Quick Facts

• Primary Use: May assist in delaying imminent pre-term birth.
• Intended Population: Pregnant adult women between 24 and 33 completed weeks of gestation who exhibit signs of pre-term labor.

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Atosiban is a medication utilized in obstetrics to manage certain instances of pre-term labor. Its principal role is to potentially delay imminent pre-term birth in pregnant adult women. This temporary delay may afford critical time for the administration of other necessary treatments, such as corticosteroids, to support fetal development.

The use of Atosiban is specifically directed toward patients who present with regular uterine contractions and corresponding cervical changes, within the gestational age window of 24 to 33 completed weeks, and who have a normal fetal heart rate. The medication is an option for care when the continuation of the pregnancy is deemed safe for both the mother and the fetus.

By helping to reduce the frequency of uterine contractions, Atosiban aims to achieve uterine quiescence, which may assist in maintaining the pregnancy for a brief, designated period. Treatment with the medication should be conducted by healthcare professionals with experience in managing pre-term labor.

Regulatory References

1. EMA therapeutic overview

Eligibility Scope

Atosiban is indicated only for pregnant adult women (age 18 years and older) who are experiencing signs of imminent pre-term birth. Use is strictly limited to a documented gestational age between 24 and 33 completed weeks and requires a normal foetal heart rate along with specific labor criteria.

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Contraindications and Restrictions

The medicine must not be used (contraindicated) in patients with the following conditions:

• Gestational age below 24 or over 33 completed weeks.
• Known hypersensitivity to Atosiban or any of its components.
• Severe conditions requiring immediate delivery, such as eclampsia and severe pre-eclampsia or antepartum uterine haemorrhage.
• Confirmed intrauterine foetal death, abnormal foetal heart rate, or suspected intrauterine infection.
• Conditions like placenta praevia or abruptio placenta.

Use with Caution:

• There is limited clinical experience regarding use in multiple pregnancies and in the gestational age group of 24 to 27 weeks.
• It should be used with caution in patients with impaired hepatic function due to a lack of clinical experience. Use is not established in pregnant women less than 18 years old.
• Breast-feeding should be discontinued during treatment, as small amounts of Atosiban pass into breast milk.

Interactions with other medicines and products

The interaction profile for Atosiban is defined by official regulatory findings regarding its use alongside other medicines, and no drug combinations are formally listed as contraindicated due to interaction risk.

Pharmacodynamic Interactions

Co-administration with other medicinal products classified as tocolytic agents, such as calcium channel blockers or beta-mimetics, is documented to be associated with an increased risk of pulmonary oedema. This outcome is considered a significant additive pharmacodynamic interaction as stated in the official prescribing information.

Metabolic and Pharmacokinetic Status

Atosiban is considered unlikely to be involved in drug-drug interactions mediated by the cytochrome P450 (CYP) enzyme system. Official in vitro investigations confirm that Atosiban is neither a substrate for the CYP450 system nor an inhibitor of the drug-metabolising CYP450 enzymes.

Specific pharmacokinetic studies examined co-administration with commonly used agents. No clinically relevant interaction was observed with Betamethasone. When Labetalol was co-administered, its maximum plasma concentration (C max) decreased and the time to C max increased; however, the overall exposure measured by the Area Under the Curve (AUC) remained unchanged, leading to the regulatory conclusion of no clinically relevant interaction.

Population-Specific Caution

Due to limited clinical experience and the potential for altered clearance, regulatory documents specify that Atosiban should be used with caution in patients who have impaired hepatic function.

How Atosiban Works: Mechanism of Action

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Blocking Oxytocin and Vasopressin Receptors

Atosiban acts primarily as a competitive antagonist at the myometrial (uterine muscle) oxytocin receptor (OTR) and exhibits antagonistic activity at the vasopressin V1a receptor. By binding to these receptors, it suppresses the signaling normally initiated by the body's natural hormones, oxytocin and vasopressin.

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Inhibiting the Intracellular Calcium Cascade

This receptor blockade prevents the activation of the downstream Gq protein signaling pathway, which is responsible for the release of intracellular calcium (Ca^2+). Limiting the availability of this key ion interrupts the molecular sequence necessary for muscle contraction.

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Reducing Uterine Smooth Muscle Contraction

The overall consequence of interrupting the calcium cascade is the inhibition of myosin light-chain phosphorylation and subsequent relaxation of the uterine smooth muscle. This modulation of contractile pathways leads to a reduction in uterine tone and motility, which constitutes the final observable physiological effect.

Atosiban is administered exclusively via the intravenous (IV) route as a highly structured, time-limited course of therapy. The treatment must be initiated and maintained under the supervision of a physician experienced in managing the relevant clinical condition, commencing as soon as possible after diagnosis.

Administration utilizes two distinct forms: a solution for injection for the initial dose and a concentrate for infusion for the subsequent stages. The concentrate must be diluted with specified infusion fluids, such as 0.9% Sodium Chloride or 5% Glucose, prior to its continuous administration.

