Romiplostim (Nplate)_Dosage, benefits & legal status
Also known as Nplate, Romiplate, AMG 531, Stimplate
A protein drug that carries four copies of a 14-residue peptide to switch on the receptor for thrombopoietin, the hormone that makes platelets. FDA-approved for immune thrombocytopenia since August 22, 2008.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Romiplostim (Nplate)?
Plain language first. The technical label stays, but it never stands alone.Overview
In immune thrombocytopenia (ITP) the immune system destroys platelets, and very low counts raise the risk of bleeding. In two 24-week placebo-controlled trials in adults, a platelet response came in 79% of those who had had their spleen removed and 88% of those who had not, against 0% and 14% on placebo, and grade 2 or worse bleeding was 15% against 34%. The dose is set by weekly blood counts, and the label warns of blood clots and of loss of response; fibers building up in the bone marrow have also been seen.
Romiplostim is a peptide-Fc fusion protein (a peptibody) of about 59 kDa, not a short peptide: each of its two identical 269-residue chains is a human IgG1 Fc fragment carrying, at its C-terminus, two copies of the 14-residue thrombopoietin receptor-binding peptide IEGPTLRQWLAARA joined by glycine linkers, four copies per molecule. It activates the thrombopoietin receptor (c-Mpl) on megakaryocytes and their precursors although it shares no sequence with natural thrombopoietin; Amgen makes it in E. coli. Part of its clearance runs through the same receptors on platelets, so blood levels fall as platelet counts rise.
What it's used for
A weekly injection under the skin, given by a health professional, to raise platelet counts in adults and children 1 year and older with immune thrombocytopenia who have not responded well enough to other treatment. It is also approved as a single dose after dangerous radiation exposure.
How does Romiplostim (Nplate) work?
What it does in the body, and where.Romiplostim switches on the receptor that thrombopoietin, the body's platelet hormone, uses, even though it looks nothing like that hormone.
- 01The binding peptideThe 14-residue peptide IEGPTLRQWLAARA was found in 1997 by screening peptide libraries and binds the thrombopoietin receptor with an affinity of about 2 nanomolar. On its own it is weak, but a linked pair was about 4,000 times more potent and roughly matched natural thrombopoietin, a 332-residue protein, in cell tests.
- 02
- 03More platelets, less drugSwitching on the receptor on megakaryocyte precursors in the bone marrow makes more of them mature and shed platelets; after one dose, counts peak in 2 to 3 weeks at 1.3 to 14.9 times baseline. Platelets carry the receptor too and soak up the drug, so levels fall as counts rise, and the dose is set by the platelet count.
What else is it used for?
Each group carries its own evidence level.Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
Adults, against placebo
FDA-approved- Human trial63 adults without a spleen: durable response 38% against 0%, any response 79% against 0%, rescue treatment 26% against 57%.
- Human trial62 adults with a spleen: durable response 61% against 5%, any response 88% against 14%; mean 15.2 against 1.3 weeks with platelets at least 50 x 10^9/L.
Adults, against standard care
FDA-approved- Human trial234 adults who still had a spleen, 52 weeks open-label: treatment failure 11% against 30%, splenectomy 9% against 36%, serious adverse events 23% against 37%.
Children
FDA-approved- Human trial62 children with ITP for at least 6 months: durable response 52% against 10%, any response 71% against 20%, median 12 against 1 weeks with platelets at least 50 x 10^9/L.
- No dataBone marrow reticulin increased in 5 of 27 and 17 of 36 children in two cohorts, at most grade 2, with no collagen fibrosis.
Low platelets during chemotherapy
Investigational- Human trialRECITE, 165 patients with colorectal, gastroesophageal or pancreatic cancer on oxaliplatin: no platelet-driven chemotherapy dose change in cycles 2 and 3 in 84.0% against 36.0% (odds ratio 10.16).
- No dataSerious adverse events 21% against 5% and grade 3 or worse events 37% against 22%, mostly from chemotherapy; events judged related to the study drug 12% against 7%, none serious; blood clots 2% against 0%. In long-term follow-up 53% and 45% died, mostly from cancer progression (stage 4 disease 72% against 61% at entry), with no death tied to the study drug.
Myelodysplastic syndrome
tested-and-failed- Human trial250 patients with lower-risk disease: clinically significant bleeding not reduced (HR 0.83, 95% CI 0.66 to 1.05, P=0.13).
