SYNTOCINON

Clinical safety rating: caution

Comprehensive clinical and safety monograph for SYNTOCINON (SYNTOCINON).

How it works

Synthetic oxytocin binds to oxytocin receptors in the myometrium, causing increased intracellular calcium and uterine smooth muscle contraction. Also acts on mammary gland myoepithelium for milk ejection.

What the body does with it

Metabolism	Rapidly metabolized in the liver and kidneys by oxytocinase (cysteine aminopeptidase) and other peptidases.
Excretion	Renal: >99% as intact oxytocin; biliary/fecal: negligible (<1%).
Half-life	Terminal elimination half-life: 1–6 minutes (intravenous); 1–9 minutes (intramuscular). Clinically, effects dissipate rapidly after infusion cessation.
Protein binding	Low (~30%); primarily binds to albumin and oxytocin-specific carrier proteins (e.g., neurophysin I).
Volume of Distribution	0.2–0.3 L/kg; reflects limited distribution into extracellular fluid and minimal tissue binding.
Bioavailability	Intramuscular: ~20–40% (due to rapid enzymatic degradation); Intravenous: 100%.
Onset of Action	Intravenous: 1–2 minutes; Intramuscular: 3–5 minutes.
Duration of Action	Intravenous: 15–60 minutes (dose-dependent); Intramuscular: 30–120 minutes. Uterine response wanes quickly after infusion stop.

Classification & Brands

Action Class	Uterotonic and abortificient
Brand Substitutes	Itocin 5IU Injection, Wotocin 5IU Injection, Indox 5IU Injection, Zygon 5IU Injection, Labtocin 5IU Injection

Dosing & administration

10 units (1 mL) intravenously as a single dose after delivery; continuous infusion: 20 units in 1 L of normal saline or lactated Ringer's solution at 2-10 mU/min (0.1-0.5 mL/min) titrated to uterine response.

Dosage form	INJECTABLE
Renal impairment	No dosage adjustment required for renal impairment; oxytocin is rapidly metabolized and renally excreted, but no specific GFR-based guidelines exist.
Liver impairment	No dosage adjustment required for hepatic impairment; oxytocin is metabolized primarily by the liver, but no Child-Pugh based modifications have been established.
Pediatric use	Not indicated for pediatric use; safety and efficacy in children have not been established.
Geriatric use	Use with caution in elderly patients due to potential for uterine hyperstimulation and adverse cardiovascular effects; no specific dosage adjustments recommended.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for SYNTOCINON (SYNTOCINON).

Breastfeeding	Oxytocin is endogenous in breast milk; exogenous administration does not significantly increase milk levels. M/P ratio not clinically relevant due to rapid metabolism. Considered compatible with breastfeeding.
Teratogenic Risk	Syntocinon (oxytocin) is not associated with teratogenic effects when used at standard doses for labor induction. However, prolonged high-dose exposure may cause fetal hypoxia, bradycardia, and neonatal hyperbilirubinemia. No trimester-specific malformation risk is established; uterine hyperstimulation risk is greatest during second and third trimester use.

Warnings & precautions

■ FDA Black Box Warning

NOT FOR ELECTIVE INDUCTION OF LABOR AT TERM DUE TO RISK OF UTERINE HYPERSTIMULATION, UTERINE RUPTURE, AND FETAL DISTRESS. SHOULD ONLY BE USED UNDER CONTINUOUS MEDICAL SUPERVISION WITH FETAL AND UTERINE MONITORING.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to oxytocin or any component","Cephalopelvic disproportion","Fetal distress where delivery is not imminent","Prolapsed umbilical cord","Placenta previa","Vasa previa","Contraindicated for elective induction in term pregnancies"]

Clinical Precautions

Precautions

["Uterine hyperstimulation and tetany","Uterine rupture, especially in grand multipara or with prior cesarean","Water intoxication and hyponatremia due to antidiuretic effect (high doses)","Fetal bradycardia, hypoxia, and neonatal jaundice","Hypotension and tachycardia with rapid IV administration"]

Clinical Tips & Counseling

Drug interactions

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SYNTOCINON

Clinical safety rating: caution

Comprehensive clinical and safety monograph for SYNTOCINON (SYNTOCINON).

How it works

What the body does with it

Metabolism	Rapidly metabolized in the liver and kidneys by oxytocinase (cysteine aminopeptidase) and other peptidases.
Excretion	Renal: >99% as intact oxytocin; biliary/fecal: negligible (<1%).
Half-life	Terminal elimination half-life: 1–6 minutes (intravenous); 1–9 minutes (intramuscular). Clinically, effects dissipate rapidly after infusion cessation.
Protein binding	Low (~30%); primarily binds to albumin and oxytocin-specific carrier proteins (e.g., neurophysin I).
Volume of Distribution	0.2–0.3 L/kg; reflects limited distribution into extracellular fluid and minimal tissue binding.
Bioavailability	Intramuscular: ~20–40% (due to rapid enzymatic degradation); Intravenous: 100%.
Onset of Action	Intravenous: 1–2 minutes; Intramuscular: 3–5 minutes.
Duration of Action	Intravenous: 15–60 minutes (dose-dependent); Intramuscular: 30–120 minutes. Uterine response wanes quickly after infusion stop.

Classification & Brands

Action Class	Uterotonic and abortificient
Brand Substitutes	Itocin 5IU Injection, Wotocin 5IU Injection, Indox 5IU Injection, Zygon 5IU Injection, Labtocin 5IU Injection

Dosing & administration

Dosage form	INJECTABLE
Renal impairment	No dosage adjustment required for renal impairment; oxytocin is rapidly metabolized and renally excreted, but no specific GFR-based guidelines exist.
Liver impairment	No dosage adjustment required for hepatic impairment; oxytocin is metabolized primarily by the liver, but no Child-Pugh based modifications have been established.
Pediatric use	Not indicated for pediatric use; safety and efficacy in children have not been established.
Geriatric use	Use with caution in elderly patients due to potential for uterine hyperstimulation and adverse cardiovascular effects; no specific dosage adjustments recommended.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for SYNTOCINON (SYNTOCINON).

Breastfeeding	Oxytocin is endogenous in breast milk; exogenous administration does not significantly increase milk levels. M/P ratio not clinically relevant due to rapid metabolism. Considered compatible with breastfeeding.
Teratogenic Risk	Syntocinon (oxytocin) is not associated with teratogenic effects when used at standard doses for labor induction. However, prolonged high-dose exposure may cause fetal hypoxia, bradycardia, and neonatal hyperbilirubinemia. No trimester-specific malformation risk is established; uterine hyperstimulation risk is greatest during second and third trimester use.