A drug used to treat patients with immune thrombocytopenic purpura (ITP) who do not get better with other forms of treatment. In ITP, platelets (cells that cause blood clots to form) are destroyed by the immune system. Nplate is being studied as a way to treat low platelet counts caused by chemotherapy. It binds to the thrombopoietin receptor and causes the bone marrow to make more platelets. Nplate is also being studied in the treatment of myelodysplastic syndromes (a group of diseases in which the bone marrow does not make enough healthy blood cells). It is a type of thrombopoietin agonist. Also called AMG 531 and romiplostim.