- No dataStudy drug was halted for more leukemia cases at an interim look (HR 2.51); leukemia rates at 5 years were 11.9% against 11.0% (HR 1.06), and deaths were similar (55.7% against 54.2%, HR 1.03), per the label.
Romiplostim is often described as a 14-amino-acid peptide. The sequence IEGPTLRQWLAARA is only its binding domain: the drug is a 538-residue protein of about 59 kDa, two identical 269-residue chains, each a human antibody Fc fragment ending in two copies of the peptide. It is also said to carry two binding domains; that is two per chain and four per molecule. Older sources describe restricted access through the Nplate NEXUS program, removed in December 2011, or call it approved only for chronic ITP, out of date for US adults since October 17, 2019. The myelodysplastic syndrome trial is often cited as proof that it causes leukemia: the study was halted for an interim imbalance (HR 2.51), but at 5 years leukemia rates were 11.9% against 11.0% (HR 1.06) with similar survival, though the label warning remains. For adults with a spleen, 61% is the durable response rate and 56% its difference from placebo; both circulate. RECITE's main result is 84.0% against 36.0% in the NEJM paper and 84.4% against 35.7% in Amgen's figures. Japan's orphan designation is dated 2006 by Amgen and February 2, 2010 by Kyowa Kirin.
The published record
Papers and trials about Romiplostim (Nplate)
416 papers tagged human · 225 not reviews or lab · 61 clinical trial publications
123 registered trials · 25 with posted results
Furthest stage reached: Approved in the US
Counted from Europe PMC indexing, not read by a person; a human tag can land on reviews, commentary or lab papers; clinical trial publications is the narrower count. 474 papers and 100 trials indexed in detail.
At a glance
Four things to know about Romiplostim (Nplate)
Evidence
FDA-approved
Category
Healing and recovery
Common vial
Varies
Half-life
About 3.5 days (median; range 1 to 34 days)
How much, and do you cycle it?
The range, and whether you take breaks.1 mcg/kg weekly to start, adjusted by platelet count up to 10 mcg/kg (label), once a week. Weekly and ongoing, adjusted to the platelet count FDA label
Given every week for as long as it keeps platelets at a safe level, and stopped if platelets have not responded after 4 weeks at the maximum dose. In a study of 75 adults treated within 6 months of diagnosis, 32% stayed in remission for 6 months or more off all ITP medicines.
How long does it stay in the body?
The half-life, and where the figure comes from.About 3.5 days (median; range 1 to 34 days)FDA label
Measured in ITP patients given 3 to 15 mcg/kg weekly, with peak levels 7 to 50 hours after injection (median 14). Levels vary and do not track dose, because platelets carry the receptor and clear the drug: high counts go with low levels. No buildup after six weekly 3 mcg/kg doses in 4 patients.
Source: Nplate US prescribing information (2025), section 12.3
You can compare this against the whole library to see where it sits.
How is it given?
Dosing context and source notes.Given in hospital from a prepared product, so there is nothing to mix.
Label range: 1 up to 10 mcg/kg per week. Nplate US prescribing information (February 2025), section 2
Injected under the skin once a week by a health professional in the US (in the EU, adults with stable platelet counts may inject themselves after training), dosed on actual body weight. Start at 1 mcg/kg and raise it by 1 mcg/kg a week until platelets reach at least 50 x 10^9/L, up to 10 mcg/kg. If platelets are above 200 and up to 400 x 10^9/L for 2 weeks in a row, the dose drops by 1 mcg/kg; above 400 it is held and restarted 1 mcg/kg lower once counts fall below 200. In adult trials, responders needed a median of 2 to 3 mcg/kg; children's weight is rechecked every 12 weeks. It is stopped if platelets have not responded after 4 weeks at 10 mcg/kg. Blood counts are checked weekly while the dose is adjusted, monthly once stable and weekly for at least 2 weeks after stopping. Supplied as freeze-dried powder in single-dose 125, 250 and 500 mcg vials, mixed with sterile water to 500 mcg/mL; doses under 23 mcg are diluted further with saline to 125 mcg/mL. After radiation exposure the dose is a single 10 mcg/kg injection. Given by a health professional and dosed by body weight, so the calculator cannot produce a draw.
How do you store it?
Before mixing, and after.Follow the storage on the product label.
