Drug Classification: Labour Induction

UNDER REVIEW (September 2016)

Mechanism of Action:

Ergometrine maleate is an ergot alkaloid which probably acts on 5HT and alpha-adrenergic receptors found in the walls of blood vessels and in the uterus. Ergometrine causes constriction of the blood vessels and contraction of the uterus. Intense contraction of the muscles of the uterus causes the blood supply of the placenta (placental bed) to shrink back into the uterus. It also causes shortening and kinking of the blood vessels in the uterus. Contraction of the muscle in the blood vessel walls causes the blood vessels to narrow and reduces blood flow. Both these actions reduce blood loss following delivery. In normal labour, these contractions occur naturally after delivery, to prevent bleeding from the placental blood source. Ergotmetrine is given if this response is deficient allowing post-partum haemorrhage.

Lecture and CAL materials:

• Lecture:

UNDER REVIEW (September 2016)

Mechanism of Action:

Oxytocin, a peptide hormone released from the posterior pituitary gland, is important in contraction of muscles. Among the effects of oxytocin are: stimulation of lactation (contraction of muscle cells surrounding the alveoli of the mammary gland), and uterine contractions. At the end of pregnancy, oestrogen causes the number of oxytocin receptors to increase, causing the uterus to be more responsive to oxytocin. Synthetic oxytocin is used clinically.

Lecture and CAL materials:

• Lecture:

UNDER REVIEW (September 2016)

Mechanism of Action:

A PGE2 analogue. Activates collagenase in the cervix to hasten ‘ripening’ and dilates the cervix prior to vaginal delivery. It is also associated with contractions of the uterus that are probably a direct effect.

Lecture and CAL materials:

• Lecture: