Summary

Romiplostim (brand name Nplate) is a peptide-antibody fusion molecule (peptibody) that acts as a thrombopoietin (TPO) receptor agonist, stimulating platelet production in the bone marrow. FDA-approved since 2008 for adults with chronic immune thrombocytopenia (ITP) and later for paediatric ITP and acute radiation syndrome. As a peptibody, romiplostim combines a biologically active peptide sequence with an Fc domain to extend half-life, representing an innovative class of peptide therapeutics. For research and educational purposes only.

Mechanism

Romiplostim is a TPO receptor (c-Mpl) agonist peptibody. Its peptide binding domain activates c-Mpl on megakaryocyte progenitor cells, stimulating proliferation, differentiation, and platelet production. The Fc fusion domain enables FcRn-mediated recycling, giving a half-life of ~120-160 hours for weekly dosing. The peptide shares no sequence homology with endogenous TPO, avoiding cross-reactive neutralising antibodies.

Evidence base

Strong evidence — Two pivotal Phase 3 RCTs in adult chronic ITP demonstrated durable platelet responses of 38% (splenectomised) and 61% (non-splenectomised) vs. 0% and 5% for placebo. Long-term extension data show sustained efficacy over years. Paediatric Phase 3 trial confirmed 44% durable response. FDA-approved since 2008.

Key trials:

  • Kuter et al., Lancet 2008;371(9610):395-403
  • Bussel et al., NEJM 2006;355(16):1672-1681
  • Grainger et al., Lancet Haematol 2019;6(4):e218-e228

Protocols

Initial dose: 1 mcg/kg SC once weekly. Titration: Increase by 1 mcg/kg/week to achieve platelet count ≥50 × 10⁹/L. Max: 10 mcg/kg/week. Reduction: Reduce by 1 mcg/kg if >200 × 10⁹/L; withhold if >400 × 10⁹/L. Monitoring: Weekly CBC during titration; monthly once stable.

Research use only — not medical advice.

UK Status: POM (Prescription-Only Medicine)

Romiplostim is MHRA-licensed (Nplate) for adult and paediatric chronic ITP. It is not a controlled substance under the Misuse of Drugs Act 1971. Research institutions may source non-clinical material for in vitro or animal research under appropriate licensing.

Vendor notes

Romiplostim is a licensed pharmaceutical, not typically available from research peptide vendors. Source through NHS pharmacy or pharmaceutical supply chains. For non-clinical research, use certified chemical suppliers with COAs.

References

  1. Bussel JB, Kuter DJ, Pullarkat V, et al. Romiplostim, a Novel Thrombopoiesis-Stimulating Protein, for the Treatment of Immune Thrombocytopenia. N Engl J Med. 2006;355(16):1672-1681.
  2. Kuter DJ, Bussel JB, Lyons RM, et al. Efficacy of Romiplostim in Patients with Chronic Immune Thrombocytopenic Purpura: A Double-Blind Randomised Controlled Trial. Lancet. 2008;371(9610):395-403.
  3. Bussel JB, Provan D, Shamsi T, et al. Effect of Eltrombopag on Platelet Counts and Bleeding During Treatment of Chronic ITP: A Randomised Trial. Lancet. 2009;373(9664):641-648.
  4. Grainger JD, Locatelli F, Chotsampancharoen T, et al. Romiplostim in Children with Immune Thrombocytopenia: A Phase 3, Randomised, Double-Blind, Placebo-Controlled Study. Lancet Haematol. 2019;6(4):e218-e228.