A Study of TQB3473 Tablets Compared to Placebo in the Treatment of Adult Primary Immune Thrombocytopenia

Inclusion Criteria: * Subjects voluntarily join this study, sign the informed consent form (ICF), and demonstrate good compliance; * Male or female subjects aged 18 to 75 years (calculated based on the date of signing the informed consent form); * Eastern Cooperative Oncology Group (ECOG) score of 0-1; * Diagnosis of primary ITP prior to randomization, with a duration of ≥12 months; * An average of at least three independent platelet counts (spaced more than 3 days apart) within the 3 months prior to randomization \<30×10\^9/L, with no count \>35×10\^9/L; and no severe bleeding within 4 weeks prior to screening; * Previous treatment with glucocorticoids and at least one standard ITP therapy that was ineffective or resulted in relapse. * Female subjects of childbearing potential must agree to use effective contraception during the study and for 6 months after the end of study treatment, with a negative serum or urine pregnancy test within 7 days prior to study enrollment; male subjects must agree to use effective contraception during the study and for 6 months after the end of study treatment, as detailed in Section 5.5. Exclusion Criteria: * Evidence of secondary causes of ITP (e.g., untreated Helicobacter pylori infection, leukemia, lymphoma, history of autoimmune diseases such as systemic lupus erythematosus, Hashimoto's thyroiditis, etc.) or drug-induced causes (e.g., anticonvulsants, antibiotics, heparin, etc.), or immune-mediated cytopenia involving two or more cell lines such as Evans syndrome or immune-related cytopenia; * Subjects with a history or current diagnosis of myelofibrosis, myelodysplastic syndrome, aplastic anemia, lymphoproliferative disorders, or other malignant hematologic diseases; * History of or concurrent other malignancies within the past 3 years. Exceptions include: other malignancies treated with a single surgical procedure and achieving continuous 5-year disease-free survival (DFS); cured cervical carcinoma in situ, non-melanoma skin cancer, and superficial bladder tumors \[Ta (non-invasive tumor), Tis (carcinoma in situ), and T1 (tumor invading the basement membrane)\]; * Conditions affecting venous blood sampling or multiple factors affecting oral medication (e.g., inability to swallow, chronic diarrhea, intestinal obstruction, etc.); * Adverse reactions from previous treatments have not resolved to ≤CTCAE grade 1, except for non-clinically significant and asymptomatic laboratory abnormalities judged by the investigator to pose no safety risks; * Previous bone marrow/hematopoietic stem cell transplantation or major solid organ transplantation; * Vaccination within 8 weeks prior to randomization or planned vaccination during the study period; * Major surgical treatment or significant traumatic injury within 4 weeks prior to randomization, or anticipated need for major elective surgery during the study treatment period (major surgery is defined as level 3 or higher according to the National Surgical Classification Catalog 2022); * History of intracranial hemorrhage or other severe bleeding in vital organs (≥CTCAE grade 3), or symptomatic gastrointestinal bleeding (e.g., hematemesis, melena, etc., excluding asymptomatic "occult blood test positive" and hemorrhoids) within 6 months prior to screening; * Arterial/venous thrombotic events within 12 months prior to randomization, such as cerebrovascular accidents (including transient ischemic attacks), deep vein thrombosis, or pulmonary embolism; * ITP-related symptoms and treatments: 1. Receipt of immunoglobulins or platelet transfusions within 2 weeks prior to randomization; 2. Receipt of treatments aimed at increasing platelet counts (including but not limited to glucocorticoids, Thyroid peroxidase (TPO), Thrombopoietin receptor agonists (TPO-RAs), cyclosporine, herbal medicines, etc.) within 4 weeks prior to randomization, except for those meeting inclusion criterion (8); 3. Use of rituximab or other anti-cluster of differentiation 20 (CD20) drugs within 14 weeks prior to randomization; 4. Splenectomy within 12 weeks prior to randomization. * Need for long-term/continuous use of medications affecting platelet function \[including but not limited to aspirin, clopidogrel, ticagrelor, non-steroidal anti-inflammatory drugs (NSAIDs), etc.\] or anticoagulant therapy; * Known allergy to the active ingredient or excipients of the investigational drug; * Previous treatment with Syk inhibitors; * Participation in another clinical trial and use of investigational drugs within 4 weeks prior to randomization; * Any condition judged by the investigator to pose a significant risk to the subject's safety or to affect the subject's ability to complete the study.