Atosiban (Tractocile)_Dosage, benefits & legal status
Also known as Tractocile, Tractocil, Antocin, Atosiban SUN, RWJ-22164, ORF-22164, atosiban acetate
A modified oxytocin that blocks oxytocin and vasopressin receptors on the womb. EU-approved since 2000; a 2025 placebo trial found no benefit for babies.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Atosiban (Tractocile)?
Plain language first. The technical label stays, but it never stands alone.Overview
In threatened preterm labour, a delay of 48 hours lets doctors give steroids for the baby's lungs and move the mother to a hospital with a neonatal unit. Atosiban stops contractions with fewer side effects than older beta-agonist drugs. It has not been shown to help babies: in the 752-woman APOSTEL 8 trial (2025), death or serious illness occurred in 8% against 9% on placebo, and WHO recommends nifedipine instead.
Atosiban is a cyclic oxytocin analogue: deaminated at position 1 (a mercaptopropionyl unit), with O-ethyl-D-tyrosine at 2, threonine at 4, ornithine at 8, a disulfide ring and an amidated end. It competitively blocks oxytocin receptors and vasopressin V1a receptors on uterine muscle, binding V1a about 20-fold more tightly in vendor-cited data (Ki 3.5 against 81 nanomolar). Ferring developed it; a US application by R.W. Johnson (Antocin) went to an FDA advisory committee in 1998 and was never approved.
What it's used for
A hospital intravenous treatment in the EU and UK to delay imminent preterm birth at 24 to 33 weeks of pregnancy. Not available in the US.
How does Atosiban (Tractocile) work?
What it does in the body, and where.Atosiban sits in the receptors that oxytocin and vasopressin use to make the womb contract.
- 01Why contractions startLate in pregnancy the womb carries many more oxytocin receptors. Oxytocin binding them raises calcium in the muscle and drives contractions; vasopressin acting on V1a receptors adds to this.
- 02Blocking the signalAtosiban occupies both receptors without switching them on. Contractions fall within about 10 minutes, and the womb settles to 4 or fewer contractions an hour for about 12 hours.
- 03What it buysThe aim is 48 hours for steroid injections and transfer to a specialist unit. At term only about 12% of the mother's level reaches the baby's blood. It does not treat what started labour.
A schematic of the compound's mechanism, not a diagnostic image.
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.
Against beta-agonists
Clinical use- Human trial742 women: 59.6% against 47.7% undelivered without other drugs at 7 days; beta-agonist failures were mostly for side effects.
Against nifedipine
Clinical use- Human trialAPOSTEL III, 510 women at 25 to 34 weeks: serious outcomes for babies 15% with atosiban against 14% with nifedipine.
Against placebo
tested-and-failed- Human trialAPOSTEL 8, 752 women at 30 to 34 weeks: death or serious illness in babies 8% against 9%; perinatal deaths 0.7% against 0.9%.
US placebo trial
Clinical use- No data15 of 288 fetuses or infants died with atosiban against 5 of 295 with placebo; 11 of the 15 were at 20 to 24 weeks, where 19 women got atosiban and 4 placebo, and beyond 24 weeks rates were similar (1.5% against 1.7%).
It blocks vasopressin V1a receptors more strongly than oxytocin receptors (vendor-cited Ki 3.5 against 81 nanomolar), so 'oxytocin blocker' is only half the story. 'EU-approved' does not mean it helps babies: APOSTEL 8 (Lancet 2025) and the 2014 Cochrane review found no benefit over placebo on major outcomes, and WHO prefers nifedipine. The excess infant deaths in the US placebo trial are often quoted without the imbalance in very early pregnancies behind most of them. The US story is disputed: an FDA committee reviewed it in 1998, but whether the FDA rejected it or the company withdrew is not documented in a primary source. One summary of APOSTEL 8 reported 1% maternal mortality; there were no maternal deaths.
The published record
Papers and trials about Atosiban (Tractocile)
268 papers tagged human · 181 not reviews or lab · 64 clinical trial publications
23 registered trials · 2 with posted results
Furthest stage reached: Approved outside the US, European Union, United Kingdom, Switzerland
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. 454 papers and 23 trials indexed in detail.
At a glance
Four things to know about Atosiban (Tractocile)
Evidence
Clinical use
Category
Sexual and hormonal
Common vial
Varies
Half-life
About 1.7 hours (a first phase of about 13 minutes)
How much, and do you cycle it?
The range, and whether you take breaks.6.75 mg bolus, then 300 and later 100 mcg/min for up to 48 hours (EU label), one course of up to 48 hours. One course of up to 48 hours Clinical use
Given once for up to 48 hours; it may be repeated if contractions return.
