DEFINITION
Drugs which stimulate the uterine contractions are called oxytocics or ecbolics.
Oxytocics: These drugs stimulate uterine contractions, promote expulsion of fetus, prevent postpartum hemorrhage, help in the involution of uterus and facilitate expulsion of milk from the mammary glands during lactation. They include oxytocin, ergometrine, methyl ergometrine, prostaglandins-PGF2α, PGE2, misoprostol and quinine.
OXYTOCIN
Oxytocin is a peptide hormone secreted by the posterior pituitary along with ADH. It is synthesized in the Supra-optic and paraventricular nuclei of the hypothalamus, transported along the axon and stored in the neurohypophysis (posterior pituitary). It is released by stimuli such as suckling, coitus and parturition.
Actions: Uterus Oxytocin contracts the uterus. It stimulates pregnant and non-pregnant uterus, but the sensitivity of the uterus to oxytocin increases as the pregnancy advances, reaching a maximum at term. The fundus and the body contract, while the lower segment is relaxed. Both force and frequency of contractions are enhanced and there is full relaxation in between the contraction. At full term, the uterus is highly sensitive to the effects of oxytocin as there is an increase in the number of oxytocin receptors.
- Mammary gland: Oxytocin facilitates milk ejection by contraction of the myoepithelium in the mammary alveoli. Suckling stimulates the release of oxytocin.
- It appears to function as peptide neurotransmitter in brain (CNS).
- It is inactive orally and is usually given IV or can also be given as nasal spray.
Uses: It is used for induction of labor. Oxytocin is used to induce or augment labor when contraction are inadequate, even at full-term of pregnency.
- PPH: As an alternative to ergometrine.
- Milk ejection: When ejection is impaired in nursing mothers, intranasal spray can be used.
- Abortion: As an alternative to induce midtrimester abortion.
- Breast engorgement.
Adverse effects: Large doses cause water intoxication and very powerful contractions of the Uterus, and may lead to soft tissue injury or Uterine rupture.
ERGOMETRINE AND METHYL ERGOMETRINE
Ergometrine is an alkaloid obtained from ergot, while methyl-ergometrine is semi synthetic. Both are active orally, have a rapid onset of effect and are devoid of adrenergic blocking and vasoconstrictor effect present in other ergot alkaloids, viz., ergotoxine, ergotamine and DHE.
Actions: Uterus : Ergometrine is a powerful uterine stimulant. The force and frequency of uterine contractions are enhanced; lower segment also contracts. There is no relaxation in between contraction. Ergometrine stimulates the uterus during all phases of gestation, but the uterus at full-term and immediately after delivery is highly sensitive to its effects.
It has no effect on the mammary gland.
Uses: They are completely absorbed it given orally onset of action—oral – 15 min. IM – 15 min and IV – immediate.
- Postpartum hemorrhage – Ergometrine is used to treat and prevent PPH (Postpartum hemorrhage)
- To hasten uterine involution – Ergometrine is given for 7 days.
- To prevent uterine atony – After cesarean section.
Adverse effects: Adverse effaect inclube nausea, vomiting and rarely hypertension.
PROSTAGLANDINS
- PGE2 and PGF2α stimulate the contraction for both pregnant and non-pregnant uterus though sensitivity is higher during pregnancy.
- They also soften the cervix and hasten dilatation (cervical ripening). PGs produced by fetal tissues mediate initiation and progression of labor .
Uses: It is used for following purpose:
- Abortion: PGs are used as vaginal suppositories to induce midtrimester abortion. They are also used with mifepristone in termination of pregnancy up to 9 weeks.
- PPH: As an alternative to ergometrine.
- Cervical priming: Gels are used intravaginally to soften the cervix.
- Induction of labor: PGs are used as alternatives to oxytocin.
Adverse effects: They include : nausea, vomiting, headache, fever and diarrhea.