Study of a New Medication for Childhood Chronic Immune Thrombocytopenia (ITP), a Blood Disorder of Low Platelet Counts That Can Lead to Bruising Easily, Bleeding Gums, and/or Bleeding Inside the Body.

Inclusion Criteria: * Written informed consent must be obtained from the patient's guardian and accompanying informed assent from the patient (for children over 6 years old) * Patients must be between 1 year and \<18 years of age at Day 1 * Patients will have a confirmed diagnosis of chronic ITP for at least 1 year, at screening, according to the guidelines published in the International Working Group Report * A peripheral blood smear or bone marrow examination will support the diagnosis of ITP with no evidence of other causes of thrombocytopenia. * Patients must be refractory or have relapsed after at least one prior ITP therapy, or patients must be unable, for a medical reason, to continue other ITP treatments. * Patients must have a Day 1 (or within 48 hours prior) platelet count \<30 Gi/L. * Previous therapy for ITP with immunoglobulins (IVIg and anti-D) must have been completed at least 2 weeks prior to Day 1, or these therapies must have been completed at least 1 week prior to Day 1 and have been clearly ineffective. * Previous treatment for ITP with splenectomy, rituximab and cyclophosphamide must have been completed at least 4 weeks prior to Day 1. * Patients treated with concomitant ITP medication (e.g. corticosteroids or azathioprine) must be receiving a dose that has been stable for at least 4 weeks prior to Day 1. * Patients must have a complete blood count (CBC) not suggestive of another hematological disorder. * Patients must have the following laboratory resul…