2.0). The linear range of the assay is from 25 IU/mL (LOQ) to 391,000,000 IU/mL of HCV RNA (upper LOQ). The lower p38 MAPK phosphorylation LOD of the assay is 10 IU/mL. Baseline HCV RNA was defined as the mean of two HCV RNA values: one measured 2-7 days before dosing and the other measured on the first day of dosing. If one of these HCV RNA values was missing, the single available value was used. The tolerability of vaniprevir was monitored from the first study dose through

to 14 days after the last study dose (i.e., day 42) by the clinical evaluation of adverse events (AEs) reported by the patient and by repeated measurements of vital signs (e.g., heart rate, blood pressure, respiration rate, and oral temperature), 12-lead electrocardiographs (ECGs), physical examinations, body weight, and standard laboratory

safety tests (i.e., blood chemistry, hematology, and urinalysis). The presence of resistance-associated amino-acid variants (RAVs) was assessed during the first 42 days of dosing using a population Transferase inhibitor resistance-sequencing assay with a detection limit of 1,000 IU/mL for both genotypes 1a and 1b. Baseline samples were selected for resistance analysis from all patients and from selected patients during treatment who exhibited viral breakthrough or who were nonresponsive to treatment during the first 42 days of dosing, as defined by the clinical protocol. Viral breakthrough was defined as a >1log10 increase from nadir HCV RNA at two consecutive HCV RNA measurements or plasma HCV RNA >100 IU/mL in two consecutive visits after becoming undetectable. A nonresponder was defined as a patient who experienced a ≤2log10 decrease in HCV RNA levels through day 28. Population sequences were aligned to either H77 Diflunisal (GenBank NC_004102) or Con1 (GenBank AJ238799) for genotypes 1a and 1b, respectively. For resistance analysis, eight

independent PCR reactions were attempted for each sample. Depending on the number of amplicons obtained, a maximum of four of these products were directly sequenced per time point (i.e., population sequencing). To determine host genetic determinants of response to Peg-IFN-α-2a/RBV or MK-7009 therapy, informed consent and blood samples for interleukin (IL)28B genetic analysis were requested from all study participants. Blood samples for genetic analysis were collected in an ethylene diamine tetraacetic acid tube at the study site. Samples were centrifuged, plasma was discarded, and cell pellets were stored frozen until DNA extraction and genotyping analysis. Subject samples were genotyped for IL28B rs12979860, rs12980275, and rs8103142 alleles at an outsourced vendor using vendor-proprietary DNA Sanger sequencing assays. This study was designed to randomize a total of 85 patients into five treatment groups.