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Pharmacology - Uterine Stimulants & Relaxants
Questions and Answers (100% Correct Answers)
What are uterine stimulants used for?
Ans: - to induce and/or augment labour
- to reduce postpartum bleeding
Name three examples of uterine stimulants.
Ans: - oxytocin
- ergometrine (ergonovine)
- prostaglandins
Without the aid of exogenous uterine stimulants, what initiates the onset of labour?
Ans: Although circulating blood levels of oxytocin do not change markedly
throughout pregnancy, it is likely that there is an augmented number of oxytocin
receptors in the uterus makes the muscle increasingly responsive to plasma
oxytocin. It is probable that the concentration of receptors responsive to oxytocin
increases in the uterine musculature in response to the increasing levels of estrogen
during pregnancy.
=> concentration of receptors rises by 100-200 times
What type of molecule is oxytocin?
Ans: A peptide hormone.
Where is oxytocin synthesized, stored, and released?
Ans: Oxytocin is synthesized in the hypothalamus, stored in secretory granules in
nerve endings in the posterior pituitary gland, and secreted by the posterior pituitary
into the blood.
How long is the half life of oxytocin?
Ans: Approx 15 minutes.
How is oxytocin eliminated?
Ans: It is primarily inactivated in the kidneys and the liver.
What effect does oxytocin have at a low dose?
Ans: It increases the frequency and force of uterine contractions.
What effect does oxytocin have at a high dose?
Ans: It causes sustained uterine contracture.
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For induction, how is oxytocin given?
Ans: Infusion via iv.
For active management of the third stage, how is oxytocin given?
Ans: 10 IUs IM or SC.
What are some of the adverse effects of using exogenous oxytocin for labour
induction?
Ans: - uterine rupture
- fetal hypoxia (b/c contractions cut off O2 to fetus)
- fluid retention
- hypotension
- reflex tachycardia
Why is fluid retention a concern with oxytocin induction?
Ans: Prolonged use of oxytocin can lead to water intoxication secondary to the anti-
diuretic hormone-like effects of oxytocin; water intoxication is rare but can lead to
seizures and death.
What are the contraindications to oxytocin induction?
Ans: - cervix not yet dilated
- 'unfavourable' fetal presentation (i.e. transverse lie)
- fetal distress
What is ergometrine?
Ans: An ergot alkaloid produced by Claviceps purpurea, a fungus that infects grain,
especially rye. Ergometrine stimulate uterine smooth muscle directly, thereby
increasing muscular tone and enhancing the rate and force of rhythmical
contractions.
What effect does ergometrine have at a low dose?
Ans: Causes rhythmic contraction (with relaxation) of uterus.
What effect does ergometrine have at a high dose?
Ans: Causes sustained contracture.
When is ergometrine used?
Ans: Not typically for induction, because the margin between producing rhythmic
contraction and sustained contracture is narrow, as opposed to oxytocin.
Ergometrine is used more often for preventing PPH, as it has rapid onset of action (5-
15 minutes).
Pharmacology - Uterine Stimulants & Relaxants
Questions and Answers (100% Correct Answers)
What are uterine stimulants used for?
Ans: - to induce and/or augment labour
- to reduce postpartum bleeding
Name three examples of uterine stimulants.
Ans: - oxytocin
- ergometrine (ergonovine)
- prostaglandins
Without the aid of exogenous uterine stimulants, what initiates the onset of labour?
Ans: Although circulating blood levels of oxytocin do not change markedly
throughout pregnancy, it is likely that there is an augmented number of oxytocin
receptors in the uterus makes the muscle increasingly responsive to plasma
oxytocin. It is probable that the concentration of receptors responsive to oxytocin
increases in the uterine musculature in response to the increasing levels of estrogen
during pregnancy.
=> concentration of receptors rises by 100-200 times
What type of molecule is oxytocin?
Ans: A peptide hormone.
Where is oxytocin synthesized, stored, and released?
Ans: Oxytocin is synthesized in the hypothalamus, stored in secretory granules in
nerve endings in the posterior pituitary gland, and secreted by the posterior pituitary
into the blood.
How long is the half life of oxytocin?
Ans: Approx 15 minutes.
How is oxytocin eliminated?
Ans: It is primarily inactivated in the kidneys and the liver.
What effect does oxytocin have at a low dose?
Ans: It increases the frequency and force of uterine contractions.
What effect does oxytocin have at a high dose?
Ans: It causes sustained uterine contracture.
, 2 Inquire through: | Professional | Confidential Support
For induction, how is oxytocin given?
Ans: Infusion via iv.
For active management of the third stage, how is oxytocin given?
Ans: 10 IUs IM or SC.
What are some of the adverse effects of using exogenous oxytocin for labour
induction?
Ans: - uterine rupture
- fetal hypoxia (b/c contractions cut off O2 to fetus)
- fluid retention
- hypotension
- reflex tachycardia
Why is fluid retention a concern with oxytocin induction?
Ans: Prolonged use of oxytocin can lead to water intoxication secondary to the anti-
diuretic hormone-like effects of oxytocin; water intoxication is rare but can lead to
seizures and death.
What are the contraindications to oxytocin induction?
Ans: - cervix not yet dilated
- 'unfavourable' fetal presentation (i.e. transverse lie)
- fetal distress
What is ergometrine?
Ans: An ergot alkaloid produced by Claviceps purpurea, a fungus that infects grain,
especially rye. Ergometrine stimulate uterine smooth muscle directly, thereby
increasing muscular tone and enhancing the rate and force of rhythmical
contractions.
What effect does ergometrine have at a low dose?
Ans: Causes rhythmic contraction (with relaxation) of uterus.
What effect does ergometrine have at a high dose?
Ans: Causes sustained contracture.
When is ergometrine used?
Ans: Not typically for induction, because the margin between producing rhythmic
contraction and sustained contracture is narrow, as opposed to oxytocin.
Ergometrine is used more often for preventing PPH, as it has rapid onset of action (5-
15 minutes).
