Evidence review: Open Peptide Project (verified against primary PubMed, ClinicalTrials.gov & FDA records) · Last checked 2026-10-27. ← Back to Evidence Library
Romiplostim (Nplate, AMG 531): what the evidence says
At a glance
What it is: a "peptibody": thrombopoietin-mimicking peptides fused to an antibody Fc fragment. Approved as Nplate in Aug 2008 for ITP, and also for the blood-forming syndrome of acute radiation exposure. R1, R2
What the evidence says: Human in two parallel placebo-controlled trials (125 adults with chronic ITP), platelet counts reached safe levels for about 14 of 24 weeks vs under 1 week with placebo. R3 Long-term open-label follow-up supported durable responses. R4
Biggest risks: label warnings: blood clots, progression of myelodysplastic syndrome to leukemia, and persistent low platelets from neutralizing antibodies. R2
Rating
| Human Human evidence | Strong: two RCTs (n = 125) R3 |
| Animal Animal / lab evidence | Not reviewed |
| Regulatory | FDA-approved R1 · not on FDA's 503A or 503B bulk-substance category lists and not on FDA's compounding safety-risk page R5, R6, R7 · not named by WADA R8 |
| Established human dose | Yes, label dose (see Study details) |
Evidence verdict: Immune thrombocytopenia (ITP): Strong (two phase 3 RCTs)
This page reports what studies used. It is not dosing advice.
Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source
About the evidence: two double-blind RCTs plus long-term data; small trials but objective endpoints.
What is it?
Related pages: pegcetacoplan, thymosin-alpha-1.
Does it work?
- Human Platelets ≥50×10⁹/L for 13.8 vs 0.8 weeks. R3
- Human Long-term extension. R4
Is it safe?
- Human Adverse events similar to placebo; no antibodies detected in the RCT. R3
- Label warnings on thrombosis and MDS. R2
Gray-market vials: extra risks
A gray-market vial has no quality control and no guarantee of identity, strength or sterility. We test retail vials blind under the Open Peptide Standard; see /tests/. A passing test covers one batch on one date and does not mean the compound is safe.
Is it legal?
- US: FDA-approved (BLA 125268), prescription. R1
- Compounding: not on FDA's 503A or 503B bulk-substance category lists and not on FDA's compounding safety-risk page. R5, R6, R7
- Sport: not named on WADA's 2026 Prohibited List. R8
Study details
Study details
These are amounts researchers used, not recommendations.
| Study | People / model | Route | Amount used | Follow-up | Reported | Citation |
|---|---|---|---|---|---|---|
| Kuter 2008 | 125 adults, chronic ITP | SC weekly | Per study | 24 weeks | Platelet response 13.8 vs 0.8 weeks | PMID 18242413 |
Full reference list (PubMed, CT.gov, FDA and WADA checked Oct 27, 2026)
- R1 Drugs@FDA, Nplate (romiplostim), application BLA125268 (openFDA drugsfda record checked Oct 27, 2026). https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=BLA125268
- R2 Nplate prescribing information, label published Jun 23, 2026 (DailyMed, checked Oct 27, 2026). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c45f9a58-37c1-4f76-8e36-97d38c577037
- R3 Kuter DJ, et al. Lancet. 2008. PMID 18242413
- R4 Bussel JB, et al. Blood. 2009. PMID 18981291
- R5 FDA, 503A bulk drug substances categories list (updated May 14, 2026). https://www.fda.gov/media/94155/download
- R6 FDA, 503B bulk drug substances categories list (updated Mar 21, 2025). https://www.fda.gov/media/94164/download
- R7 FDA, Certain bulk drug substances for use in compounding that may present significant safety risks (content current Apr 22, 2026). https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- R8 WADA. The 2026 Prohibited List, full list checked; compound not named. https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf
Disclaimer
This page is for education and harm reduction, not medical advice or a recommendation to use Romiplostim (Nplate, AMG 531). This is a prescription medicine. Use it only under the care of a licensed clinician; do not buy it from research-chemical or gray-market sellers. Report problems to FDA MedWatch (https://www.fda.gov/safety/medwatch).