Atosiban is a synthetic peptide analogue of oxytocin, acting as a competitive antagonist at oxytocin and vasopressin V1a receptors. It is a tocolytic agent specifically indicated for the delay of imminent preterm birth in pregnant women with regular uterine contractions of at least 30 seconds' duration at a rate of ≥4 per 30 minutes, a cervical dilation of 1 to 3 cm (0-3 for nulliparas) and effacement of ≥50%, a gestational age from 24 until 33 completed weeks, and a normal fetal heart rate. It is administered via intravenous infusion.
Adult: Intravenous use only. Three-step regimen: 1. Initial bolus: 6.75 mg (in 0.9 ml) injected IV over 1 minute. 2. High-dose infusion: 18 mg/hour (in 5 ml/hour) for 3 hours. 3. Low-dose infusion: 6 mg/hour (in 1.67 ml/hour) for up to 45 hours. Total duration of treatment should not exceed 48 hours. Total cumulative dose should not exceed 330 mg.
Note: Must be administered in a hospital setting with neonatal ICU facilities. The 37.5 mg vial is diluted in specific volumes of 0.9% Sodium Chloride or 5% Dextrose to create the bolus and infusion solutions. Use a dedicated IV line or a Y-connection close to the injection site. Administer using a calibrated infusion pump. Strict aseptic technique is mandatory. Monitor uterine contractions, maternal vital signs, and fetal heart rate continuously.
Atosiban competitively inhibits the action of oxytocin, a hormone that stimulates uterine contractions, by binding to myometrial oxytocin receptors. It also has antagonistic activity at vasopressin V1a receptors. This dual blockade prevents the influx of calcium into myometrial cells, which is necessary for the activation of the contractile apparatus, thereby inhibiting uterine contractions.
Pregnancy: Pregnancy Category B3 (as per Australian categorization). Used specifically in pregnancy (24-33 weeks) for its intended indication. Safety beyond 48 hours of treatment or in multiple courses is not established.
Driving: Dizziness has been reported; patients should be cautioned about driving or operating machinery if they experience such effects. Primarily administered in a hospital setting.
| Other Tocolytic Agents (e.g., Ritodrine, Nifedipine) | Increased risk of pulmonary edema and cardiovascular side effects. Concurrent use is contraindicated. | Major |
| Vasopressors | Atosiban may antagonize the vasoconstrictive effects of vasopressin V1a agonists. Monitor blood pressure. | Moderate |
| Oxytocin | Mutual antagonism. Atosiban will inhibit the uterine stimulant effect of oxytocin. | Major |