High-Dose Dexamethasone Combined With Orelabrutinib Versus High-Dose Dexamethasone Combined With Placebo in Adult Patients With Newly Diagnosed Primary Immune Thrombocytopenia

1. Subjects must thoroughly understand the nature, significance, potential benefits, possible inconveniences, and potential risks of the trial prior to enrollment. They must understand the study procedures and voluntarily sign the informed consent form.
2. Male or female subjects aged 18-80 years (inclusive).
3. Body weight ≥35 kg at screening.
4. Adult patients with newly diagnosed, untreated primary ITP, with platelet count (PLT) \<30×10⁹/L and no active bleeding in vital organs.
5. Subjects who responded to prior treatment with oral dexamethasone 40 mg/day for 4 days, defined as meeting all three of the following criteria on any day between Day 5 and Day 7 post-treatment: ① PLT ≥30×10⁹/L; ② ≥2-fold increase from baseline; and ③ no active bleeding. Between Week 2 and Week 12, any abnormal PLT result meeting any of the following criteria must be confirmed by repeat testing at Qilu Hospital within 24-48 hours: ① PLT \<30×10⁹/L; ② \<2-fold increase from baseline; or ③ active bleeding.
6. Women of childbearing potential must use an effective method of contraception during the screening period, throughout the entire trial, and for 90 days following the last dose of study medication.

Exclusion Criteria:

1. Subjects with severe ITP at screening (e.g., life-threatening thrombocytopenia, major bleeding events, or requiring urgent treatment including intravenous immunoglobulin, high-dose glucocorticoids, or plasma exchange), whom the investigator anticipates will require rescue treatment within 2 weeks after enrollment.
2. Subjects with autoimmune systemic diseases other than ITP, unless the investigator determines that such conditions will not affect the evaluation of study outcomes.
3. Subjects who failed to respond to prior treatment with oral dexamethasone 40 mg/day for 4 days, defined as meeting any of the following criteria on any day between Day 5 and Day 7 post-treatment: ① PLT \<30×10⁹/L; ② \<2-fold increase from baseline; or ③ active bleeding.
4. History of intracranial hemorrhage within 6 months prior to screening.
5. Subjects with a history of coagulation disorders other than ITP, such as disseminated intravascular coagulation, hemolytic uremic syndrome, or thrombotic thrombocytopenic purpura.
6. Subjects with a known hypersensitivity to any component of the study drugs described in this protocol.
7. Known human immunodeficiency virus (HIV) infection, or positive serologic test results.
8. Subjects with positive tuberculosis screening test (based on interferon-gamma release assay, including T-SPOT®, etc.), or active, latent, or incompletely appropriately treated tuberculosis at screening.
9. Activated partial thromboplastin time (aPTT) ≥1.5× upper limit of normal (ULN) or international normalized ratio (INR) ≥1.5 at screening.
10. Organ dysfunction, with the following laboratory findings at screening: Absolute neutrophil count (ANC) \<1.5×10⁹/L; hemoglobin \<90 g/L; lymphocyte count \<0.8×10⁹/L. Total bilirubin >1.2×ULN; aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >ULN. Amylase or lipase >2×ULN. Estimated glomerular filtration rate (eGFR) \<40 mL/min/1.73 m² calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula. Immunoglobulin IgG \<6 g/L.
11. Pregnant or lactating women.
12. Subjects unable to undergo blood collection, or with contraindications to phlebotomy.
13. Any other condition that the investigator considers unsuitable for participation in this trial.