Oxytocin

Also known as: OT, Pitocin, Syntocinon

Evidence: Clinical

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Overview

Posterior-pituitary nonapeptide hormone; IV or IM oxytocin (Pitocin and generics) is approved by the FDA for labor induction and postpartum bleeding. Intranasal social-behavior results are mixed.

Oxytocin is a nine-residue hypothalamic hormone released from the posterior pituitary. Synthetic oxytocin injection (Pitocin, NDA 018261, and several generics) is marketed in the US for intravenous induction or augmentation of labor with a medical indication and for intravenous or intramuscular control of postpartum bleeding; the label excludes elective induction. The only US intranasal product, Syntocinon nasal spray (NDA 012285), is discontinued. Intranasal research grew from small experiments such as increased trust in an investment game (Kosfeld 2005), but the largest trial, 290 children with autism over 24 weeks, found no improvement in social withdrawal (Sikich 2021).

Benefits

Uterine contraction for medically indicated labor induction and postpartum bleeding (FDA-labeled, IV/IM), increased trust in an economic game (single small human study), no effect on social withdrawal in autism (RCT, n=290)

Dosing reference

Research dose: Community range 10 to 50 IU intranasal; research studies used 24 to 40 IU single doses. Obstetric IV/IM use follows the Pitocin label.
Reconstitution: 2 mL bacteriostatic water
Common vial sizes: 5 mg

Research intranasal studies typically use 24-40 IU as a single dose. Contraindicated in pregnancy outside obstetric supervision (uterine contractions). Repeated or high parenteral dosing carries hyponatremia/water-intoxication risk; can blunt blood pressure and cause flushing. Behavioral effects in trials are small and context-dependent.

Mechanism

Oxytocin acts on oxytocin receptors in the myometrium and raises intracellular calcium, driving actomyosin contraction through myosin light-chain kinase; receptor density rises sharply in pregnancy and peaks in early labor at term, so the uterine response varies widely between patients (Pitocin label). It differs from vasopressin at two of eight residues, which explains its pressor and antidiuretic effects at large doses (Pitocin label). Plasma oxytocin during infusion was measured against spontaneous labor (Fuchs 1983; Seitchik 1984). Central effects on social behavior are proposed from receptor distribution and intranasal studies in humans, with inconsistent results (Heinrichs 2009; Sikich 2021).

Evidence

Clinical: at least one published human trial or an approved drug

Oxytocin infusion for dysfunctional labor: clinical outcomes of augmentation (Seitchik and Castillo, 1982)
Plasma oxytocin pharmacokinetics measured during labor augmentation, the basis of the label's low starting infusion rate (Seitchik et al., 1984)
Plasma oxytocin in spontaneous versus oxytocin-induced labor at term; the label states infusion up to 6 mU/min matches spontaneous-labor levels (Fuchs et al., 1983)
A single intranasal dose increased trust in an investment game in healthy men (Kosfeld et al., 2005)
Intranasal oxytocin daily for 24 weeks in 290 children and adolescents with autism did not improve social withdrawal versus placebo (Sikich et al., 2021)
Human-trial status: injectable oxytocin is approved by the FDA and marketed for obstetric use; no intranasal product is approved in the US (Syntocinon nasal spray discontinued), and intranasal social-cognition findings have not held up in the largest RCT

References

Side effects

Pitocin label, maternal: anaphylaxis, nausea, vomiting, cardiac arrhythmia and premature ventricular contractions, hypertensive episodes, subarachnoid hemorrhage, postpartum hemorrhage, pelvic hematoma, fatal afibrinogenemia and uterine rupture. Excess dose causes uterine hypertonicity or tetanic contraction. Slow infusion over 24 hours has caused severe water intoxication with seizures, coma and death, from its antidiuretic effect. Fetal or neonatal: bradycardia, arrhythmia, low Apgar scores, jaundice, retinal hemorrhage, seizures, brain damage and death.

Storage

Storage: Refrigerate 2-8°C (36-46°F)
Lyophilized: 2+ years at room temp, 3+ years refrigerated
Reconstituted: 28-30 days refrigerated

Pharmacology

Half-life: Plasma 1 to 6 min (human, IV), shorter in late pregnancy and lactation; uterine response fades within 1 h after IV, lasts 2 to 3 h after IM (Pitocin label)
Bioavailability: Approved routes are IV infusion and IM injection; oxytocin distributes through extracellular fluid and small amounts probably reach the fetus (Pitocin label). No US intranasal product exists, and no label gives an intranasal or CNS figure.
Molecular weight: 1007.19 Da
Sequence: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (disulfide bridge Cys1-Cys6)