Mechanism of action
- Gq protein-coupled receptor agonist → ↑ intracellular Ca²⁺ in myometrial cells → uterine contraction.
- Stimulates myoepithelial cells in mammary tissue → milk ejection (“let-down” reflex).
- Structural homology to Vasopressin (ADH) → cross-reacts w/ V2 receptors in renal collecting ducts at high doses.
Clinical indications
- Postpartum Hemorrhage (PPH): 1st-line agent for prevention and treatment of uterine atony.
- Labor Induction / Augmentation: Indicated for protracted or arrested labor due to inadequate uterine contractions.
- Abortion Management: Adjunct for incomplete, inevitable, or missed abortion in 2nd trimester.
Adverse effects & toxicity
- Hyponatremia / Water Intoxication: c
- Mechanism: ADH-like V2 receptor agonist effect causing free water retention.
- Clinical Picture: Severe hyponatremia, cerebral edema, seizures, encephalopathy, coma.
- Trigger: High-dose, prolonged IV infusion combined w/ hypotonic IV fluids (e.g., D5W).
- Uterine Tachysystole:
- Definition: > 5 contractions in 10 minutes over a 30-minute window.
- Complication: Uteroplacental insufficiency → fetal late decelerations, hypoxia, acidosis.
- Hypotension:
- Occurs w/ rapid IV push due to systemic vasodilation; must give via controlled IV infusion.
- Uterine Rupture:
- Increased risk in pts w/ prior C-section or myomectomy.
Management of oxytocin complications
- Uterine Tachysystole + Abnormal Fetal Heart Rate:
- Discontinue Oxytocin infusion immediately.
- Maternal repositioning (left lateral), O2 administration, IVF bolus.
- If non-reassuring trace persists: Administer tocolytics (e.g., terbutaline).
- Oxytocin-Induced Hyponatremia / Seizures:
- Discontinue Oxytocin infusion and fluid-restrict.
- Administer 3% hypertonic saline for active seizures or severe encephalopathy.