Atosiban SUN

The mechanism of action of the active substance is based on its role as an antagonist of human oxytocin at the receptor level.‍‍‍‍‍‍​​​‍​​​​​​ As a result, uterine muscle tone and contraction frequency are reduced. In summary, uterine quiescence is induced. Pharmacokinetic studies have shown that in women receiving the active substance by infusion (300 μg/min) for 6–12 hours, mean steady-state plasma concentrations of 442 ng/ml were achieved within 1 hour. Atosiban is 46–48% bound to plasma proteins. The mean volume of distribution was approximately 18.3 ± 6.8 litres. The active substance does not penetrate into red blood cells. There are two metabolites of the active substance formed by cleavage of the peptide bond between ornithine and proline. The larger fragment retains activity as an oxytocin receptor antagonist but is 10 times less potent than the parent compound. Small amounts of atosiban are found in urine, while a 50-fold greater amount is present as a metabolite. The amount of drug excreted in faeces is unknown.