Boceprevir (INN, trade name Victrelis) is a protease inhibitor used to treat hepatitis caused by hepatitis C virus (HCV) genotype 1. It binds to the HCV nonstructural protein 3 active site. It was initially developed by Schering-Plough, then by Merck after it acquired Schering in 2009. It was approved by the FDA in May 2011. In January 2015, Merck announced that they would be voluntarily withdrawing Victrelis from the market due to the overwhelming superiority of newer direct-acting antiviral agents, such as ledipasvir/sofosbuvir. Clinical trials SPRINT-1 trial The SPRINT-1 trial was a phase-II trial of boceprevir in difficult-to-treat patients with HCV genotype 1. Study results were announced at the 44th annual meeting of the European Association for the Study of the Liver in Copenhagen in April, 2009. When used in combination with peginterferon alfa-2b and ribavirin, boceprevir resulted in significantly higher sustained viral response (SVR) rates in the most difficult-to-treat patients with genotype 1. The phase-II trial compared three different regimens: four weeks of peginterferon alfa-2b (1.5 micrograms/kg once weekly) plus ribavirin (800 to 1400 mg daily based on patient weight) followed by boceprevir (800 mg three times a day in addition to peginterferon and ribavirin) for 24 weeks or 44 weeks; boceprevir in combination with peginterferon alfa-2b plus ribavirin as above for 28 or 48 weeks (triple therapy); and peginterferon alfa-2b plus low-dose ribavirin (400 to 1000 mg/day) and boceprevir for 48 weeks. The patients enrolled in the SPRINT-1 study were among the most difficult to treat, and were exclusively those with genotype 1. (The patients were all treatment naive.) Additionally, many of the patients had other difficult-to-treat indices, including cirrhosis (6–9%), high viral load (90%), and African-American ancestry (14–17%). An SVR after 24 weeks off therapy of 75% was achieved in the group treated for 48 weeks with four weeks of lead-in therapy with peginterferon alfa-2b plus ribavirin followed by the addition of boceprevir. This represents a near doubling of the rate of SVR compared to standard therapy without boceprevir in this group. Anemia was the most common adverse event. It occurred in half of the patients who received boceprevir and by about a third of the patients taking peginterferon alfa-2b plus ribavirin at the standard dose. The lead investigator of the study was Dr. Paul Kwo, associate professor of medicine at the School of Medicine, Indiana University, in Indianapolis, Indiana, USA. SPRINT-2 trial The SPRINT-2 trial was