Atosiban
A drug that quiets contractions to delay preterm birth, authorised in Europe and never approved in the US
Atosiban blocks the oxytocin receptor, damping the contractions of preterm labour. Authorised in the EU as Tractocile since 2000 for a 48-hour intravenous course, it delays birth, but a 2025 trial found no benefit for babies against placebo.
What is it?
Oxytocin drives the contractions of labour; atosiban occupies its receptor without activating it. Drugs of this kind, tocolytics, are given to delay a birth that has started too early. Whether that delay improves outcomes for the baby is the question the trials keep asking.
The European product information sets tight limits: a 6.75 mg intravenous bolus, then 300 micrograms a minute for three hours, then 100 micrograms a minute, for no more than 48 hours in all, in women between 24 and 33 completed weeks with regular contractions, a cervix dilated 1 to 3 cm and a normal foetal heart rate. Atosiban is not approved in the US.
Against other tocolytics it held its own. Against placebo the record is weaker: the first large trial missed its primary endpoint, and in 2025 APOSTEL 8 found no benefit for babies between 30 and 34 weeks.
Against other tocolytics it compares well. In 761 women it held off birth for 48 hours more often than hexoprenaline, with less tachycardia and palpitations, and against ritodrine pregnancy lasted about as long. In twins, repeated courses were associated with longer pregnancies in a matched cohort. Pulmonary oedema is a rare but reported harm, mostly in multiple pregnancies.
A second use has grown in IVF, where the idea is to calm uterine contractions around embryo transfer. Observational studies pooled in a 2023 meta-analysis looked positive, but the randomised trials did not confirm it: in 1,100 women with previous implantation failure, live birth was 49.5% against 44.7% on placebo, not significant, with a possible benefit only in women with abnormal contractions.
Mechanism of Action
Atosiban is a peptide that blocks the oxytocin receptor without activating it, reducing uterine contractions.
Oxytocin receptor blockade
It occupies the receptor that drives labour contractions, delaying preterm birth for up to 48 hours.
Uterine contractility in IVF
It is tested around embryo transfer to reduce contractions; benefit appeared mainly in women with abnormal contractions.
Fewer heart-rate effects
Compared with hexoprenaline it caused less tachycardia and palpitations.
Published Research
These are the trials in people, read from their PubMed abstracts, with dosing from the Tractocile product information read October 1, 2026.
The placebo-controlled trial
In 501 women in preterm labour, atosiban did not lengthen the time to delivery or treatment failure (median 25.6 against 21.0 days, p = 0.6), though more women stayed undelivered without another tocolytic at 24 hours, 48 hours and 7 days. The benefit held from 28 weeks; below 24 weeks, foetal and infant deaths were more frequent with atosiban.
Against salbutamol
In 241 women randomised to atosiban or salbutamol, 93.3% and 95.0% were undelivered at 48 hours, and 89.9% and 90.1% at 7 days. Maternal adverse events, serious ones included, were more frequent with salbutamol, and outcomes for the babies were comparable.
Implantation failure: 1,100-woman RCT
In 1,100 women with previous implantation failure having frozen blastocyst transfer, live birth was 49.5% on atosiban against 44.7% on placebo, not significant (risk ratio 1.11); in the subgroup with abnormal uterine contractions it was 51.9% against 39.3%.
Recurrent implantation failure, double-blind
In women with recurrent implantation failure undergoing IVF, live birth was 42.3% on atosiban against 35.1% on placebo, not significant, with no differences in pregnancy, miscarriage or implantation rates.
Dosing protocols in implantation failure
In a double-blind trial comparing two atosiban protocols before embryo transfer, the infusion protocol trended toward more live births (20.0% against 6.0%) without reaching significance.
Against hexoprenaline
In 761 women in a retrospective study, atosiban was more effective than hexoprenaline at delaying birth for 48 hours, with less tachycardia and palpitations and no difference in longer-term tocolysis.
Against ritodrine
In a multicentre retrospective comparison with ritodrine, pregnancy duration was similar overall, with longer maintenance on atosiban only in multiple pregnancies.
Repeated courses in twins
In matched twin pregnancies with threatened preterm labour, continuous and repeated atosiban courses were associated with longer pregnancy (hazard ratio 0.58) and more complete antenatal steroid courses.
Adding ebopiprant
In 113 women receiving atosiban for preterm labour, adding oral ebopiprant was associated with fewer deliveries within 48 hours (12.5% against 21.8%), a difference that was not significant.
Fetal surgery
During fetal myelomeningocele repair, women given terbutaline had more acidosis and higher lactate than those given atosiban in a 25-patient retrospective cohort.
Against nifedipine
An individual participant data meta-analysis of four trials (791 women) found no difference in a composite of serious outcomes for the baby (16% after nifedipine, 19% after atosiban). Nifedipine delayed birth longer, 18 days against 10, and perinatal deaths were 3.6% against 1.8%, a difference that was not significant.
APOSTEL 8: against placebo again
In 752 women with threatened preterm birth at 30 to 34 weeks, the composite of perinatal death and severe neonatal illness occurred in 8% of babies after atosiban and 9% after placebo (RR 0.90, 95% CI 0.58 to 1.40). Maternal adverse events did not differ; the authors question the standard use of atosiban at these gestations.
IVF meta-analysis
Pooling 2 randomised trials and 5 cohort studies in repeated implantation failure, atosiban was associated with a higher clinical pregnancy rate (risk ratio 1.54); most included studies were observational.
