Biosimilar Romiplostim Shows Equivalence to Reference Product for Chronic ITP

The romiplostim biosimilar GP40141 showed equivalent efficacy and was a comparable option to reference romiplostim (Nplate; Amgen) in immune thrombocytopenia (ITP), a rare autoimmune disorder.1 New data published in the journal EJHaem confirmed its efficacy and safety, with adverse events (AEs) similar between groups in the study.

The multicenter, single-blind, randomized controlled trial (NCT06497036) evaluated the biosimilar’s performance in adult patients with persistent or chronic ITP. The results showed the biosimilar romiplostim to be analytically and clinically comparable to its reference drug, a significant finding for both patients and health care systems grappling with rising drug costs.

Immune thrombocytopenia is characterized by the destruction of platelets, which can lead to increased bleeding risks and a reduced quality of life.2 The condition affects approximately 2.9 to 6.4 people per 100,000 adults annually.1 For many, ITP becomes a chronic, lifelong condition requiring sustained management.

Thrombopoietin receptor agonists such as romiplostim have become a cornerstone of ITP treatment by stimulating platelet production. Although effective, the high cost of these therapies, particularly the injectable romiplostim, has been a major barrier to widespread adoption, especially in resource-constrained regions.

“The development of biosimilar romiplostim aims to enhance the accessibility and affordability of this critical therapy, providing a lower-cost alternative that can reduce the financial burden on healthcare systems and improve patient access to essential medications,” the authors wrote.

Early in vitro studies confirmed GP40141’s comparability across 23 quality parameters, the authors explained. Preclinical trials in both rats and cynomolgus monkeys further demonstrated similar pharmacokinetics and pharmacodynamics, reinforcing the biosimilar's profile. A subsequent Phase 1 trial in healthy volunteers also validated its similarity to the reference product.

The phase 3 trial, which is the focus of the new report, confirmed these earlier findings in a population of 136 adults with ITP. The study, funded by GP40141 developer Geropharm, randomized patients 1:1 to receive either GP40141 or reference romiplostim for 26 weeks. The main end point in the trial was the proportion of patients achieving a platelet response (≥ 50 × 109/L) at week 11.

In the test group, 78% of patients showed platelet response after 10 weeks, compared with 85% in the comparison group. Between groups, the absolute difference in proportion was −0.06 (95% CI, −0.196 to 0.068), which falls within equivalence limits (−0.225 to 0.225). There were no significant differences in durable response rates, bleeding events, or safety profiles between the biosimilar and reference drug groups.

There were a total of 46 AEs in 22 patients reported during the study period in the test group vs 38 AEs affecting 18 patients in the reference drug group. The number of AEs and proportion of patients who experienced AEs did not significantly differ between the groups. The most frequent AE was petechiae, with mucosal bleeding also common. Most cases were mild, the authors noted.

The authors concluded that the biosimilar is not only effective but also safe, with no clinically meaningful differences in terms of quality, biological activity, or efficacy when compared with the reference drug.

The study had several limitations, including an incomparably low number of AEs compared with pivotal studies of romiplostim and its biosimilar. Underreporting cannot be ruled out, the authors explained. The single-blinded nature of the study was another limitation.

“Although the study was single-blinded, all efficacy end points were assessed using objective measures, therefore, the results can be considered reliable,” the authors wrote. “… Our aim was to provide evidence that treatment with biosimilar has equal efficacy and comparable safety, because the safety profile of romiplostim was already described elsewhere.”

References

1. Melikyan AL, Protsenko EA, Salogub GN, et al. Multicenter single-blind randomized controlled trial of the romiplostim biosimilar. EJHaem. 2025;6(4):e70105. doi:10.1002/jha2.70105

2. Pietras NM, Gupta N, Justiz Vaillant AA, et al. Immune thrombocytopenia. StatPearls [Internet]. Updated May 5, 2024. Accessed August 22, 2025. https://www.ncbi.nlm.nih.gov/books/NBK562282/