Two phase III studies of the protease inhibitor boceprevir in patients with chronic hepatitis C virus (HCV) genotype 1 infection have been completed and met their primary endpoints.

The HCV RESPOND-2 and HCV SPRINT-2 studies each evaluated two treatment strategies with boceprevir: 48 weeks of treatment for all patients (4-week lead-in with 1.5mcg/kg/week of peginterferon alfa-2b [Peg] and an investigational dose of 600-1400mg/day of ribavirin (riba) followed by the addition of boceprevir 800mg three times a day for 44 weeks), and response-guided therapy, in which patients with undetectable virus at week 8 and again at certain points later in the studies were able to stop all treatment at 36 weeks in HCV RESPOND-2 and at 28 weeks in HCV SPRINT-2. Patients who did not meet these criteria continued treatment with Peg/riba alone for a total treatment duration of 48 weeks. Control groups in the studies received Peg/riba at the doses described above plus placebo for 48 weeks.

The HCV RESPOND-2 study involved 403 previously treated patients and in the boceprevir 48-week treatment group, 66% of patients achieved sustained virologic response (SVR), and in the boceprevir response-guided therapy group, 59% of patients achieved SVR, compared to 21% of patients in the control group (p<0.0001 for both).

The HCV SPRINT-2 involved 1097 treatment-naïve patients who were enrolled in two separate cohorts, one with 938 non-African-American/Black patients and the other with 159 African-American/Black patients. In the study overall, 66% of patients in the boceprevir 48-week treatment group achieved SVR, and 63% of patients in the response-guided therapy group achieved SVR, compared to 38% of patients in the control group (p < 0.0001 for both).

Merck expects to complete regulatory submissions in the US and EU in 2010.