About 1.7 hours (a first phase of about 13 minutes)clinical-guideline
Terminal half-life 1.7 hours, plus or minus 0.3. Steady state within about an hour at 300 micrograms a minute. 46 to 48% protein-bound. Small amounts pass into breast milk; the main metabolite, M1, is about 10 times weaker.
Source: Tractocile EU summary of product characteristics, section 5.2
You can compare this against the whole library to see where it sits.
What does it cost?
Typical dose and cost, in plain numbers.Atosiban (Tractocile) is not reconstituted
It is not supplied as a powder measured in milligrams, so there is no water-to-powder math and no draw to calculate here. Doses are written in mg, from a ready-made solution.
Typical dose: 6.75 mg bolus, then 300 and later 100 mcg/min for up to 48 hours (EU label)
Three steps, up to 48 hours: a 6.75 mg intravenous bolus over 1 minute, then 300 micrograms a minute (18 mg an hour) for 3 hours, then 100 micrograms a minute (6 mg an hour) for up to 45 hours. The whole course should not exceed 330.75 mg. It can be restarted with the same sequence; the label advises no more than three re-treatments in one pregnancy. Supplied as a 6.75 mg/0.9 mL injection and a 37.5 mg/5 mL concentrate diluted to 0.75 mg/mL, so there is nothing to mix from powder.
How do you store it?
Before mixing, and after.Given in hospital or a trial clinic, so the pharmacy stores it.
Atosiban (Tractocile) goes into a vein and is prepared by hospital, clinic or trial pharmacy staff, following the product label or the trial protocol. Some products like this are ready-made solutions and others are powders mixed just before use, often with hours rather than weeks of shelf life once prepared. It is not a medicine people store at home.
What are the side effects and cautions?
Known cautions and warnings for this compound.Solubility, computed: 33% charged residues, 44% 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
- Pregnancy under 24 or over 33 completed weeks
- Waters broken after 30 weeks, or suspected infection in the womb
- Abnormal fetal heart rate, death of the fetus, or bleeding needing immediate delivery
- Eclampsia or severe pre-eclampsia, placenta praevia or placental abruption
- Allergy to atosiban or its ingredients
Stop and get help
- Breathlessness or chest tightness, possible fluid on the lungs (more likely with twins or other labour-stopping drugs)
- Fever, abdominal pain or abnormal discharge, possible infection in the womb
Common effects
- Nausea in 14% of treated women
- Headache, dizziness, hot flushes, vomiting, fast heart rate, low blood pressure, injection-site reactions and high blood sugar in 1 to 10%
- Side effects needing treatment to stop were far rarer than with beta-agonists (relative risk 0.05)
- In a US placebo trial, 15 of 288 fetuses or infants died against 5 of 295; 11 of the 15 were at 20 to 24 weeks, where more women had been given atosiban, and beyond 24 weeks the rates were similar (1.5% against 1.7%)
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Atosiban (Tractocile) approved?
And where the numbers on this page come from.Not in the United States. Atosiban (Tractocile) has no FDA approval. It is approved in the European Union, the United Kingdom, and Switzerland.
- Approval statusClinical use
- RouteInto a vein (bolus, then infusion)
- Checked15 October 2026
- Approved outside the USEuropean Union, United Kingdom, Switzerland: EU authorisation of Tractocile on 20 January 2000 and of the generic Atosiban SUN on 31 July 2013; Ferring holds a separate Great Britain licence and sells Tractocile in Switzerland. It was reported in 2007 as approved in 67 countries, not including the US or Japan. Not approved in the US or Canada.This does not change the United States position above.
- DoseFrom product labeling and clinical guidelines.
- Vial sizeFrom what vendors typically list; not a recommendation.
