A Phase II Dose-escalation Study Characterizing the PK of Eltrombopag in Pediatric Patients With Previously Untreated or Relapsed Severe Aplastic Anemia or Recurrent Aplastic Anemia

Inclusion Criteria: For Cohort A patients: * History of prior diagnosis of SAA, * Diagnosis of relapsed/refractory SAA or recurrent AA following treatment for SAA, as per Section 5.1. Patients with recurrent AA (e.g., losing their response) are exempt from meeting the diagnostic criteria for SAA relapse at the time of study enrollment, but must have been previously diagnosed with SAA. * Agree to concurrent eltrombopag treatment with appropriate, investigator-selected Immunosuppressive therapy (IST) with either hATG + CsA or CsA. For Cohort B patients: * Diagnosis of SAA at time of enrollment. * Patients must not have been previously treated with IST, and must meet all criteria as described in Table 5-1. * Patients must agree to treatment with hATG + CsA concurrent with eltrombopag. All patients eligible for inclusion in this study must meet all of the following criteria: * Age 1 to \<18 years. * Assessments to rule out congenital/inherited bone marrow failure syndromes and other causes of immune-mediated pancytopenia, which may be treated with transplant, must be completed prior to enrollment. * Hematopoietic stem cell transplantation (HSCT) is not suitable or available as a treatment option or has been refused by the patient. (Candidacy for HSCT will be determined as per local practices or national guidelines.) * Bone marrow aspirate and biopsy at any time during the 4 weeks prior to first dose of eltrombopag. * Performance status score: Karnofsky ≥50 for patients 16 y…