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

Inclusion Criteria: 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 Exclusion Criteria: 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