Standard Use Protocol (Maximum 48 Hours)	Dose and Rate	Duration
Stage 1 (Initial Bolus)	6.75 mg (undiluted)	Over 1 minute
Stage 2 (High-Dose Infusion)	300 mu g/ min	3 hours
Stage 3 (Low-Dose Infusion)	100 mu g/ min	Up to 45 hours

The entire course of therapy for a single episode must not exceed 48 hours, limiting the total delivered amount of Atosiban. If a patient requires re-treatment, administration must begin again with the full three-stage protocol. Regarding patient populations, the medication should be used with caution in patients with impaired hepatic function, although no dose adjustment is typically needed for renal impairment. Rules for use are not established for pregnant women under 18 years of age.

Research Evidence / Overview of Studies for Atosiban

Evidence for Use in Threatened Pre-term Labor

The primary body of research for Atosiban involves a series of Randomized Controlled Trials (RCTs) and subsequent meta-analyses. These studies were conducted during periods of increased uterine activity, and Atosiban was studied for threatened pre-term labor. Researchers observed women, typically between 24 and 33 completed weeks of gestation, who were experiencing regular contractions and changes to the cervix. In these research scenarios, Atosiban was evaluated in comparison to both a placebo (an inactive treatment) and to other medications observed for quieting the uterus. The main outcomes research examined were the duration of delivery delay and various measures of the newborn's health status.

Focus on Delivery Delay and Gestational Age

Studies monitored how symptoms evolved in the observed populations by measuring the time from the start of treatment until delivery. The key research endpoints were defined intervals, such as delaying birth for at least 48 hours or 7 days. Findings describe patterns observed in the studies related to these short-term delays. Research also monitored the gestational age at which delivery occurred. The evidence contributes to understanding the short-term changes in delivery timing, particularly when Atosiban was evaluated in comparison to a placebo or other active treatments.

Focus on Neonatal Outcomes Studied

Research has also explored outcomes related to the health of the newborn, such as those monitoring breathing function or strain. The clinical trials closely monitored several major neonatal outcomes, including the incidence of perinatal mortality and severe complications like respiratory distress syndrome. One pattern observed in studies comparing Atosiban to certain other agents was a difference in the reported rate of maternal adverse events. Major meta-analyses focusing on the baby's health often indicated that findings were mixed, suggesting that a definitive pattern related to a significant change in major neonatal outcomes remains uncertain across the entire evidence landscape.

Evidence in Special Pregnancy Subgroups

The core research results apply only to the specific populations studied, and data for certain groups remain insufficient. Evidence remains limited for some populations. For example, regulatory documents note that limited clinical experience is documented for women who presented at the earliest stages of gestation, between 24 and 27 completed weeks. Research has also examined temporary physiological imbalance in women with twin pregnancies.

Common questions about Atosiban (FAQ)

Q: How quickly does the effect of the medicine wear off after the infusion stops, and can contractions return?

According to the official product information, the medicine has a very short effective half-life of approximately 18 minutes. This means the concentration of the drug in the body drops rapidly once the continuous infusion is discontinued. Because the effect wears off quickly, contractions may return. The drug's official regulatory documentation notes that the treatment can be repeated up to three more times during the same pregnancy, if clinically necessary.

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Q: What warnings exist regarding pre-existing heart problems?

Official warnings state that the medicine should be used with caution, particularly in cases of multiple pregnancy or if other tocolytic (contraction-delaying) medications are being used simultaneously. This combination is associated with an increased risk of pulmonary oedema (fluid in the lungs), which is listed as a serious adverse reaction in official safety documents.

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Q: Where can I find the official research and clinical trial data for this medication?

Official information on the clinical studies used to approve this medication can be found on government-affiliated clinical trial registers, such as the European Union Clinical Trials Register (EudraCT) or the United States’ ClinicalTrials.gov. These sites are the standard repositories that display protocols and results related to the use and safety of authorised medicines.

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Q: Why is urine output monitored during the infusion?

Although only a small amount of the active substance is excreted through the urine, official caution is advised for patients who may have impaired kidney function. The monitoring of urine output and fluid balance serves as part of the established clinical management protocols during the intravenous infusion.

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Q: Are there any drugs that decrease the effectiveness of the treatment?

Official studies indicate no clinically relevant drug interactions have been found with specific agents such as labetalol or betamethasone. Official prescribing information indicates that if uterine contractions continue despite treatment, the clinical setting may necessitate consideration of alternative therapies.

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Q: What are the symptoms and management for an accidental overdose?

The regulatory documents note that few cases of atosiban overdose have been reported in clinical experience. These cases generally occurred without specific or unusual signs or symptoms. The official product information states that there is no known specific treatment required in the event of an overdose.

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Q: What are the brand names and alternative names for this medication?

The active substance is called atosiban. The medicine is marketed under various trade names globally, with the original brand name being Tractocile. It is also available under several trade names for the generic substance, such as Atosiban SUN.

Atosiban concentrate for solution for infusion must be stored in a refrigerator at a temperature between 2 C and 8 C. It is essential to keep the vials in the original package to protect the medicine from light. The product should not be used if particulate matter or discoloration is visible prior to administration.

Once the solution is diluted for intravenous use, it must be used within 24 hours of preparation. Do not use Atosiban after the expiration date printed on the label.

Proper disposal of Atosiban and related materials is crucial to protect the environment. Do not dispose of unused or expired medicine via wastewater or household waste. Instead, consult a pharmacist or healthcare provider for instructions on how to safely and responsibly discard unneeded medicines, following local requirements for pharmaceutical waste.