R

• Rapid Virologic Response (RVR): "Undetectable" HCV RNA level at week 4 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. Obtaining a RVR is associated with a high likelihood of treatment success. 
• Reactivation of hepatitis B: Reappearance of active necroinflammatory disease in the liver in an individual who was known to have resolved hepatitis B or inactive carrier state.
• Response-guided therapy (RGT): Response-guided therapy is a strategy of following early HCV viral kinetics and adjusting the treatment duration based on the early virologic response. Response-guided therapyhas been utilized with triple-therapy regimens that include an NS34A protease inhibitor.  This strategy contrasts with the traditional fixed-duration therapy, which has been the standard of care with peginterferon and ribavirin for genotype 1 HCV infection. 
• Ribavirin: Ribavirin is an antiviral medication used in combination with other agents to treat HCV infection. The ribavirin mechanism of action involves one or more of the following: (1) enhanced immune clearance of HCV via shifting from Th2 to Th1, (2) inhibition of the cellular enzyme Inosine Monophosphate Dehydrogenase (IMPDH), leading to depletion of cellular levels of GTP, which is a necessary substrate for HCV replication, (3)inhibition of the HCV NS5B RNA polymerase enzyme (RdRp), (4) generation of RNA mutagenesis, which results in the creation of defective HCV particles.