Atosiban (Tractocile)

Prescription

Atosiban (brand name Tractocile) is a peptide oxytocin receptor antagonist used to slow or stop premature labor — a treatment known as tocolysis. Where carbetocin and oxytocin are agonists that make the uterus contract, atosiban is the opposite: it competitively blocks oxytocin (and, to a degree, vasopressin V1a) receptors on the uterus, reducing the frequency and force of contractions. It is a modified analog of oxytocin in which key substitutions turn the agonist into an antagonist. The clinical goal of tocolysis with atosiban is not usually to prevent preterm birth outright but to delay it by up to 48 hours. That window is valuable: it allows time to give the mother a course of corticosteroids (which accelerate fetal lung maturation and reduce complications of prematurity), to administer magnesium sulfate for fetal neuroprotection where indicated, and to transfer her to a hospital with an appropriate neonatal intensive care unit. Atosiban is typically given as an initial bolus, then a high-dose loading infusion, followed by a lower maintenance infusion over up to 48 hours. A notable advantage of atosiban is tolerability. Because it acts fairly specifically on uterine oxytocin receptors, it tends to cause fewer maternal cardiovascular side effects than older tocolytics such as beta-agonists (which cause tachycardia and other systemic effects) or calcium-channel blockers. This makes it a favored tocolytic in many European guidelines. Atosiban is approved in the EU, UK, Australia, and numerous other countries but is not FDA-approved in the United States, where other tocolytic strategies are used. It is administered in a hospital obstetric setting with monitoring of both mother and fetus, and its use is guided by gestational age, the clinical situation, and specialist judgment.