SB497115 is an oral agent which activates the thrombopoietin receptor and increases platelet counts in healthy volunteers. This study is examining several different doses of SB497115 as a treatment for patients with chronic hepatitis C-related thrombocytopenia who are potential candidates for antiviral treatment with pegylated interferon and ribavirin. The study will be conducted in two phases, Parts 1 and 2. In Part 1, study subjects will be randomized to 4 weeks of SB-497115-GR or placebo administered daily without antiviral therapy. Subjects who successfully complete Part 1 (platelet count 70,000/µL for Pegasys and platelet count 100,000/µL for PEG-Intron) will then proceed to Part 2. In Part 2, subjects will receive an additional 8 weeks of SB-497115-GR or placebo administered daily with antiviral therapy.

A Double-Blind, Randomized, Placebo-Controlled, Multi-Centre, Dose-Ranging, Parallel Group, Phase II Study to Assess Efficacy, Safety/Tolerability, and Pharmacokinetics of a Thrombopoietin Receptor Agonist, SB-497115-GR, when Administered as 30, 50, and 75 mg Once Daily for 12 weeks in Subjects with Chronic Hepatitis C-Related Thrombocytopenia who are Potential Candidates for Antiviral Treatment with Pegylated Interferon and Ribavirin.

Inclusion criteria:

• Chronic low platelet count between 20,000 and <70,000/µL.
• Prior liver biopsy indicating chronic hepatitis within the previous 5 years or radiographic evidence of cirrhosis and / or endoscopic evidence of non-bleeding esophageal or gastric varices.

Exclusion criteria:

• History of heart attack or abnormal heart function.
• History of thrombosis within 1 year.
• History of alcohol or drug abuse or dependence within 1 year.
• Use of aspirin, aspirin-containing compounds, salicylates, antacids.
• History of HIV infection or active infection with Hepatitis B or C.
• Females who are pregnant.
• Patients using non-steroidal anti-inflammatory drugs during the study and within 3 weeks prior to starting the study.