Introduction
Oxytocin is a peptide hormone and neuropeptide that plays crucial roles in childbirth, breastfeeding, and social bonding. Synthetically produced oxytocin is widely used in obstetric practice to induce or augment labor and to control postpartum hemorrhage. Beyond its reproductive functions, oxytocin has gained attention for its potential roles in social behavior, anxiety regulation, and emotional bonding, though these applications remain primarily investigational.
Mechanism of Action
Oxytocin acts as a potent stimulant of uterine smooth muscle contraction through specific oxytocin receptors in the myometrium. The drug increases the frequency and force of uterine contractions, particularly in the term pregnant uterus. Oxytocin also stimulates milk ejection by causing contraction of myoepithelial cells in mammary gland alveoli. The hormone binds to G-protein coupled receptors, activating phospholipase C and increasing intracellular calcium concentrations, which triggers smooth muscle contraction.
Indications
- Induction of labor in patients with medical indications for labor initiation
- Augmentation of dysfunctional labor patterns
- Control of postpartum uterine hemorrhage
- Completion of incomplete or inevitable abortion
- Uterine stimulation during cesarean section
- Management of uterine atony
- adjunct therapy in severe postpartum hemorrhage
Dosage and Administration
Labor induction/augmentation:- Initial dose: 0.5-2 mU/min IV infusion
- Titrate: Increase by 1-2 mU/min every 30-60 minutes
- Maximum dose: 20-40 mU/min
- 10-40 units in 1000 mL IV fluid at rate sufficient to control uterine atony
- Alternatively: 10 units IM after delivery of placenta
- 10 units IV in 500 mL normal saline at 20-40 drops/minute
- Renal impairment: Use with caution; no specific dosage adjustment
- Hepatic impairment: Use with caution
- Elderly: Not typically used in this population
Pharmacokinetics
Absorption: IV administration provides immediate onset; IM administration onset within 3-5 minutes Distribution: Distributed throughout extracellular fluid; minimal protein binding Metabolism: Primarily metabolized in liver and kidneys by oxytocinases Elimination: Plasma half-life 1-6 minutes; eliminated via kidney and liver Duration: Uterine response begins within 3-5 minutes IV and persists for 2-3 hoursContraindications
- Hypersensitivity to oxytocin or any component of formulation
- Significant cephalopelvic disproportion
- Unfavorable fetal positions or presentations
- Obstetric emergencies where benefit-to-risk ratio favors surgery
- Hypertonic uterine patterns
- Fetal distress where delivery is not imminent
- Severe cardiovascular disease
- Conditions where vaginal delivery is contraindicated
Warnings and Precautions
- Uterine hyperstimulation: May occur even with proper administration
- Water intoxication: With prolonged IV infusion and excessive fluid volume
- Cardiovascular effects: Transient hypotension, tachycardia, arrhythmias
- Uterine rupture: Risk increased with high doses, multiparity, or uterine surgery history
- Fetal effects: Bradycardia, hypoxia, CNS damage, neonatal jaundice
- Use with caution in: Patients with predisposing factors for uterine rupture
- Continuous fetal monitoring required during administration
Drug Interactions
- Vasoconstrictors: May cause severe hypertension
- Cyclopropane anesthesia: May cause hypotension and bradycardia
- Other oxytocics: Additive effects requiring dose reduction
- Sympathomimetic pressor amines: Potentiated pressor effects
- Caudal block anesthesia: Enhanced hypotensive effects
Adverse Effects
Maternal:- Uterine hypertonicity (10-15%)
- Nausea, vomiting (5-10%)
- Cardiac arrhythmias (2-5%)
- Hypotension/hypertension (1-3%)
- Water intoxication with seizures (rare)
- Uterine rupture (rare)
- Postpartum hemorrhage (1-2%)
- Fetal bradycardia (10-20%)
- Neonatal jaundice (5-10%)
- Low Apgar scores (2-5%)
- Neonatal retinal hemorrhage (rare)
- Permanent CNS or brain damage (rare)
Monitoring Parameters
- Uterine activity: Frequency, duration, and force of contractions
- Fetal heart rate: Continuous electronic monitoring
- Maternal vital signs: Blood pressure, pulse, respiratory rate every 15-30 minutes
- Fluid balance: Input and output to prevent water intoxication
- Labor progress: Cervical dilation, fetal station, and presentation
- Postpartum: Uterine tone and vaginal bleeding
- Electrolytes: With prolonged high-dose infusion
Patient Education
- Purpose of medication and expected effects
- Importance of continuous fetal monitoring
- Report immediately any severe abdominal pain, difficulty breathing, or chest pain
- Understand signs of water intoxication: headache, nausea, vomiting
- Postpartum: Report excessive bleeding or passage of large clots
- Breastfeeding: Oxytocin may facilitate milk let-down reflex
- Potential side effects and when to seek medical attention
References
1. American College of Obstetricians and Gynecologists. (2020). Practice Bulletin No. 228: Labor Induction. Obstetrics & Gynecology, 135(6), e210-e227. 2. World Health Organization. (2018). WHO recommendations: uterotonics for the prevention of postpartum haemorrhage. 3. Goodwin, T. M., & Zografyan, A. (2019). Oxytocin: the hormone of love and labor. Journal of Clinical Endocrinology & Metabolism, 104(10), 1-12. 4. Drug Facts and Comparisons. (2023). Oxytocin monograph. Wolters Kluwer. 5. Simpson, K. R., & James, D. C. (2020). Effects of oxytocin-induced uterine hyperstimulation during labor on fetal oxygen status and fetal heart rate patterns. American Journal of Obstetrics and Gynecology, 217(3), 346-e1. 6. King, T. L., & Brucker, M. C. (2021). Pharmacology for Women's Health. Jones & Bartlett Learning. 7. UpToDate. (2023). Oxytocin drug information. Wolters Kluwer. 8. National Institute for Health and Care Excellence. (2021). Intrapartum care for healthy women and babies. NICE guideline CG190.