- SourcesEMA, Tractocile EPARTractocile EU summary of product characteristicsEMA, Atosiban SUN EPARTractocile UK summary of product characteristics (emc)FDA GSRS substance record, atosiban (UNII 081D12SI0Z)Federal Register, 26 March 1998van Vliet EOG et al., Lancet 2016;387:2117-2124 (APOSTEL III)van der Windt LI et al., Lancet 2025;405:1004-1013 (APOSTEL 8)Flenady V et al., Cochrane review CD004452 (2014)Cochrane network meta-analysis of tocolytics, CD014978 (2022)Compendium.ch, Tractocile (Switzerland)WHO recommendation on tocolytic therapy (2022)WHO Model List of Essential Medicines, search for atosibanCayman Chemical, atosibanRomero R et al., American Journal of Obstetrics and Gynecology 2000;182:1173-1183
What has happened recently
The EU authorised Tractocile (Ferring) on 20 January 2000 to delay imminent preterm birth at 24 to 33 weeks in adult women meeting set criteria; the first generic, Atosiban SUN, followed on 31 July 2013; Great Britain has its own licence, and Tractocile is also sold in Switzerland and many other countries. It has never been approved in the US: the FDA's reproductive health advisory committee reviewed NDA 20-797 (Antocin, R.W. Johnson) on 20 April 1998, and accounts differ on whether the FDA refused it or the company withdrew. It has no Canadian authorisation and is not on the WHO essential medicines list; WHO's 2022 guidance recommends nifedipine for this use.
You can compare this against the whole library, or read how to check a seller.
What else is like Atosiban (Tractocile)?
Others in Sexual and hormonal, side by side.If you're weighing Atosiban (Tractocile), it's worth reading Cabergoline, Carbetocin (Pabal, Duratocin), and Cetrorelix (Cetrotide) in the same class.
A modified oxytocin that blocks oxytocin and vasopressin receptors on the womb. EU-approved since 2000; a 2025 placebo trial found no benefit for babies.
- Dose
- 6.75 mg bolus, then 300 and later 100 mcg/min for up to 48 hours (EU label)
- How often
- One course of up to 48 hours
A prolactin drug whose label asks for an echocardiogram before the first dose.
- Dose
- 0.25 up to 1 mg per dose, twice a week
- How often
- Twice a week
A modified oxytocin with a carbon-sulfur ring that keeps the womb contracted for hours after one injection. Matched oxytocin in a 29,645-woman trial.
- Dose
- 100 mcg once, after the baby is delivered (label)
- How often
- Once
A GnRH antagonist used in IVF to stop an egg being released too early.
- Dose
- Set by the label
- How often
- Daily during an IVF cycle
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
- EMA, Tractocile EPAR(2022)EU authorisation 20 January 2000; Ferring Pharmaceuticals A/S.
- Tractocile EU summary of product characteristics(2022)Indication at 24 to 33 weeks; three-step dosing; nausea 14%; half-life 1.7 hours; 59.6% against 47.7% undelivered at 7 days against beta-agonists.
- EMA, Atosiban SUN EPAR(2024)First EU generic, authorised 31 July 2013.
- Tractocile UK summary of product characteristics (emc)(2021)Great Britain licence; fetal and infant deaths in the placebo trial broken down by week of pregnancy.
- FDA GSRS substance record, atosiban (UNII 081D12SI0Z)(2026)C43H67N11O12S2, MW 994.2; CAS 90779-69-4; residue names and disulfide.
- Federal Register, 26 March 1998(1998)FDA advisory committee meeting on 20 April 1998 to discuss NDA 20-797, Antocin (R.W. Johnson).
- van Vliet EOG et al., Lancet 2016;387:2117-2124 (APOSTEL III)(2016)510 women: serious outcomes for babies 14% with nifedipine against 15% with atosiban (RR 0.91).
- van der Windt LI et al., Lancet 2025;405:1004-1013 (APOSTEL 8)(2025)752 women at 30 to 34 weeks: death or serious illness in babies 8% against 9% on placebo (RR 0.90, 95% CI 0.58 to 1.40).
- Flenady V et al., Cochrane review CD004452 (2014)(2014)No better than placebo on major outcomes; fewer maternal side effects than beta-agonists.
- Cochrane network meta-analysis of tocolytics, CD014978 (2022)(2022)Oxytocin receptor antagonists probably delay birth by 48 hours compared with placebo (RR 1.13, 95% CI 1.05 to 1.22); effects on neonatal and perinatal deaths uncertain.
- Compendium.ch, Tractocile (Switzerland)(2026)Tractocile 6.75 mg/0.9 mL listed in Switzerland, Ferring AG.
- WHO recommendation on tocolytic therapy (2022)(2022)Recommends nifedipine; oxytocin receptor antagonists are costlier and less widely available.
- WHO Model List of Essential Medicines, search for atosiban(2026)Atosiban is not on the list.
- Cayman Chemical, atosiban(2026)Ki 81 nM at oxytocin receptors and 3.5 nM at V1a receptors (citing Cirillo 2003); sold for research only.
- Romero R et al., American Journal of Obstetrics and Gynecology 2000;182:1173-1183(2000)The US placebo-controlled trial behind the Antocin application.
Beyond these, 477 records are indexed. Browse the records