Efficacy and safety of romiplostim N01 for second-line treatment of pediatric immune thrombocytopenia: A multicenter prospective observational study Free

Background: Pediatric immune thrombocytopenia (ITP) is an autoimmune disorder characterized by thrombocytopenia and an increased risk of bleeding. Current first-line therapies (e.g., corticosteroids, intravenous immunoglobulin) induce transient responses in most children, however, approximately 20-30% develop refractory or relapsed disease necessitating sequential interventions including thrombopoietin receptor agonists (TPO-RAs) as second-line options. Romiplostim N01 is a recombinant human thrombopoietin mimetic peptide-Fc fusion protein and has been approved in China as second-line therapy for adult ITP, but data in the pediatric population are limited. This study evaluates the efficacy and safety of romiplostim N01 in Children with refractory or relapsed ITP after first-line treatment.

Methods: In this prospective, multicenter observational study, we enrolled pediatric participants diagnosed with ITP (platelet count ≤ 30x10⁹/L), who showed no response to or experienced relapse after first-line therapy (corticosteroids and/or intravenous immunoglobulin) across four sites in Shandong Province, China. Romiplostim N01 was administered subcutaneously once a week, with rescue therapies (including corticosteroids and intravenous immunoglobulin) permitted at the investigator's discretion. The primary endpoint of this study is the rate of complete platelet response (CR: platelet count ≥ 100x10⁹/L without bleeding) at week 4. Secondary endpoints included the rate of partial response (PR, platelet count of 30-100x10⁹/L with at least a two-fold increase from baseline without bleeding) at the first week, the rate of durable response (CR/PR last at least 4 weeks), the rate of overall response (CR+PR) at the first week and during the entire treatment period, bleeding symptom resolution, and adverse events (AEs) graded by CTCAE version 5.0. This study was registered in Chinese Clinical Trial Registry (ChiCTR2400091685).

Results: Between January and June 2025, a total of 17 participants were enrolled, with one misdiagnosed ITP (later confirmed myelodysplastic syndrome) and one withdrawal, leaving 15 participants at data cutoff (July 30th , 2025). At baseline, participants median age was 7.0 (range: 5.0–14.0) years, 60.0% (9/15) was female, with a median baseline platelet count of 19.0 (range: 11.0-26.0)×10⁹/L. The median initial dose of romiplostim N01 was 5.0 (range: 4.0-5.8)µg/kg. Efficacy was analyzed in 13 participants who received at least 4 doses of romiplostim N01. At week 4, 61.5% (8/13) achieved CR. At the first week, 61.5% (8/13) achieved overall response, with 38.5% (5/13) achieved CR and 23.1% (3/13) achieved PR. Median time to response was 1.0 week. Durable response was achieved in 69.2% (9/13) participants, and 76.9% (10/13) achieved an overall response. Among patients with baseline bleeding, 100% (5/5) had complete resolution. AEs were reported in 20.0% (3/15), including thrombocytopenia (n=3) and upper respiratory tract infection (n=1). No grade ≥3 AEs or treatment discontinuations occurred.

Conclusion: Romiplostim N01 showed rapid efficacy in pediatric ITP, providing early and effective bleeding control with a well-tolerated safety. By facilitating rapid attainment of safer platelet thresholds, romiplostim N01 may mitigate bleeding risks during physical activities and improve overall quality of life. These findings support romiplostim N01 as a viable second-line option for children with refractory ITP. Further larger-scale studies with longer follow-up periods are needed to confirm long-term outcomes and optimize dosing strategies.