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Pharmacological particulars
Pharmacotherapeutic group: antiprogestogen.
ATCvet code: QG03XB90.
Pharmacodynamic properties
Aglepristone is a synthetic steroid counteracting the effect of progesterone by competing with this hormone at the level of the uterine receptors, resulting in abortion (or resorption) within 7 days after administration.
Aglepristone does not modify progesterone, prostaglandins, oxytocin or cortisol plasma concentration within 24 hours after its administration but it induces a discharge of prolactin within 12 hours.
In vitro, the affinity of aglepristone for the progesterone receptors in the uterus of the dog is 3 times higher than that of progesterone.
The relative binding affinity of aglepristone to glucocorticoid receptors is similar to that of dexamethasone but aglepristone has antagonistic properties.
Pharmacokinetic properties
After 2 injections of 10 mg/kg/day at a 24-hour interval, the maximal concentration (about 280 ng/ml) is reached after 2.5 days. The mean residence time is around 6 days: this period includes the mean absorption time from the injection site.
After administration of a 10 mg/kg radio-labelled dose, the excretion of radioactivity is very slow. Only 60 % of the administered dose is excreted during the first 10 days and around 80 % over 24 days.
Excretion is essentially via the faeces (around 90 %).