📋 Clinical Overview

Atosiban is a synthetic peptide analogue of oxytocin and a competitive antagonist of vasopressin (V1a receptor). It is a tocolytic agent specifically indicated for the delay of imminent preterm birth in pregnant women with a gestational age of 24 to 33 completed weeks, regular uterine contractions (at least four per 30 minutes), and cervical dilation of 1 to 3 cm (0-3 cm for nulliparas) and effacement of ≥ 50%. It works by inhibiting uterine contractions.

💊 Dosage & Administration

Adult: Three-step intravenous regimen: 1. Initial Bolus: 6.75 mg (one vial) injected slowly over 1 minute. 2. High-dose Infusion: Immediately follow with 300 micrograms/min infusion for 3 hours (prepared as 5 mL Atosiban concentrate [37.5 mg] in 100 mL isotonic saline or 5% dextrose). 3. Low-dose Infusion: Follow with 100 micrograms/min infusion for up to 45 hours (prepared as 5 mL Atosiban concentrate [37.5 mg] in 250 mL isotonic saline or 5% dextrose). Total duration of treatment should not exceed 48 hours.

Note: For intravenous use only. Must be administered in a hospital with neonatal intensive care facilities. The 6.75 mg bolus is administered as a slow IV injection over 1 minute. The subsequent infusions must be administered via an infusion pump. Do not mix with other drugs in the same infusion line. Use isotonic saline or 5% dextrose as diluent.

⚠️ Contraindications

Gestational age below 24 weeks or over 33 completed weeks.
Premature rupture of membranes (PROM) after 30 weeks of gestation.
Intrauterine fetal death.
Ectopic pregnancy.
Antepartum uterine hemorrhage requiring immediate delivery.
Conditions of the mother or fetus where continuation of pregnancy is hazardous (e.g., severe pre-eclampsia, eclampsia, chorioamnionitis, placental abruption).
Known hypersensitivity to Atosiban or any component of the formulation.
Severe hepatic impairment.

🔬 Mechanism of Action

Atosiban competitively inhibits the actions of oxytocin and vasopressin at their respective uterine receptors (oxytocin and V1a receptors). This blockade prevents the receptor-mediated influx of calcium into myometrial cells, which is necessary for the activation of the contractile apparatus, thereby inhibiting uterine contractions.

🤕 Side Effects

Nausea
Headache
Dizziness
Hot flushes
Tachycardia (maternal)
Hypotension
Vomiting
Hyperglycemia
Injection site reaction

🤰 Special Populations

Pregnancy: Pregnancy Category B3 (as per Australian categorization; US FDA has not assigned a formal category). Used specifically in pregnancy (24-33 weeks) for its tocolytic effect. Should only be used when clearly indicated. No adequate data on use in first trimester.

Driving: Dizziness and nausea may occur; patients should be cautioned against driving or operating machinery if these symptoms are experienced. Treatment is inpatient, so this is not typically relevant.

🔄 Drug Interactions

Other Tocolytic Agents (e.g., Ritodrine, Nifedipine)	Increased risk of cardiovascular side effects (pulmonary edema, arrhythmias). Concurrent use is not recommended.	Major
Corticosteroids (e.g., Betamethasone, Dexamethasone)	Concomitant use for fetal lung maturation is standard. Monitor for fluid overload and pulmonary edema, especially with beta-agonists.	Moderate
Vasopressor Agents	Atosiban may antagonize the vasoconstrictive effects of vasopressin analogues.	Moderate
Oxytocin	Pharmacological antagonism. Atosiban will inhibit the uterine stimulant effect of oxytocin.	Major

Nobosiban