Analysis of data from large clinical trials using either standard or peginterferon in combination with ribavirin have identified certain pretreatment host and viral factors as being predictive of achieving SVR. Using multivariate analysis, Manns et al (2001) identified HCV genotype, baseline viral load, age and absence of cirrhosis while Fried et al (2002) found HCV genotype, age and body weight to be predictive of SVR. Of these factors, HCV genotype is clearly the most dominant. Patients infected with HCV genotypes 2 or 3 achieve response rates nearly double those infected with genotype 1.
Other factors that appear to be important in predicting the outcome of therapy but that were not specifically identified in these two pivotal trials include race and the dose of ribavirin. Because very few African-Americans were included in the three pivotal trials described, race could not be separated out as an unfavorable predictive factor. However, other studies have confirmed the very low response rate among African-Americans, even using peginterferon and ribavirin.
Substantial research efforts are underway now to clarify the mechanisms responsible for low response rates in this ethnic group. For patients infected with HCV genotype 1, the dose of ribavirin administered appears to be critical. It has been suggested that the use of recombinant human erythropoietin may prevent ribavirin-associated anemia and allow larger doses of ribavirin to be given or minimize the need for dose reduction.
It has become apparent that the ultimate outcome of antiviral therapy may become apparent early on during treatment. In those patients destined to achieve end of treatment response, levels of HCV RNA fall rapidly and often become undetectable within the first few weeks of therapy.
In an analysis of data from two large pivotal trials using peginterferon and ribavirin, Davis (02) found that among 965 treated patients, 778 (80%) achieved an early virologic response (EVR, decrease by at least 2 log10 units or to undetectable HCV RNA in serum). Among 187 patients without an EVR, only 3 (1.6%) went on to have SVR. These findings suggest that the week 12 HCV RNA level can be used to assess the need to continue therapy, at least in those patients infected with HCV genotype 1. Generally, most clinicians treat genotype 2 or 3 patients for 24 weeks, without assessing EVR.