Drugs acting on the uterus play pivotal roles in various obstetric and gynecological settings, including labor induction, management of postpartum hemorrhage, prevention of preterm labor, and medical abortion.
1) Uterine Stimulants (Oxytocics) (Drugs Acting on the Uterus):
A) Oxytocin:
Source: Produced in the hypothalamus, secreted by the posterior pituitary.
Actions: Stimulates uterine contractions and milk ejection.
Uses: Induction of labor, postpartum hemorrhage control.
Side Effects: Uterine hyperstimulation, fetal distress, water intoxication (ADH-like effect).
B) Ergot Alkaloids (Methylergonovine):
Mechanism: Stimulates sustained uterine contractions.
Uses: Postpartum hemorrhage control.
Side Effects: Hypertension, nausea, vomiting, headache.
C) Prostaglandins (e.g., Dinoprostone, Misoprostol):
Mechanism: Cause cervical ripening and stimulate uterine contractions.
Uses: Labor induction, medical abortion (with mifepristone), postpartum hemorrhage.
Side Effects: GI disturbances (nausea, diarrhea), uterine hypertonus, fetal distress.
2) Uterine Relaxants (Tocolytics):
A) Beta-2 Agonists (e.g., Terbutaline):
Mechanism: Relax uterine smooth muscle.
Uses: Delay preterm labor (short-term).
Side Effects: Tachycardia, hyperglycemia, hypokalemia.
B) Calcium Channel Blockers (e.g., Nifedipine):
Mechanism: Inhibit calcium entry, reducing uterine contractions.
Uses: Preterm labor.
Side Effects: Hypotension, headache, flushing.
C) NSAIDs (e.g., Indomethacin):
Mechanism: Inhibit prostaglandin synthesis, reducing contractions.
Uses: Short-term tocolysis.
Side Effects: Premature ductus arteriosus closure, oligohydramnios.
D) Magnesium Sulfate:
Mechanism: Relaxes uterine muscles and provides fetal neuroprotection.
Uses: Preterm labor, seizure prevention in eclampsia.
Side Effects: Respiratory depression, hypotension, cardiac arrhythmias.
3) Other Uterine Agents:
A) Progesterone Agonists (e.g., Progesterone, Dydrogesterone):
Uses: Support pregnancy and prevent preterm labor.
B) Antiprogestins (e.g., Mifepristone):
Uses: Medical abortion and hyperprolactinemia management.
Clinical Applications of Uterine Drugs:
Labor Induction and Augmentation: Ensures timely and effective delivery.
Postpartum Hemorrhage Management: Prevents and controls excessive bleeding.
Preterm Labor Management: Delays delivery for fetal maturation.
Medical Abortion: Non-surgical pregnancy termination.
Pregnancy Support: Maintains pregnancy in high-risk cases.
Side Effects and Considerations:
Uterotonics: Risk of uterine hyperstimulation, fetal distress, maternal hypertension.
Uterine Relaxants: Cardiovascular effects, maternal hypoxia, electrolyte imbalances.
General Considerations: Monitor maternal and fetal well-being; avoid in contraindications like cardiovascular disease and fetal anomalies.