Uteroactive Drugs
Uteroactive drugs are medications that influence uterine contractions. They are widely used in obstetrics to manage labor, delivery, postpartum hemorrhage, and preterm labor.
Classification
- Oxytocics (Stimulate uterine contractions):
- Oxytocin
- Misoprostol
- Ergometrine
- Tocolytics (Inhibit uterine contractions):
- Nifedipine
- Terbutaline
Pharmacodynamics
- Oxytocin: Binds to oxytocin receptors → ↑ intracellular calcium → uterine smooth muscle contraction
- Misoprostol: Prostaglandin E1 analog → activates prostaglandin receptors → ↑ calcium → uterine contraction
- Ergometrine: Acts on α-adrenergic, serotonin, and dopamine receptors → powerful sustained uterine contraction
- Nifedipine: Calcium channel blocker → ↓ calcium influx → relaxation of uterine muscle
- Terbutaline: β2-adrenergic agonist → ↑ cAMP → relaxation of uterine smooth muscle
Side Effects
- Common:
- Nausea, vomiting
- Flushing, headache
- Abdominal discomfort
- Rare/Severe:
- Uterine rupture (especially with oxytocics)
- Severe hypotension (nifedipine, ergometrine)
- Arrhythmias
- Allergic reactions
- Excessive bleeding
Drug Interactions
- Nifedipine:
- Potentiates effects of other antihypertensives
- Metabolism affected by CYP3A4 inducers/inhibitors
- Terbutaline:
- ↓ efficacy with beta-blockers
- ↑ cardiovascular risk with other sympathomimetics
- Ergometrine:
- Risk of hypertension with vasoconstrictors
- ↑ toxicity with macrolides (e.g. erythromycin)