Romiplostim (Nplate) is supplied as a finished product, so its label sets the storage. Pens, prefilled syringes, implants, tablets and ready-made solutions are used as supplied. Kits that include a powder are mixed just before the dose and usually used straight away, not kept for weeks. Many injectable products go in the fridge and must not be frozen, while others are kept at room temperature, so check the pack or ask the pharmacist.
What are the side effects and cautions?
Known cautions and warnings for this compound.Solubility, computed: 36% charged residues, 57% hydrophobic. Water usually sufficient.
A first-pass rule from peptide manufacturers' guidance. It does not account for disulfide bridges, salt form or how the powder was dried, and it predicts what should be easy rather than what will happen in your vial.
Who should avoid it
- None on the US label
- Low platelets from myelodysplastic syndrome or any cause other than ITP: not indicated, and the label warns of progression of myelodysplastic syndrome to acute myeloid leukemia
- Bringing platelet counts up to normal: the label says it should not be used for this
- Pregnancy and breastfeeding: animal data suggest harm to the fetus, and breastfeeding is not advised
Stop and get help
- Signs of a blood clot: a swollen or painful leg, chest pain, sudden breathlessness, or weakness or numbness on one side
- Swelling of the face, lips or throat, or trouble breathing: allergic reactions including anaphylaxis have been reported
Common effects
- Headache in 35% against 32% on placebo, and joint pain in 26% against 20% (adults)
- Dizziness 17%, insomnia 16%, muscle pain 14%, limb pain 13% and abdominal pain 11%, against 0%, 7%, 2%, 5% and 0% on placebo
- In children: bruising 41% against 33%, throat pain 25% against 4%, fever 24% against 8% and diarrhea 20% against 13%
- In an open-label adult study, bone marrow reticulin increased in 7% (9 of 131) and 2% (2 of 132) developed grade 4 collagen fibrosis
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Romiplostim (Nplate) approved?
And where the numbers on this page come from.Yes. Romiplostim (Nplate) is FDA approved and available on prescription in the United States. It is also approved in the European Union and Japan.
- Approval statusFDA-approved
- RouteUnder the skin (weekly injection)
- Checked17 October 2026
- Approved outside the USEuropean Union, Japan: EU authorization of Nplate on February 4, 2009, for adults with chronic ITP, since extended to children 1 year and older; in Japan, Kyowa Kirin sells it as Romiplate, launched April 13, 2011 for chronic ITP and since extended to aplastic anemia. Amgen said in 2019 that Nplate was approved in 69 countries. Biosimilars are authorized in India (Enzene Biosciences, 2021) and Russia (Stimplate, 2023).This does not change the United States position above.
- DoseFrom the drug label. The manufacturer tested this range and a regulator reviewed it.
- Vial sizeFrom what vendors typically list; not a recommendation.
- SourcesDrugs@FDA, BLA 125268 (Nplate)Nplate US prescribing information (February 2025)Nplate original US label (2008)FDA GSRS substance record, romiplostim (UNII GN5XU2DXKV)EMA, Nplate public assessment reportEMA, Nplate EPARCwirla et al., Science 1997;276:1696-1699NICE TA221, data from Kuter DJ et al., Lancet 2008;371:395-403Kuter DJ et al., New England Journal of Medicine 2010;363:1889-1899Giagounidis A et al., Cancer 2014;120:1838-1846OncLive on RECITE (Al-Samkari HT et al., NEJM 2026;394:1061-1073)Amgen, FDA approves Nplate (August 22, 2008)Amgen, Nplate approved for earlier use (October 18, 2019)Kyowa Kirin, Romiplate aplastic anemia expansion (September 25, 2023)
What has happened recently
The FDA approved Nplate (Amgen, BLA 125268) on August 22, 2008, as an orphan drug for chronic ITP in adults with an insufficient response to corticosteroids, immunoglobulins or splenectomy; at first it was available only through a restricted distribution program, Nplate NEXUS, removed in December 2011. Children 1 year and older with ITP for at least 6 months were added on December 14, 2018, newly diagnosed and persistent ITP in adults on October 17, 2019, and a single dose to improve survival after myelosuppressive radiation exposure on January 28, 2021, approved on rhesus monkey data; the latest label is dated February 21, 2025. The EU granted a full authorization on February 4, 2009, at first for adults only (children 1 year and older were added later), and Nplate left the EU orphan register in February 2019 when its market exclusivity ended. In Japan, Kyowa Kirin launched Romiplate on April 13, 2011 and added aplastic anemia in June 2019, broadened in September 2023. Biosimilars have been authorized in India (Enzene Biosciences, August 2021) and Russia (Stimplate, Generium, October 2023); none is approved in the US or EU. Use in low platelets from chemotherapy is in phase 3, and no US filing has been found.
