Schering-Plough Corporation announced plans to initiate a major clinical study involving 2,880 patients that for the first time will directly compare the two approved forms of pegylated interferon therapy for chronic hepatitis C virus (HCV) infection: PEG-Intron (peginterferon alfa-2b/Schering Corporation) versus Pegasys (peginterferon alfa-2a/Hoffmann-La Roche Inc), both used in combination with ribavirin. Schering-Plough Research Institute (SPRI), in collaboration with leading medical centers, will conduct the comparative study in response to requests by the hepatitis C medical and patient communities, and to clear up misperceptions in the marketplace about these two treatments.

The IDEAL trial (Individualized Dosing Efficacy vs. flat dosing to Assess optimaL pegylated interferon therapy) will compare the efficacy and safety of individualized weight-based dosing with PEG-Intron and Rebetol (ribavirin, USP) versus Pegasys, which is administered as a flat dose to all patients regardless of individual body weight, and Copegus (ribavirin, USP) dosed either at 1,000 mg or 1,200 mg, in U.S. patients with chronic hepatitis C, genotype 1. Genotype 1 virus is the most common worldwide, the most difficult to treat successfully and accounts for about 70 percent of HCV infection among Americans.

PEG-Intron is a form of interferon alfa-2b that has been chemically "pegylated" so it is retained in the body longer than standard interferon, thereby providing for once weekly administration. Pegasys is a pegylated form of interferon alfa-2a.

PEG-Intron and Rebetol combination therapy is the most-prescribed treatment for chronic hepatitis C worldwide, with more than 300,000 patients having received this treatment since its introduction in 2001.