QL0911, a recombinant human thrombopoietin mimetic peptide-Fc fusion protein for injection, is a romiplostim (Nplate®) biosimilar for the treatment of primary immune thrombocytopenia (ITP). This phase III study aimed to assess the efficacy and safety of QL0911 in adult patients with primary chronic ITP.

This study consisted of a randomized, double-blind, placebo-controlled, 26-week treatment period, sequentially followed by an open-label, single-arm, 12-week treatment period, and an additional 4-week safety follow-up period.

Inclusion Criteria:

• Aged ≥18 years old;
• Diagnosed primary ITP for at least 12 months;
• Had received at least one first-line ITP treatment with no response or recurrence after treatment;
• Had a platelet count <30×10^9/L within 48 hours before the first dose;
• Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2;
• Fully understand and comply with the requirements of this study, and voluntarily sign the informed consent form.

Exclusion Criteria:

• Had a history of bone marrow stem cell abnormalities or myelodysplastic syndrome other than ITP-specific changes.
• Had arterial thrombosis, or venous thromboembolism; severe cardiovascular diseases; malignant tumors; secondary thrombocytopenia caused by autoimmune diseases.
• Underwent splenectomy within 12 weeks before the first dose;
• Had received ITP treatments (including rescue treatment) within 2 weeks before the first dose;
• Had received romiplostim (Nplate®) or eltrombopag (Revolade®), rhTPO or other agents that stimulate TPO receptors (also known as c-Mpl), and hematopoietic growth factors (HGFs) within 4 weeks before the first dose;
• Had received antineoplastic agents within 8 weeks before the first administration, but when treating ITP with hypomethylating agents (HMA) such as decitabine, a 4-week washout period was acceptable, as judged by the investigator;
• Had received antibody-based therapies within 14 weeks before the first dose; 8) had serum creatinine or total bilirubin >1.5 upper limit of normal (ULN), alanine transaminase (ALT) or aspartate transaminase (AST) >3 ULN, hemoglobin < 100g/L, absolute neutrophil count <1.5x10^9/L;
• Had prothrombin time (PT) or prothrombin time-international normalized ratio (PT-INR) or activated partial thromboplastin time (APTT) exceeded 20% of the reference range of normal values.