Extended Dosing With Eltrombopag for Severe Aplastic Anemia

Background: \- Eltrombopag is a drug being tested for treating severe aplastic anemia. It can help improve blood counts in these patients. However, researchers do not know how long the drug can and should be taken for this type of anemia. Objectives: \- To look at whether 6 months of treatment with eltrombopag can improve patient s blood counts. Eligibility: \- Individuals at least 2 years of age who are taking eltrombopag for severe aplastic anemia. Design: * Participants will take eltrombopag by mouth once a day for 6 months. * Blood samples will be collected every 2 weeks for the first 6 months. Bone marrow samples will be collected at 3 and 6 months. These samples will look at the effects of the study drug on the marrow. * Participants will continue to take the study drug for as long as it is effective and if the side effects are not severe.