Page data last changed: . Chemistry registry snapshot: . Registry refreshes and identity assessments are separate from scientific content review.
A modified oxytocin peptide that blocks rather than triggers uterine contraction.
Also known as: Tractocile
Part of the Foundational & therapeutic peptides cluster
Overview
Atosiban is a synthetic nonapeptide, a desamino-oxytocin analog that competitively antagonizes oxytocin and vasopressin receptors. By blocking oxytocin-driven calcium release in uterine muscle it suppresses contractions, and it is approved in many countries as a tocolytic to delay preterm birth. Content here is educational only.
Source & context
Biological / chemical source: Synthetic desamino-oxytocin nonapeptide analog
Primary research or clinical context: Approved (outside the US) to delay preterm labor
Turning an agonist into a blocker
Modifying key residues of oxytocin converts the natural agonist into a receptor antagonist. Atosiban is a striking example of how targeted substitutions can flip a peptide's pharmacology from activating to blocking its receptor.
Tocolytic role
By quieting uterine oxytocin receptors, atosiban aims to postpone premature delivery during a defined window of pregnancy. Its receptor-selective mechanism is often contrasted with older, less specific tocolytic drugs in obstetric pharmacology.
Sequence
One-letter sequence commonly cited for Atosiban (educational; isoforms and modifications may differ):
XYITNCPXG
X = non-canonical residue (Residue 1 is mercaptopropanoic acid (deamino-cysteine of the natural sequenec of oxytocin), residue 2 is D-Tyr(2Et), residue 8 is ornithine; disulphide bridge between cysteine residue 6 and N-terminal Mpa). X marks a non-canonical residue — see the structure block below. (Plotted as alanine on the wheel.)
Residues plotted ~100° apart around an α-helix — clustering of one color reveals an amphipathic face.
Structure & chemistry
Molecular identity & reference confidence
Source-supported reference
Reference values are taken from the cited molecular record or curated profile. A database match is not independent laboratory verification; modifications, counter-ions, and formulations can change the measured mass.
- Molecular form
- Atosiban (source record; form not independently established)
- Species
- Not established by this molecular identity audit
- Termini (N / C)
- Not specified / Not specified
Average reference mass
Reference policy updated: 2026-10-05
- IUPHAR/BPS source snapshot · 2026-10-01
- PubChem molecular record · 2026-10-01
- Molecular formula
- C43H67N11O12S2
- Average reference mass
- ≈ 994.2
- Status
- Approved medicine in at least one jurisdiction (IUPHAR record)
Residue 1 is mercaptopropanoic acid (deamino-cysteine of the natural sequenec of oxytocin), residue 2 is D-Tyr(2Et), residue 8 is ornithine; disulphide bridge between cysteine residue 6 and N-terminal Mpa
- PubChem CID: 5311010
- IUPHAR ligand: 2213
- ChEMBL: CHEMBL382301
- CAS RN: 90779-69-4
- UNII: 081D12SI0Z
Chemistry values: IUPHAR/BPS Guide to Pharmacology, PubChem · fetched 2026-10-01.
Clinical development snapshot
ClinicalTrials.gov lists 23 registered studies with “Atosiban” as an intervention (snapshot 2026-09-06). A registry footprint is not evidence of efficacy or approval.
| NCT | Title | Phase | Status | Updated |
|---|---|---|---|---|
| NCT07185230 | Atosiban in Women With Previous Implantation Failure and Abnormal Uterine Contractions | Not applicable | recruiting | 2025-12-09 |
| NCT07140237 | The Effect of Oral Oxytocin and Atosiban on Top-down Attention ( OTAtosiban ) | Early phase 1 | recruiting | 2025-09-08 |
| NCT07093060 | The Effect of Oral Oxytocin and Atosiban on Social Attention | Early phase 1 | recruiting | 2025-07-30 |
| NCT06537778 | Perioperative Use of Atosiban for Ultrasound-indicated Cerclage to Reduce Spontaneous Preterm Birth(sPTB) | Not applicable | completed | 2025-05-22 |
| NCT05693688 | Atosiban Versus Placebo in the Treatment of Late Threatened Pre-term Birth | Phase 4 | completed | 2024-07-25 |
| NCT04468568 | In Utero Repair of Myelomeningocele: Atosiban Versus Terbutaline | — | completed | 2022-06-06 |
Atosiban — reconstitution calculator
Enter how much peptide is in the vial and how much diluent (e.g. bacteriostatic water) is added. The tool returns the resulting solution concentration — and, for any amount you type, the volume it corresponds to. This is educational arithmetic, not a dosing recommendation.
Reference form: Atosiban (source record; form not independently established)Average reference mass: 994.2 Da
Enter an amount to see the volume it corresponds to.
Educational concentration mathematics only. This tool does not recommend a dose, amount, or protocol, and nothing here is medical advice. Many peptides are not authorized by Health Canada for human use — see our reconstitution and bacteriostatic-water guides for context.
FAQ about Atosiban
What is Atosiban?+
Atosiban is a synthetic nonapeptide, a desamino-oxytocin analog that competitively antagonizes oxytocin and vasopressin receptors. By blocking oxytocin-driven calcium release in uterine muscle it suppresses contractions, and it is approved in many countries as a tocolytic to delay preterm birth. Content here is educational only.
What Canadian product status is recorded for Atosiban?+
Canadian product status for Atosiban has not been verified in this profile. No verified record here does not mean no authorization exists. Status depends on the product, formulation and use; consult Health Canada's product records.
What is the typical length of Atosiban?+
Atosiban is commonly described as approximately 9 amino acids (Oxytocin antagonist).
Related peptides
References & further reading
- 1.van der Windt et al. (2025). Atosiban versus placebo for threatened preterm birth (APOSTEL 8): a multicentre, randomised controlled trial. Lancet
- 2.Shubert (1995). Atosiban. Clin Obstet Gynecol
- 3.Wang et al. (2023). Efficacy of atosiban for repeated embryo implantation failure: A systematic review and meta-analysis. Front Endocrinol (Lausanne)
- 4.Hadar et al. (2013). Effect of an oxytocin receptor antagonist (atosiban) on uterine electrical activity. Am J Obstet Gynecol
- 5.Saade et al. (2021). Randomized Trials of Retosiban Versus Placebo or Atosiban in Spontaneous Preterm Labor. Am J Perinatol
- 6.van Winden et al. (2020). Effects of tocolysis with nifedipine or atosiban on child outcome: follow-up of the APOSTEL III trial. BJOG
- 7.Tsatsaris et al. (2004). Atosiban for preterm labour. Drugs
- 8.Manning et al. (2001). Design of oxytocin antagonists, which are more selective than atosiban. J Pept Sci
- 9.PubChem — compound summary for Atosiban (CID 5311010)
- 10.Wikipedia — Atosiban