Randomized trial of valopicitabine (NM283) alone or with PEG-interferon vs. retreatment with PEG-interferon plus ribavirin (PEGIFN/RBV) in hepatitis C patients with previous non-response to PEGIFN.RBV: first interim results - O'Brien,C.; Godofsky,E.; Roriguez-Torres,M. (Hepatology, 2005)