Evaluating the Safety and Efficacy of Romiplostim (AMG 531) in Thrombocytopenic Subjects with Immune Thrombocytopenic Purpura (ITP)

- Diagnosis of ITP according to American Society of Hematology (ASH) guidelines at least 3 months before enrollment - Have completed at least 1 prior treatment for ITP - Two (including day -2) of the 3 platelet counts taken during the screening and pre-treatment periods must have fulfilled the following: -- less than 30 x 10^9/L for those subjects not receiving any ITP therapy, -- less than 50 x 10^9/L for those subjects receiving any ITP therapy - Eastern Cooperative Oncology Group performance status of 0 to 2 - Serum creatinine concentration ≤ 2 mg/dL (≤ 176.8 µmol/L) - Adequate liver function, as evidenced by a serum bilirubin ≤ 1.5 times the laboratory normal range - Hemoglobin greater than 10.0 g/dL - Written informed consent

- Considered a substantial risk for adverse outcomes because of a clinically important trend (as determined by the investigator) detected in the platelet counts during the screening period - Any known history of bone marrow stem cell disorder - Any active malignancy. If prior history of cancer other than basal cell carcinoma or cervical carcinoma in situ, no treatment or active disease within 5 years before randomization - Documented diagnosis of arterial thrombosis (ie, stroke, transient ischemic attack, or myocardial infarction) in the previous year; history of venous thrombosis (ie, deep vein thrombosis, pulmonary embolism) and receiving anticoagulation therapy - Unstable or uncontrolled disease or condition related to or impacting cardiac function (e.g., unstable angina, congestive heart failure [New York Heart Association (NYHA) greater than class II], uncontrolled hypertension [diastolic greater than 100 mmHg] or cardiac arrhythmia) - Have 3 or more of the following predisposing factors for thromboembolic events: diabetes; smoker using oral contraceptives; hypercholesteremia (> 240 mg/dL); treatment for hypertension - Known positive test for human immunodeficiency virus (HIV) infection or hepatitis C virus - Received any treatment for ITP (except for a constant dose schedule of corticosteroids) within 4 weeks before the screening visit - Received intravenous (IV) immunoglobulin (Ig) or WinRho within 2 weeks before the screening visit - Received hematopoietic growth factors, including interleukin (IL)-11 (Neumega®) within 4 weeks before the screening visit - Past or present participation in any study evaluating polyethylene glycol recombinant human magakaryopoiesis differentiating factor (PEG-rHuMGDF), recombinant human thrombopoietin (rHuTPO), or related platelet product - Received any alkylating agents within 8 weeks before the screening visit or anticipated use during the time of the proposed study - Received any monoclonal antibody (eg, rituximab) within 16 weeks before the screening visit or anticipated use during the time of the proposed study - Less than 4 weeks since receipt of any therapeutic drug or device that is not FDA approved for any indication before the screening period - Less than 2 months since major surgery (including laparoscopic splenectomy) - Pregnant or breast feeding - Subjects of reproductive potential who are not using adequate contraceptive precautions, in the judgment of the investigator