To evaluate the safety and efficacy of avatrombopag in the treatment of pediatric primary immune thrombocytopenia in patients who have been treated with eltrombopag before and switched to avatrobopag because of poor efficacy, excessive platelet fluctuation or intolerance, or patient preference, economic reasons, and other reasons.

Immune thrombocytopenia (ITP) is an organ-specific autoimmune disease, which is characterized by decreased platelet count and skin and mucosal bleeding. ITP is a kind of disease with increased platelet destruction and impaired platelet production caused by autoimmunity. Conventional treatment of adult ITP includes first-line glucocorticoid and immunoglobulin therapy, second line TPO and TPO receptor agonist, splenectomy and other immunosuppressive treatments (such as rituximab, vincristine, azathioprine, etc.).

Eltrombopag is currently the only TPO receptor agonist with indications for pediatric immune thrombocytopenia. However, at present, the treatment response of pediatric ITP is not good, and a considerable number of patients need to switched to other TPO receptor agonist, such as avatrombopag, because of poor efficacy, excessive platelet fluctuation or intolerance, or patient preference, economic reasons, and other reasons.

Therefore, the investigators designed this clinical trial to evaluate the efficacy and safety of avatrombopag in the treatment of pediatric immune thrombocytopenia in patients who who have been treated with eltrombopag before and switched to avatrobopag because of different reasons.

Inclusion Criteria:

• Age 6-18 years old (including both ends), male and female;
• Diagnosed with primary immune thrombocytopenia (ITP);
• Patients who had previously received eltrombopag treatment and then converted to avatrombopag treatment because of ineffectiveness (platelet count < 30×10^9/L after eltrombopag treatment, or platelet count increased less than 2 times of the basic value, or bleeding) or large platelet fluctuation or due to patient preference, economic reasons and other reasons;
• Cardiac function of the New York Society of Cardiac Function ≤ 2;
• Understand the study procedure and voluntarily sign the informed consent.

Exclusion Criteria:

• Secondary thrombocytopenia caused by various reasons, such as connective tissue disorders, bone marrow hematopoietic failure disease, myelodysplastic syndrome, malignancy, drugs, inherited thrombocytopenia, common variable immune deficiency, lymphoma, etc.;
• Subjects with primary disease of important organs (liver, kidney, heart, etc.), or with immune system diseases;
• Subjects who are known to be allergic to avatrombopag or any of its excipients;
• Subjects who had used rituximab within the last 3 months;
• Subjects who underwent splenectomy within the last 3 months；
• Subjects with a history of abnormal platelet aggregation that may affect the reliability of platelet count measurements；
• Any medical history or condition that the investigator deems unsuitable for participation in the study.