Hepatitis C virus (HCV) is estimated to infect 17 million individuals worldwide or roughly 3% of the worlds population. Over time chronic HCV infection can lead to liver cirrhosis or liver cancer. While the current combination therapy of interferon alpha and ribavirin  has proven beneficial in many patients, roughly 50% are either unresponsive or fail to achieve a sustained response. This is particularly true for HCV type 1b which is the predominant form of HCV in North America and Europe.

On May 13, 2011 the Food and Drug Administration, US approved Merck’s VICTRELIS™ (boceprevir), a hepatitis C virus (HCV) protease inhibitor. Victrelis will be used to treat HCV type 1b in combination with peginterferon alfa and ribavirin in adult patients (18 years and older) with compensated liver disease, including cirrhosis, and who were either previously untreated or who failed previous interferon and ribavirin therapy.

Victrelis in combination with peginterferon alfa and ribavirin has not been studied in patients documented to be historical null responders (less than a 2-log₁₀ HCV-RNA decline by treatment week 12) during prior therapy with peginterferon alfa and ribavirin. The clinical studies included subjects who were poorly interferon responsive. Subjects with less than 0.5-log₁₀ HCV-RNA decline in viral load at Treatment Week 4 with peginterferon alfa plus ribavirin alone are predicted to have a null response (less than 2-log₁₀ viral load decline at Treatment Week 12) to peginterferon alfa and ribavirin therapy. Poorly interferon responsive patients who were treated with VICTRELIS in combination with peginterferon alfa and ribavirin have a lower likelihood of achieving a sustained virologic response (SVR), and a higher rate of detection of resistance-associated substitutions upon treatment failure, compared to patients with a greater response to peginterferon alfa and ribavirin.