You can compare this against the whole library, or read how to check a seller.
What else is like Romiplostim (Nplate)?
Others in Healing and recovery, side by side.If you're weighing Romiplostim (Nplate), it's worth reading PDA (Pentadeca Arginate), GLOW blend, and KLOW blend in the same class.
A protein drug that carries four copies of a 14-residue peptide to switch on the receptor for thrombopoietin, the hormone that makes platelets. FDA-approved for immune thrombocytopenia since August 22, 2008.
- Dose
- 1 mcg/kg weekly to start, adjusted by platelet count up to 10 mcg/kg (label)
- How often
- Once a week
A newer, more stable cousin of BPC-157 for faster healing.
- Dose
- 0.25 up to 0.5 mg per day (start low, increase slowly)
- How often
- 1-2x daily
A popular skin-and-healing blend of three peptides in one shot.
- Dose
- Community examples use 2 to 2.5 mg of total blend per day, or set the draw by GHK-Cu.
- How often
- Daily
The GLOW blend plus an anti-inflammatory peptide, an all-in-one recovery stack.
- Dose
- Community examples use 2 to 4 mg of total blend per day, or set the draw by GHK-Cu.
- How often
- Daily
Guides for this compound
- How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
- How to Read an Insulin Syringe
Read the units, convert to millilitres, and draw the exact dose.
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
Sources
- Drugs@FDA, BLA 125268 (Nplate)(2026)Approved August 22, 2008; new indications December 14, 2018, October 17, 2019 and January 28, 2021; prescription status.
- Nplate US prescribing information (February 2025)(2025)Weekly 1 to 10 mcg/kg titration; peptibody description; median half-life 3.5 days; adverse reaction tables; myelodysplastic syndrome warning with 5-year leukemia rates.
- Nplate original US label (2008)(2008)Original chronic ITP indication; Nplate NEXUS restricted distribution; reticulin warning; worse thrombocytopenia after stopping in 4 of 57 patients.
- FDA GSRS substance record, romiplostim (UNII GN5XU2DXKV)(2026)Two identical 269-residue chains: methionine, 227-residue IgG1 Fc and a 41-residue peptide segment; CAS 267639-76-9; no modifications.
- EMA, Nplate public assessment report(2009)About 59 kDa; 269 residues per chain; made in E. coli as inclusion bodies; not glycosylated.
- EMA, Nplate EPAR(2026)EU authorization February 4, 2009; removed from the orphan register in February 2019; adult and pediatric ITP indications.
- Cwirla et al., Science 1997;276:1696-1699(1997)Identified IEGPTLRQWLAARA from peptide libraries: about 2 nM affinity; a linked dimer about 4,000-fold more potent than the monomer.
- NICE TA221, data from Kuter DJ et al., Lancet 2008;371:395-403(2011)Durable response 38% against 0% (splenectomized) and 61% against 5% (non-splenectomized); overall response 79% against 0% and 88% against 14%.
- Kuter DJ et al., New England Journal of Medicine 2010;363:1889-1899(2010)234 adults over 52 weeks: treatment failure 11% against 30% and splenectomy 9% against 36% with standard care.
- Giagounidis A et al., Cancer 2014;120:1838-1846(2014)250 patients with lower-risk myelodysplastic syndrome: bleeding endpoint missed (HR 0.83, P=0.13); study drug halted for an interim leukemia imbalance.
- OncLive on RECITE (Al-Samkari HT et al., NEJM 2026;394:1061-1073)(2026)165 patients on oxaliplatin chemotherapy: no platelet-driven dose change in 84.0% against 36.0%; serious adverse events 21% against 5%.
- Amgen, FDA approves Nplate (August 22, 2008)(2008)Described as the first FDA-approved peptibody protein; pooled bleeding of grade 2 or worse 15% against 34%.
- Amgen, Nplate approved for earlier use (October 18, 2019)(2019)75 adults within 6 months of diagnosis: 93% had a response and 32% had remission of 6 months or more off ITP medicines; approved in 69 countries.
- Kyowa Kirin, Romiplate aplastic anemia expansion (September 25, 2023)(2023)Japan extended Romiplate to aplastic anemia including patients not previously given immunosuppressive therapy.
Beyond these, 574 records are indexed. Browse the records