Carbetocin is a synthetic analogue of the posterior pituitary lobe hormone oxytocin and has its physiological and pharmacological main effects at the smooth muscle (induction and increase of contractions) of reproductive organs.
Carbetocin has the same effect as natural oxytocin: at the oestrogen stimulated uterus, it causes a change from weak, spontaneous and irregular to synchronised, regular, increased and directed contractions. Moreover, in the mammary gland it produces physiological contractions of the myoepithelial cells in the alveolae and small lactiferous ducts as well as a simultaneous relaxation of the teat sphincter. The action of carbetocin is prolonged and it causes an intensification of the physiological effect.
Carbetocin is, due to its strongly developed peptidase-resistance, more slowly degraded in vivo and distinguishes itself by a prolonged efficacy. Carbetocin is much more lipophilic than exogenously applied oxytocin and therefore, a better distribution and a longer effect on the receptors occur. Beside the stability against proteases, this may also contribute to the prolonged increase of uterine tone activity. After administration of 0.6mg of carbetocin in sows, a bi-compartmental kinetic was observed. The elimination half-life is approximately 85-100 min. There are no essential differences between intramuscular and intravenous administration.