Pulmonary oedema
A systematic review found 7 cases of acute pulmonary oedema linked to atosiban, mostly in multiple pregnancies, about 40 hours after starting; some began after the infusion had ended.
Dosing Data
Not approved in the US. The EU label (Tractocile) sets a three-step intravenous regimen for no more than 48 hours.
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
Reported Side Effects
From the Tractocile product information and the trials.
Contraindications & Cautions
From the product information.
Legal Status
Authorised in the EU; not approved in the US.
Frequently Asked Questions
?What is atosiban used for?
To delay imminent preterm birth, for at most 48 hours; it is authorised in the EU, not in the US.
?Does it improve outcomes for the baby?
Not in the trials against placebo: APOSTEL 8 in 2025 found no reduction in infant death or serious illness at 30 to 34 weeks.
?How does it compare with other tocolytics?
As well as salbutamol with fewer side effects; nifedipine delayed birth longer, with similar outcomes for babies.
?Is atosiban used in IVF?
It has been tested around embryo transfer. Observational studies looked positive, but in a 1,100-woman randomised trial live birth was 49.5% against 44.7% on placebo, not significant, with a possible benefit only in women with abnormal uterine contractions.
?What are its main risks?
Compared with hexoprenaline it caused less tachycardia and palpitations. A systematic review found 7 cases of acute pulmonary oedema, mostly in multiple pregnancies.
References
- [other] Tractocile (atosiban) summary of product characteristics, sections 4.1, 4.2, 4.3, 4.8 and 5.2, European Medicines Agency product information (first authorisation January 20, 2000; read October 1, 2026).
- [pubmed] Romero R, et al. "An oxytocin receptor antagonist (atosiban) in the treatment of preterm labor: a randomized, double-blind, placebo-controlled trial with tocolytic rescue." Am J Obstet Gynecol, 2000;182(5):1173-83. PMID: 10819855.
- [pubmed] "Treatment of preterm labor with the oxytocin antagonist atosiban: a double-blind, randomized, controlled comparison with salbutamol." Eur J Obstet Gynecol Reprod Biol, 2001;98(2):177-85. PMID: 11574128.
- [pubmed] van Winden TMS, et al. "Tocolysis with nifedipine versus atosiban and perinatal outcome: an individual participant data meta-analysis." BMC Pregnancy Childbirth, 2022;22(1):567. PMID: 35840927.
- [pubmed] van der Windt LI, et al. "Atosiban versus placebo for threatened preterm birth (APOSTEL 8): a multicentre, randomised controlled trial." Lancet, 2025;405(10483):1004-1013. PMID: 40049187.
- [pubmed] Flenady V, et al. "Oxytocin receptor antagonists for inhibiting preterm labour." Cochrane Database Syst Rev, 2014;2014(6):CD004452. PMID: 24903678.
- [pubmed] Cai H, et al. "Atosiban in individuals with previous implantation failure undergoing frozen blastocyst transfer: a randomized controlled trial." Hum Reprod, 2025;40(5):808-817. PMID: 40036869.
- [pubmed] Tang CL, et al. "A randomized double blind comparison of atosiban in patients with recurrent implantation failure undergoing IVF treatment." Reprod Biol Endocrinol, 2022;20(1):124. PMID: 35986323.
- [pubmed] Wang R, et al. "Efficacy of atosiban for repeated embryo implantation failure: A systematic review and meta-analysis." Front Endocrinol (Lausanne), 2023;14:1161707. PMID: 37033236.
- [pubmed] Chuang MT, et al. "Different dosage protocols of atosiban in repeated implantation failure before embryo transfer: A double-blind randomized controlled trial." Taiwan J Obstet Gynecol, 2026;65(3):433-439. PMID: 42036176.
- [pubmed] Kirchhoff E, et al. "Hexoprenaline Compared with Atosiban as Tocolytic Treatment for Preterm Labor." Geburtshilfe Frauenheilkd, 2022;82(8):852-858. PMID: 35967742.
- [pubmed] Kim GW, et al. "A multicenter, retrospective comparison of pregnancy outcomes between groups of preterm labor nulliparous mothers treated with atosiban vs. ritodrine in singleton and multiple pregnancies." Taiwan J Obstet Gynecol, 2023;62(5):682-686. PMID: 37678995.
- [pubmed] Zhu H, et al. "The effectiveness and safety of continuous and repeated treatment of atosiban in twin pregnancy with threatened preterm labor: A propensity score-matched study." PLoS One, 2025;20(7):e0328008. PMID: 40632745.
- [pubmed] Mol BW, et al. "Efficacy and safety of ebopiprant to delay preterm birth after oral administration in pregnant women with spontaneous preterm labor receiving atosiban: a phase 2a, double-blind, parallel group, randomized, placebo-controlled, proof of concept study." Eur J Obstet Gynecol Reprod Biol, 2025;313:114637. PMID: 40782442.
- [pubmed] Andrade Santos S, et al. "Comparison of terbutaline and atosiban as tocolytic agents in intrauterine repair of myelomeningocele: a retrospective cohort study." Braz J Anesthesiol, 2024;74(3):844495. PMID: 38521500.
- [pubmed] Yang Z, et al. "Atosiban-induced acute pulmonary edema: A rare but severe complication of tocolysis." Heliyon, 2023;9(5):e15829. PMID: 37305518.
Sources & Citations
Dosing from the EMA product information (read October 1, 2026); studies were read from their PubMed abstracts. Read October 7, 2026.
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