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• Early Virologic Response (EVR): A ≥2 log10 decline in hepatitis C (HCV) RNA level from baseline value by week 12 of treatment. A complete EVR is defined as decline to "undetectable" HCV RNA level by week 12; a partial EVR is detectable HCV RNA but ≥2 log10 decline. The definition of undetectable varies based on the sensitivity of the assay used (which can range from 10 to 50 IU/ml in lower limit of detection) and stringency required for a particular treatment regimen. A failure to achieve an EVR is associated with a high likelihood (>96%) of treatment failure.
• Encephalopathy: Describes a syndrome of global brain dysfunction characterized by confusion and cognitive impairment. Mild encephalopathy may cause only slight reductions in normal cognitive function whereas severe encephalopathy usually manifests a severe confusion and somnolence, and in extreme cases, coma. Hepatic encephalopathy refers to encephalopathy resulting from liver disease.
• End of Treatment Response (ETR): "Undetectable" HCV RNA (<50 IU/mL) at the end of treatment. An ETR does not accurately predict a sustained virologic response (SVR), but is necessary for an SVR to occur.  When evaluating ETR, undetectable HCV RNA is usually defined as HCV RNA <50 IU/mL.
• Extended Rapid Virologic Response (eRVR): "Undetectable" HCV RNA level at weeks 4 and 12 of treatment. The definition of undetectable varies based on the sensitivity of the assay used (which can range from 10 to 50 IU/ml in lower limit of detection) and stringency required for a particular treatment regimen.