Treatment Response: Response to hepatitis C treatment is measured by change in HCV viral load at different time points. Since it is a common practice to release interim data from HCV treatment trials, it is important to understand what these terms mean, so that interim results can be properly interpreted. It is important to consider the threshold of detection of the test used to measure HCV viral load, since these thresholds vary widely. The most sensitive tests can detect >5 copies IU/mL.
RVR (Rapid Virological Response): RVR means that there is no detectable hepatitis C virus in the blood after 4 weeks of treatment. An RVR is a good indication of SVR, but it is not as accurate for predicting who is unlikely to have SVR. Therefore, HCV treatment should not be discontinued if there is no RVR. RVR is mainly used in research.
EVR (Early Virological Response): EVR means that hepatitis C viral load has dropped by 99% (2 logs), or is undetectable after 12 weeks of HCV treatment. An EVR is a good predictor of the ultimate response to HCV treatment. If a person does not have an EVR, their chance of SVR is very low (1-4%). Usually, HCV treatment is discontinued in people who do not have an EVR.
ETR (End-of-Treatment Response): ETR means that there is no detectable hepatitis C virus in the blood at completion of HCV treatment. The ETR is usually higher than the SVR rate, because the hepatitis C virus may reappear in a persons blood after completion of HCV treatment.
SVR (Sustained Virological Response): SVR means that there is no hepatitis C virus detectable in the blood six months after a person completes HCV treatment. Many experts regard SVR as a cure, and it is an indication of long-term remission. SVR rates are always lower than response rates from earlier time points.
SVR-12: SVR-12 means that there is no hepatitis C virus detectable in the blood 12 weeks after completion of HCV treatment. Although it has not been prospectively validated, many experts agree that relapse (meaning the emergence of detectable hepatitis C virus in blood after completion of treatment) is most likely to occur within 12 weeks. However, FDA and other regulatory agencies require 24 weeks of post-treatment follow-up before a person is considered to have achieved an SVR.
HCV Treatment History: There is a growing population of people who did not have a sustained virological response from HCV treatment. They are sometimes referred to as "treatment failures," but the term "treatment-experienced" is preferable, although both are not sufficiently specific.
It is important to know how treatment-experienced people responded to their first course of treatment, and the regimen that they were treated with, because these factors help to predict the likelihood of SVR from re-treatment. People initially treated with standard interferon, or standard interferon plus ribavirin, may achieve SVR when re-treated with pegylated interferon and ribavirin. Sometimes, HCV re-treatment trials study a mixed population of relapsers, partial responders, non-responders, and null responders, which makes it difficult to interpret the results.
Null Responder: A null responder is someone who achieves little or no decrease in hepatitis C viral load during HCV treatment. Null responders are highly unlikely to respond to re-treatment with an interferon-based regimen.
Non-responder: Often referred to as a "treatment failure," a non-responder is someone who does not have an EVR or, if they stay on treatment for 24 weeks, does not ever have a 2-log (99%) drop in hepatitis C viral load or undetectable HCV RNA during hepatitis C treatment.
Partial Responder: A partial responder is someone who experiences at least a 2-log decrease in hepatitis C viral load during HCV treatment. Partial responders are more likely to respond to re-treatment than non-responders or null responders.
Relapser: The term relapser refers to someone who has had an EVR or ETR, but whose virus rebounded after they completed HCV treatment. People who had a relapse after completing HCV treatment are more likely to achieve SVR after re-treatment than partial responders, non-responders, or null responders.
About clinical trials:
www.clinicaltrials.gov (accessed on March 4, 2008).
About HCV drug development and research:
HCV Advocate (www.hcvadvocate.org) offers conference reporting and an up-to-date HCV pipeline chart, available on-line at: http://www.hcvadvocate.org/hepatitis/hepC/ HCVDrugs.html (accessed on March 4, 2008).
HIV and Hepatitis.com offers news and conference reports: www.hivandhepatitis.com (accessed on March 4, 2008).
NATAP (National AIDS Treatment Advocacy Project) offers comprehensive information on HCV research and drug development: www.natap.org (accessed on March 4, 2008).