Atosiban is an inhibitor of the hormones oxytocin and vasopressin. It is used as an intravenous medication as a labour repressant (tocolytic) to halt premature labor. Although initial studies suggested it could be used as a nasal spray and hence would not require hospital admission, it is not used in that form. Originally it is licensed in proprietary and generic forms for the delay of imminent pre-term birth in pregnant adult women.
Atosiban is a nonapeptide, desamino-oxytocin analogue, and a competitive vasopressin/oxytocin receptor antagonist (VOTra). Atosiban inhibits the oxytocin-mediated release of inositol trisphosphate from the myometrial cell membrane. As a result, reduced release of intracellular, stored calcium from the sarcoplasmic reticulum of myometrial cells and reduced influx of Ca2+ from the extracellular space through voltage-gated channels occur. In addition, atosiban suppresses oxytocin-mediated release of PGE and PGF from the decidua.
In human preterm labour, atosiban, at the recommended dosage, antagonises uterine contractions and induces uterine quiescence. The onset of uterus relaxation following atosiban is rapid, uterine contractions being significantly reduced within 10 minutes to achieve stable uterine quiescence.
