Safety and Efficacy Study of Romiplostim (AMG 531) to Treat ITP in Pediatric Subjects

• Weeks With Platelet Count ≥ 50 x 10^9/L [ Time Frame: 12-week treatment period ] [ Designated as safety issue: No ]
  The number of weeks with platelet count ≥ 50 x 10^9/L during the 12 week treatment period.
• Bleeding Events (Grade 2 or Higher) [ Time Frame: 12-week treatment period (Weeks 2 - 13) ] [ Designated as safety issue: No ]
  Total number of bleeding events (Grade 2 or higher, i.e., mild to life-threatening, as defined in the protocol) for each participant during Weeks 2-13 (end-of-study visit for non-responders)
• Platelet Count ≥ 50 x 10^9/L for Two Consecutive Weeks [ Time Frame: 12-week treatment period ] [ Designated as safety issue: No ]
  Participant incidence of achieving a platelet count ≥50 x 10^9/L for two consecutive weeks during the 12 week treatment period.
• Increase in Platelet Count ≥ 20 x 10^9/L Above Baseline for Two Consecutive Weeks [ Time Frame: 12-week treatment period ] [ Designated as safety issue: No ]
  Participant incidence of achieving an increase in platelet count ≥20 x 10^9/L above baseline for two consecutive weeks during the 12 week treatment period.
• Requirement for Rescue Therapy (as Defined Per Protocol) [ Time Frame: 12-week treatment period ] [ Designated as safety issue: No ]
  Participant required rescue therapy (as defined per protocol) during the 12 week treatment period.

• pharmacokinetic exposure of AMG 531 as measured by drug concentrations taken at specified times during the study
• the number of weeks with platelet count >50 x 10^9/L during the 12 week treatment period
• the total number of bleeding events Grade 2 or higher for each subject during Weeks 2-13 (end-of-study visit for non-responders)
• the subject incidence of achieving a platelet count >50 x 10^9/L for two consecutive weeks during the 12 week treatment period
• the subject incidence of achieving an increase in platelet count >20 x 10^9/L above baseline for two consecutive weeks during the 12 week treatment period
• the subject incidence of requiring rescue therapy during the 12 week treatment period

The purpose of this study is to evaluate the safety and tolerability of romiplostim (AMG 531) in the treatment of thrombocytopenia in pediatric subjects with chronic ITP. We will also evaluate the efficacy of romiplostim (AMG 531) and characterize the pharmacokinetics of romiplostim (AMG 531). It is anticipated that romiplostim (AMG 531), when given at an effective dose and schedule, will be well tolerated treatment for thrombocytopenia among pediatric subjects with chronic ITP.

• Idiopathic Thrombocytopenic Purpura
• Thrombocytopenia in Pediatric Subjects With Immune (Idiopathic) Thrombocytopenic Purpura (ITP)
• Thrombocytopenia in Subjects With Immune (Idiopathic) Thrombocytopenic Purpura (ITP)

• Drug: Placebo
  Starting dose of 1.0 ug/kg. Dose adjustments are made throughout the study based on individual platelet counts.
• Drug: AMG 531
  Starting dose of 1.0 ug/kg. Dose adjustments are made throughout the study based on individual platelet counts.
  Other Name: romiplostim

• Placebo Comparator: II.
  5 thrombocytopenic (as defined per protocol) subjects
  Intervention: Drug: Placebo
• Experimental: I.
  15 thrombocytopenic (as defined per protocol) subjects
  Intervention: Drug: AMG 531

Inclusion Criteria:

• Before any study-specific procedure, the appropriate written informed consent must be obtained. In addition to the written informed consent, the assent of the child from those subjects capable of providing assent must also be obtained if requested by the IRB/IEC.
• Diagnosis of ITP according to The American Society of Hematology (ASH) Guidelines at least six months prior to screening
• Age ≥ 12 months and < 18 years at enrollment
• The mean of two platelet counts taken during the screening period must be ≤ 30 x 10^9/L with no single count >35 x 10^9/L
• A serum creatinine concentration ≤ 1.5 times the laboratory normal range (for each age category)
• Adequate liver function; serum bilirubin ≤ 1.5 times the laboratory normal range
• Hemoglobin >10.0 g/dL

Exclusion Criteria:

• Known history of a bone marrow stem cell disorder (any abnormal bone marrow findings other than those typical of ITP must be approved by Amgen before a subject may be enrolled in the study)
• Known history of venous or arterial thrombotic or thromboembolic event
• Known history of congenital thrombocytopenia
• Known history of malignancy except basal cell carcinoma
• Known history of hepatitis B, hepatitis C, or HIV
• Known history of systemic lupus erythematosus, Evans Syndrome, or autoimmune neutropenia
• Known positive lupus anticoagulant or history of antiphospholipid antibody syndrome
• Known history of Disseminated Intravascular Coagulation, Hemolytic Uremic Syndrome, or Thrombotic Thrombocytopenic Purpura
• Currently receiving any treatment for ITP except for corticosteroids
• IV Ig or anti-D Ig within two weeks prior to the screening visit
• Rituximab (for any indication) within 14 weeks before the screening visit or anticipated use during the time of the proposed study
• Splenectomy within eight weeks of the screening visit
• Received hematopoietic growth factors including IL-11 (oprelvekin) within four weeks before the screening visit
• Received any alkylating agents within eight weeks before the screening visit or anticipated use during the time of the proposed study
• Subject is currently enrolled in or has not yet completed at least four weeks since ending other investigational device or drug trial(s), or subject is receiving investigational agent(s)
• Past or present participation in any study evaluating PEG-rHuMGDF, recombinant human thrombopoietin (rHuTPO), AMG 531, or related platelet product
• Pregnant (i.e. positive urine pregnancy test) or breast feeding
• Subject is not using adequate contraceptive precautions, if applicable.
• Known hypersensitivity to any recombinant E coli-derived product
• Subject has any kind of disorder that compromises the ability to comply with all study procedures