Uterotonic · Hormone

Oxytocin (Pitocin)

Also called Pitocin

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Indications

Induction of labor for a medical reason; not for elective induction (label)
Augmentation of dysfunctional labor (label)
Prevention of postpartum hemorrhage after delivery, IM or IV (ACOG)
Treatment of postpartum hemorrhage from atony, the first-line uterotonic (ACOG PB 183)
Uterine tone at cesarean delivery, as a small slow bolus and an infusion (2019 consensus)
Adjunct for incomplete or inevitable abortion (label)

Dosing

Infusion start: Induction, low dose (ACOG): 0.5–2 milliunits/min (label 0.5–1). Postpartum hemorrhage: 10–40 units in 500–1,000 mL, run to keep the uterus firm, or 10 units IM (ACOG). Cesarean (2019 consensus): 1 unit (3 in labor) IV over at least 30 seconds, then 2.5–7.5 units/h (7.5–15 in labor). Titration: Induction: up 1–2 milliunits/min every 30–60 minutes (label; ACOG low dose every 15–40) to adequate contractions, then hold or cut back. High-dose regimen: start 6, add 3–6 every 15–40 minutes (ACOG).

On the quick cards

Uterotonics: oxytocin, methylergonovine, carboprostNCLEX Drug Classes: Labor induction and postpartum hemorrhage

Mechanism of action

Oxytocin binds the oxytocin receptor, a Gq/11-coupled receptor on myometrial cells. Phospholipase C makes IP₃, which releases calcium from the sarcoplasmic reticulum while more enters through membrane channels; calcium–calmodulin activates myosin light-chain kinase, giving stronger and more frequent contractions, and decidual prostaglandin release adds to them. Receptor numbers rise sharply toward term, so the term uterus is very sensitive, and hours of exposure desensitize and internalize the receptors.

Pharmacology

Uterine: dose-related rise in contraction frequency and force, greatest at term
Breast: contracts myoepithelial cells, ejecting milk
Cardiovascular: a fast IV bolus causes vasodilation, hypotension and reflex tachycardia, with ST changes or myocardial ischemia in some
Renal: likeness to vasopressin gives an antidiuretic effect at high doses, so long infusions in electrolyte-free fluid cause water intoxication and hyponatremia (label)
Fetal: tachysystole cuts placental perfusion between contractions, causing late decelerations and fetal hypoxemia

Pharmacokinetics

Onset	IV almost immediate; IM 3–5 min (label)
Duration	IV effect fades within 1 h of stopping; IM lasts 2–3 h (label)
Steady state	About 40 min after each rate change (Seitchik 1984), the basis of 30–40 min titration steps
Half-life	1–6 min, shorter in late pregnancy (label); some labor studies measured 12–17 min
Distribution	Extracellular fluid (label); small amounts probably reach the fetus
Metabolism	Oxytocinase (placental aminopeptidase) in pregnancy, plus the liver and kidneys
Elimination	Kidneys and liver; little unchanged drug in urine (label)
Routes	IV infusion or IM; never a fast undiluted IV push

Chemistry

A cyclic nonapeptide, Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH₂, with a disulfide bridge between cysteines 1 and 6; C₄₃H₆₆N₁₂O₁₂S₂, MW 1007 (label)
Differs from vasopressin only at positions 3 and 8, which explains its weak antidiuretic and pressor cross-reactivity
Synthetic, so free of the vasopressin in old pituitary extracts (label)
10 units/mL with 0.5% chlorobutanol, pH about 3.5 (Pitocin label); heat degrades many products, hence WHO cold-chain advice, though Pitocin is labeled for room temperature

Adverse effects and cautions

Safety

Labeled for medically indicated induction only, not elective induction
Tachysystole and fetal compromise; uterine rupture, especially after uterine surgery or with high doses
Water intoxication with seizures and coma after long infusions at 40–50 milliunits/min, especially in electrolyte-free fluid (label)
Hypotension, tachycardia and myocardial ischemia with fast boluses: give any bolus over at least 30 s (2019 consensus)
Contraindicated with cephalopelvic disproportion, unfavorable fetal position, fetal distress when delivery is not imminent, a hyperactive uterus or any contraindication to vaginal delivery (label)
Severe hypertension when vasoconstrictors are given with caudal block anesthesia (label)
Long labor exposure desensitizes the receptors, so postpartum atony may need second-line uterotonics early

In the one-pagers

Practice Labor and Fetal Monitoring questions free14 exam-style questions with rationales on the topic where Oxytocin comes up most. No account or download needed.

In the algorithms

Postpartum Hemorrhage

Practice free in your browser2,150+ exam-style questions with rationales. No account, no ads. Also free on the App Store and Google Play.

Sources

FDA label: Pitocin (Par, 2026)
ACOG Practice Bulletins 107 (2009) and 183 (2017)
Heesen 2019 (uterotonics at cesarean)
Seitchik 1984 (oxytocin kinetics)

For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.