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Oxytocics: Classification, Mechanism, Therapeutic Uses, and Adverse Effects
Classification of Oxytocics
- Natural Oxytocics: Oxytocin (hormone from posterior pituitary)
- Synthetic Oxytocics: Carbetocin, Misoprostol, Prostaglandins (e.g., dinoprostone, carboprost)
Mechanism of Action
- Oxytocin: Binds to receptors on uterine smooth muscle, increasing intracellular calcium, leading to contraction.
- Prostaglandins: Increase intracellular calcium to induce contractions.
- Ergot Alkaloids: Stimulate alpha-adrenergic receptors, causing vasoconstriction and uterine contraction.
Therapeutic Uses
- Induction of Labor: Used when spontaneous labor is delayed.
- Postpartum Hemorrhage: Helps reduce bleeding by promoting uterine contractions.
- Medical Abortion: Misoprostol used in combination with mifepristone.
Adverse Effects
Oxytocin:
- Water intoxication
- Uterine hyperstimulation
- Nausea, vomiting, hypotension
Misoprostol:
- Diarrhea
- Abdominal cramps
- Fever
Ergot Alkaloids:
- Vasoconstriction leading to hypertension
- Uterine tetany
- Nausea and vomiting
Contraindications
Oxytocin:
- Fetal distress
- Placenta previa, abnormal fetal position
- Previous cesarean section
Misoprostol:
- History of cesarean section
- Cardiovascular disease
Ergot Alkaloids:
- Not used in obstetrics due to severe side effects
- Contraindicated in pregnancy
Why Ergot Derivatives Are Not Used as Oxytocics
Ergot derivatives are no longer commonly used as oxytocics due to their severe side effects. They cause significant vasoconstriction, leading to hypertension and ischemia, and can induce uterine tetany, which increases the risk of uterine rupture. Additionally, they are less effective in inducing labor and are primarily used for postpartum hemorrhage management. For safer alternatives, oxytocin and prostaglandins are preferred.
