A risk-benefit assessment of oxytocics in obstetric practice.

Abstract

Substances that stimulate contractions of the myometrium have found wide applications in present day obstetrics. Above all, fully synthetic, uterus-selective prostaglandin analogues are used for preoperative priming of the cervix for termination of pregnancies in the first trimester as well as for the induction of abortions in the second trimester and have proved to have a much higher efficacy than oxytocin. Because of the pharmacological synergism of their cervix ripening and myometrium stimulating activities, the local use of natural prostaglandin E2 preparations (used intracervically as a gel or vaginally as a gel or as a tablet) is unequivocally superior to use of oxytocin with its almost exclusive contraction stimulating activity for induction of labour, especially for women with an unripe cervix. In women with a ripe cervix, oxytocin and prostaglandins are equally effective with oxytocin having the major advantage of its better controllability on continuous intravenous infusion (plasma elimination half-life of 10 minutes). Over the past 50 years, the use of oxytocin and ergot alkaloids preparations as prophylaxis against postpartum atonia has led to a marked reduction in maternal deaths. The same is true to a major extent for therapy for uterine atonia where the intravenous infusion of dinoprost is an indispensable and life-saving procedure after the failure of systemic administration of oxytocin or ergot alkaloid preparations. On the other hand, the administration of oxytocics can be accompanied by a wide range of adverse systemic and uterine effects and complications ranging from severe cardiovascular incidents with a fatal outcome through to the threat of uterine hyperstimulation with fetal asphyxia to uterine rupture. For these reasons, an adequate knowledge of the pharmacokinetics as well as the systemic and uterine activities and adverse effects of these substances is an essential prerequisite for every physician in evaluating differential indications for their use and adequate monitoring for mother and infant. Of particular importance is the use of prostaglandins for cervical priming prior to termination of pregnancies in the first and second trimesters and the use of native prostaglandin and oxytocin for inducing delivery in cases of fetal deaths as well as vital infants. Both substances play a decisive role at the beginning of delivery. Cervical priming and induction of contractions would not be conceivable without prostaglandin and oxytocin. The pharmacological properties of the 2 substances can be used in different ways for the induction of delivery. Oxytocin ergot alkaloids and prostaglandin are essential for the management of postpartum uterine atonia where their use often represents a decisive, life-saving intervention.