Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1. Pharmacodynamic properties
Pharmacotherapeutic group: Posterior pituitary lobe hormones
ATCcode: H01BB02
Mechanism of action
Oxytocin is a cyclic nonapeptide that is obtained by chemical synthesis. This synthetic form is identical to the natural hormone that is stored in the posterior pituitary and released into the systemic circulation in response to suckling and labour.
Oxytocin stimulates the smooth muscle of the uterus, more powerfully towards the end of pregnancy, during labour, and immediately postpartum. At these times, the oxytocin receptors in the myometrium are increased.
The oxytocin receptors are G-protein-coupled receptors. Activation of receptors by oxytocin triggers release of calcium from intracellular stores and thus leads to myometrial contraction.
Oxytocin elicits rhythmic contractions in upper segment of uterus, similar in frequency, force and duration to those observed during labour.
Being synthetic, oxytocin in Oxytocin -Grindeks does not contain vasopressin, but even in its pure form, oxytocin possesses some weak intrinsic vasopressin-like antidiuretic activity.
Based on in vitro studies, prolonged exposure of oxytocin had been reported to cause desensitization of oxytocin receptors probably due to down-regulation of oxytocin binding sites, destabilization of oxytocin receptors mRNA and internalization of oxytocin receptors.
Plasma levels and onset/duration of effect
Intravenous infusion. When Oxytocin-Grindeks is given by continuous I.V. infusion at doses appropriate for induction or enhancement of labour, the uterine response sets in gradually and usually reaches a steady state within 20 to 40 minutes. The corresponding plasma levels of oxytocin are comparable to those measured during spontaneous first-stage labour. For example, oxytocin plasma levels in 10 pregnant women at term receiving a 4 milliunits per minute intravenous infusion were 2 to 5 microunits/mL. Upon discontinuation of the infusion, or following a substantial reduction in the infusion rate, e.g., in the event of overstimulation, uterine activity declines rapidly but may continue at an adequate lower level.

Pharmacokinetic Properties