Efficacy and Safety of Oral E5501 Plus Standard of Care for the Treatment of Thrombocytopenia in Adults With Chronic Immune Thrombocytopenia (Amendment 02)

Inclusion Criteria

• Men and women greater than or equal to 18 years of age
• Participants diagnosed with cITP (greater than or equal to 12 months duration) according to the American Society for Hematology/British Committee for Standards in Hematology (ASH/BCSH) guidelines, and an average of 2 platelet counts greater than 30x10^9/L). The physical exam should not suggest any disease which may cause thrombocytopenia other than ITP
• Participants who previously received one or more ITP therapies (including, but not limited to corticosteroids, immunoglobulins, azathioprine, danazol, cyclophosphamide and/or rituximab).
• Participants must have had either initially responded (platelet count greater than 50x10^9/L) to a previous ITP therapy or have had a bone marrow examination consistent with ITP within 3 years to rule out myelodysplastic syndrome (MDS) or other causes of thrombocytopenia
• Prothrombin time/International Normalized Ratio (PT/INR) and activated partial thromboplastin time (aPTT) must have been within 80% to 120% of the normal range with no history of hypercoagulable state
• A complete blood count within the reference range (including white blood count [WBC] differential not indicative of a disorder other than ITP), with the following exceptions: hemoglobin: participants with hemoglobin levels between 10 g/dL (100 g/L) and the lower limit of normal (LLN) are eligible for inclusion, if anemia was clearly attributable to ITP (excessive blood loss); Absolute neutrophil count (ANC) greater than or equal to 1500/uL (1.5x10^9/L) (elevated WBC/ANC due to corticosteroid treatment is acceptable)

Exclusion Criteria

• Participants with known secondary immune thrombocytopenia (e.g., with known Helicobacter pylori-induced ITP participants infected with known human immunodeficiency virus [HIV] or hepatitis C virus [HCV] or participants with known systemic lupus erythematosus). (Revised per Amendment 01)
• Participants with significant medical conditions that may impact on the safety of the participant or interpretation of the study results (e.g., acute hepatitis, active chronic hepatitis; lymphoproliferative disease; myeloproliferative disorders, leukemia)
• History of MDS
• History of gastric atrophy (added per Amendment 01)
• History of pernicious anemia or participants with vitamin B12 deficiency (defined as less than LLN) who have not had pernicious anemia excluded as a cause (added per Amendment 01)
• Any prior history of arterial or venous thrombosis (stroke, transient ischemic attack, myocardial infarction, deep vein thrombosis or pulmonary embolism), and more than two of the following risk factors: hormone replacement therapy, estrogen-containing hormone replacement or contraceptive therapies, smoking, diabetes, hypercholesterolemia, medication for hypertension, cancer, hereditary thrombophilic disorders (e.g., Factor V Leiden, antithrombin III deficiency, etc.), or any other family history of arterial or venous thrombosis
• Participants with a history of significant cardiovascular disease (e.g., congestive heart failure [CHF] New York Heart Association Grade III/IV, arrhythmia known to increase the risk of thromboembolic events [e.g., atrial fibrillation], participants with a QT interval corrected for heart rate of >450 msec, angina, coronary artery stent placement, angioplasty, coronary artery bypass grafting)
• Participants with a history of cirrhosis, portal hypertension, and chronic active hepatitis
• Participants with concurrent malignant disease
• Use of immunoglobulins (IVIg and anti-D) within 1 week of randomization
• Splenectomy or use of rituximab within 12 weeks of randomization
• Use of romiplostim or eltrombopag within 4 weeks of randomization
• Participants who are currently treated with corticosteroids or azathioprine but have not been receiving a stable dose for at least 4 weeks prior to randomization or have not completed these therapies more than 4 weeks prior to randomization