8 Questions
List the drugs that cause uterine contraction.
Oxytocics, ergot derivatives, prostaglandins
Explain the mechanism of action of oxytocin.
Oxytocin stimulates uterine contractions by binding to oxytocin receptors on uterine smooth muscle cells, leading to the release of calcium ions and muscle contraction.
List the contraindications for the use of oxytocin.
Abnormal fetal presentation, cephalopelvic disproportion, placenta previa, antepartum hemorrhage, fetal distress, previous cesarean section
Enumerate the obstetric uses of ergot alkaloids and prostaglandin analogues.
Ergot alkaloids: Control and prevent postpartum hemorrhage. Prostaglandin analogues: Used in abortion, cervical priming, postpartum hemorrhage.
Explain the pharmacological basis for using oxytocin in the induction of labour, uterine inertia, and breast engorgement.
Oxytocin induces labor by increasing uterine contractions; in uterine inertia, it helps in controlling contractions with normal relaxation intervals; and in breast engorgement, it stimulates myoepithelial cells for milk let down without increased milk production.
Explain the uterine relaxant action of beta-2 agonists.
Beta-2 agonists bind to beta-2 adrenergic receptors, triggering a cascade that decreases intracellular calcium, leading to reduced uterine contractions.
List tocolytics and mention their therapeutic uses.
Tocolytics: Ritodrine, Isoxsuprine, Salbutamol, Terbutaline, Nifedipine, Atosiban. Therapeutic uses: Delay or postpone premature labor, arrest threatened abortion, treat dysmenorrhea.
Enumerate conditions in which tocolytics are contraindicated.
Tocolytics are contraindicated if amniotic membranes have ruptured, antepartum hemorrhage is occurring, severe toxaemia of pregnancy, intrauterine infection, or fetal death is present.
Study Notes
Uterotonics
- Oxytocics are drugs that cause uterine contraction
- Examples: Oxytocin, Ergot derivatives (Ergometrine and Methylergometrine), Prostaglandins (Misoprostol, Dinoprostone, Carboprost)
Oxytocin
- Mechanism of action: synthesized in the hypothalamus and stored in neurohypophysis
- Therapeutic uses:
- Induction of labour: administered by i.v. infusion to increase intensity, frequency, and duration of uterine contractions
- Uterine inertia: increases uterine contractions to help labour progression
- Postpartum haemorrhage and Caesarean section: contracts uterine smooth muscle to arrest bleeding
- Breast engorgement: stimulates myoepithelial cells to aid milk letdown
Oxytocin vs Ergometrine/PGs
- Oxytocin is the drug of choice for uterine inertia due to:
- Short half-life and controlled i.v. infusion
- Normal relaxation between contractions, preserving foetal oxygenation
- Lower segment is not contracted, allowing for foetal descent
- Consistent augmentation of uterine contractions
Adverse Effects of Oxytocin
- Uterine hyperstimulation: overdosage can cause strong uterine contractions, leading to uterine rupture, fetal asphyxia, or fetal death
- Water intoxication: large fluid infusion can cause headache, vomiting, drowsiness, and convulsions
- Transient hypotension and reflex tachycardia: high dose oxytocin can cause these cardiovascular issues
Contraindications of Oxytocin
- Abnormal foetal presentation
- Cephalopelvic disproportion
- Placenta previa
- Previous caesarean section
- Antepartum haemorrhage
- Foetal distress
Ergot Derivatives
- Examples: Ergometrine and Methylergometrine
- Primary indication: control and prevent postpartum haemorrhage (PPH)
- Used after Caesarean section/instrumental delivery to prevent uterine atony and ensure normal involution of the uterus post-delivery
Prostaglandin Analogues
- Examples: Misoprostol (PGE1), Dinoprostone (PGE2), Carboprost
- Therapeutic uses:
- Abortion: Misoprostol used as adjuvant to mifepristone
- Cervical priming (ripening): Dinoprostone used for dilatation of cervix
- Postpartum haemorrhage: Carboprost used when oxytocin and ergometrine are not effective
- Induction/augmentation of labour: not preferred due to risk of uterine hyperstimulation and rupture
Adverse Effects of Prostaglandins
- Nausea, vomiting
- Syncope, dizziness
- Watery diarrhoea
- Uterine cramps due to excessive forceful uterine contractions
- Vaginal bleeding
Tocolytics
- Examples: Ritodrine, Isoxsuprine, Salbutamol, Terbutaline, Nifedipine, Atosiban (Oxytocin-receptor Antagonist)
- Indications:
- Delay or postpone premature labour
- Arrest threatened abortion
- Dysmenorrhea
- Contraindications:
- Amniotic membranes have ruptured
- Antepartum haemorrhage is occurring
- Severe toxaemia of pregnancy
- Intrauterine infection
- Foetal death
Tocolytic Action of Beta-2 Agonists
- Bind to beta-2 adrenergic receptors of myometrial cells in the uterus
- Stimulate adenylate cyclase to increase cyclic adenosine monophosphate (cAMP)
- Enhances the efflux of calcium from smooth muscle cells
- Decreases formation of activated myosin light chain kinase
- Decreases the intensity and frequency of uterine contractions
This quiz covers the pharmacology of oxytocics and tocolytics, including their mechanisms of action, uses, and adverse effects. It also applies pharmacological knowledge to real-world scenarios.
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