Barusiban and atosiban effects on OT-induced contractions. Top left: A two hour high-dose IV infusion of barusiban at 150 μg kg-1 h-1 decreased IUP within 0.5 h, compared with OT control levels, and the effect was sustained for more than 14 h . Barusiban has a longer duration of action when compared with atosiban. IUP curves were integrated as area under the curve in half hour intervals. Data shown are means ± SD for three animals (n = 1–2 when SD not shown). Top right: A two-hour high-dose IV infusion of atosiban at 250 μg kg-1 h-1 produced similar reductions in IUP, but the effect lasted for only 3-h duration. Both antagonists demonstrated an immediate onset of inhibition of uterine contractions and a high efficacy. Bottom left: PK data showed that the effects of barusiban persisted during declined plasma levels. The plasma samples were analysed with liquid chromatography and tandem mass-spectroscopy. Bottom right: Atosiban effects occurred only during periods of peak plasma concentrations.