Oxytocin
Pitocin
Endogenous nonapeptide / uterotonic
Stimulates uterine smooth muscle contraction (uterine OXTR receptors). ADH-like action at high doses.
Indications
- •Labor induction/augmentation
- •Postpartum uterine atony
- •Active management 3rd stage labor
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Labor induction | 1–2 mU/min, titrate q15–30 min | — |
| Post-delivery (cesarean) | Slow bolus 1–3 IU + 10–40 IU/L infusion | — |
| Post-delivery (vaginal) | 10 IU IM | — |
Pharmacokinetics
Onset 1 min IV. Half-life 1–6 min.
Hemodynamic effects
Rapid IV bolus → hypotension, tachycardia, arrhythmia. ALWAYS dilute and slow push.
Side effects
- !Hypotension (vasodilation) — especially with rapid IV push
- !Hyponatremia + water intoxication with prolonged high-dose infusion (ADH effect)
- !Tachyphylaxis with prolonged use
- !Coronary vasoconstriction (reported)
Contraindications
- ×Tetanic uterine contractions
- ×Fetal distress with full uterine tone
Clinical pearls
- ★NEVER bolus 10 IU rapid IV — has caused cardiac arrest in OB.
- ★Cesarean: 'Rule of 3s' — 3 IU slow IV, 3 min wait, repeat 3 IU if uterus soft, max 3 doses, then second-line.
- ★Second-line for atony: methylergonovine, carboprost (Hemabate), misoprostol.
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Other drugs in OB / GYN Related
- Carboprost (Hemabate)
15-methylated synthetic analog of prostaglandin F2α. Binds prostaglandin F receptors on uterine smooth muscle → potent contraction. Also constricts pulmonary smooth muscle → BRONCHOSPASM (contraindication in asthma).
- Methylergonovine (Methergine)
Direct uterine smooth muscle stimulant — potent + sustained contraction. Also vasoconstrictor (especially coronary + cerebral arteries) → CONTRAINDICATED in HTN, preeclampsia, CAD.
- Misoprostol (Cytotec)
Synthetic PGE1 analog. Binds prostaglandin E receptors on uterine smooth muscle → contraction. Also: cytoprotective gastric mucosa (original indication for NSAID-induced ulcers); cervical ripening; GI motility.
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