Romiplostim

What is it?

Immune thrombocytopenia destroys platelets faster than the marrow replaces them. Rather than suppress the immune attack, romiplostim pushes production: it activates the thrombopoietin receptor, the switch the body uses to make more platelets. It shares no sequence with thrombopoietin, which was deliberate after an earlier recombinant version caused antibodies that cross-reacted with the natural hormone.

The label covers adults with ITP who have not responded well enough to steroids, immunoglobulins or splenectomy, and children from one year with ITP for at least six months. Dosing starts at 1 mcg/kg weekly by subcutaneous injection and is adjusted to the platelet response. The aim is the lowest dose that keeps platelets at or above 50 × 10⁹/L to reduce bleeding, with weekly blood counts during adjustment; if platelets do not rise enough after four weeks at the 10 mcg/kg maximum, it is stopped. Peak levels come 7 to 50 hours after a dose, with half-lives from 1 to 34 days (median 3.5).

Its second indication is unusual: a single 10 mcg/kg dose for people acutely exposed to myelosuppressive doses of radiation, given as soon as possible after suspected or confirmed exposure.

The approval trials were placebo-controlled. Durable platelet responses occurred in 16 of 42 splenectomised and 25 of 41 non-splenectomised adults on romiplostim, against 0 of 21 and 1 of 21 on placebo. Against standard medical care in adults who had not had their spleen removed, platelet responses were 2.3 times as frequent, treatment failure was 11% against 30%, and splenectomy was needed by 9% against 36%. In children, durable responses were 52% against 10% on placebo, with 24% against 5% having serious adverse events.

Longer use and earlier chemotherapy data support those results. In 22 children with severe chronic ITP treated for a median of 167 weeks at a median 5.4 µg/kg a week, median platelet counts stayed above 50 × 10⁹/L after the first 12 weeks, and no one stopped because of adverse events. Before RECITE, a 2019 randomised trial in chemotherapy-induced low platelets corrected the count within three weeks in 14 of 15 patients on romiplostim against 1 of 8 observed without it, and 44 patients restarted chemotherapy on weekly romiplostim, only three having further reductions or delays.

Newer trials have widened its use. In the RECITE phase 3 trial in chemotherapy-induced low platelets, 84% on romiplostim against 36% on placebo needed no chemotherapy dose change for low platelets, with thromboembolic events in 2% against none. In aplastic anaemia refractory to immunosuppression, high weekly doses produced a haematological response in 84% at week 27 and a response in all three blood lines in 39% at a year.

The label's three warnings are a risk of myelodysplastic syndromes progressing to acute myeloid leukaemia, which is why it is not for low platelets caused by myelodysplasia; blood clots if platelets rise too high; and loss of response. It can be used with steroids, danazol, azathioprine, immunoglobulin and anti-D.

Mechanism of Action

Romiplostim is a peptibody: thrombopoietin-receptor-binding peptides fused to an antibody Fc fragment, which activates the receptor that drives platelet production.

Published Research

The studies behind romiplostim, read from their PubMed abstracts: ITP trials in adults and children, chemotherapy-induced low platelets and aplastic anaemia.

No studies of that type on this page.

Dosing Data

Nplate is a weekly injection under the skin, dosed by weight and adjusted to the platelet count.

Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.

Side Effects & Contraindications

Legal Status

Approved and in routine use.

Frequently Asked Questions

References

1. [fda-pi] Nplate (romiplostim) prescribing information, sections 1 and 2 (DailyMed SPL version 162, effective June 23, 2026; read October 1, 2026).
2. [pubmed] Kuter DJ, et al. "Efficacy of romiplostim in patients with chronic immune thrombocytopenic purpura: a double-blind randomised controlled trial." Lancet, 2008;371(9610):395-403. PMID: 18242413.
3. [pubmed] Kuter DJ, et al. "Romiplostim or standard of care in patients with immune thrombocytopenia." N Engl J Med, 2010;363(20):1889-99. PMID: 21067381.
4. [pubmed] Tarantino MD, et al. "Romiplostim in children with immune thrombocytopenia: a phase 3, randomised, double-blind, placebo-controlled study." Lancet, 2016;388(10039):45-54. PMID: 27103127.
5. [pubmed] Bussel JB, et al. "Long-term use of the thrombopoietin-mimetic romiplostim in children with severe chronic immune thrombocytopenia (ITP)." Pediatr Blood Cancer, 2015;62(2):208-213. PMID: 25345874.
6. [pubmed] Soff GA, et al. "Romiplostim Treatment of Chemotherapy-Induced Thrombocytopenia." J Clin Oncol, 2019;37(31):2892-2898. PMID: 31545663.
7. [pubmed] Al-Samkari H, et al. "Romiplostim versus Placebo for Chemotherapy-Induced Thrombocytopenia." N Engl J Med, 2026;394(11):1061-1073. PMID: 41812193.
8. [pubmed] Jang JH, et al. "Efficacy and safety of romiplostim in refractory aplastic anaemia: a Phase II/III, multicentre, open-label study." Br J Haematol, 2021;192(1):190-199. PMID: 33152120.
9. [pubmed] Mitani K, et al. "Long-term efficacy and safety of romiplostim in refractory aplastic anemia: follow-up of a phase 2/3 study." Blood Adv, 2024;8(6):1415-1419. PMID: 38134300.
10. [pubmed] Peffault de Latour R, et al. "Romiplostim in patients undergoing hematopoietic stem cell transplantation: results of a phase 1/2 multicenter trial." Blood, 2020;135(3):227-229. PMID: 31805185.