Efficacy and Safety of Romiplostim in Adult Subjects With Persistent or Chronic Immune Thrombocytopenia (ITP)

Inclusion Criteria: * Diagnosed with immune thrombocytopenia (ITP) for at least 6 months prior to signing the informed consent form (ICF). * Subject is ≥ 18 years old while signing the ICF. * Patients who have no response or relapsed after splenectomy. Or patients who have not been splenectomised and have no response or relapse to at least 1 prior treatment for immune thrombocytopenia (ITP). * The mean of 3 scheduled platelet counts taken during the screening period must be: \< 30 ×10\^9/L, with none \>35×10\^9/L. Exclusion Criteria: * Any known history of bone marrow stem cell disorder. Any abnormal bone marrow findings other than those typical of ITP. * Any active malignancy. If prior history of cancer other than basal cell carcinoma or cervical carcinoma in situ, and no treatment or active disease within 5 years prior to signing the ICF.. * Received hematopoietic growth factors (e.g., granulocyte colony-stimulating factor, macrophage colony-stimulating factor, erythropoietin, interleukin-11) for any reason within 4 weeks prior to signing the ICF. * Received myeloproliferative leukemia (MPL) stimulation product other than the subject who had suspended recombinant human thrombopoietin (rHuTPO) for injection for 4 weeks before signing ICF. * Received any anti-malignancy agents (e.g., cyclophosphamide, 6-mercaptopurine, vincristine, vinblastine, Interferon-alfa) for any reason within 8 weeks prior to signing the ICF. * Received any monoclonal antibody drugs (e.g., rituximab) for any reason within 14 weeks prior to signing the ICF. * Less than 4 weeks since end of any clinical trials about therapeutic drug or device prior to signing the ICF. * Pregnant or breastfeeding. * In the opinions of the principal investigator or investigators, the patients are not suitable for participation in this trial.