Previously untreated chronic hepatitis C patients undergoing therapy with peginterferon alfa and ribavirin have a very poor probability of achieving a sustained virologic response if they either do not have a 100-fold or greater reduction in their plasma HCV RNA levels at the 12th week of treatment or have detectable plasma HCV RNA at the 24th week of treatment. ISIS 14803 is an experimental antiviral medication for the treatment of chronic hepatitis C that has been given to chronic hepatitis C patients in two previous single-agent clinical trials (approximately 70 patients).

In this clinical research study, 12 weeks of ISIS 14803 treatment will be added to the peginterferon alfa and ribavirin treatment regimen of previously untreated chronic hepatitis C patients who have a very poor probability of achieving a sustained virologic response based upon either of the above two criteria. Enrolled patients must continue to be treated with peginterferon alfa and ribavirin and must begin ISIS 14803 treatment within four weeks of their HCV RNA result report date. ISIS 14803 will be given as a two-hour intravenous infusion, two times each week, for 12 weeks. Depending on their HCV response to the three-drug combination, patients may continue treatment with peginterferon alfa and ribavirin after the end of ISIS 14803 treatment. Patients will be monitored for at least eight weeks (for safety) after the end of ISIS 14803 treatment and possibly for longer (for sustained virologic response). Two dose levels of ISIS 14803 will be studied in this trial, 3 and 6 mg/kg ideal body weight.