This study is a double-blind, randomized, placebo-controlled, parallel group, repeat-dose, study conducted in two parts (Part A and Part B) examining 30, 50, and 75 mg doses of SB-497115-GR as a treatment for patients with ITP who have failed prior therapy. The study is designed to determine the proportion of patients with a platelet count =50,000/µL after 42 days. In Part B, 99 newly-recruited subjects will be randomized to one of two dosing arms in a 2:1 ratio of active:placebo. During the 6 week study period, subjects will start on placebo or active drug (50 mg) and may have a dose increase to 75 mg based upon their platelet count at day 22.

A double-blind, randomized, placebo-controlled, parallel group study to investigate the efficacy, safety, tolerability, pharmacokinetics, and pharmacodynamics of SB-497119-GR, a thrombopoietin receptor agonist, administered at 30, 50, and 75 mg as oral tablets once-daily for 6 weeks to adult male and female subjects with refractory, chronic immune thrombocytopenia purpura

Inclusion criteria:

• Patients with chronic low platelet count (less than 30,000/µL) for 6 months who have failed at least one treatment for chronic low platelet count.
• Patients receiving chronic maintenance steroid therapy must have received a stable dose for at least 1 month.
• Normal PT and PTT.

Exclusion criteria:

• History of clotting disorder.
• Females who are pregnant or are receiving hormone replacement therapy or systemic contraceptives.
• History of alcohol/drug abuse or dependence within 1 year.
• Use of aspirin, aspirin-containing compounds, salicylates, antacids, rosuvastatin, pravastatin, non-steroidal anti-inflammatory drugs during the study and within 3 weeks prior to starting the study.
• History of HIV infection or active infection with Hepatitis B or C.