Oxytocin is a nonapeptide hormone (C43H66N12O12S2) secreted by the posterior pituitary gland. The synthetic version is identical to the endogenous hormone. In the Indian clinical context, it is a critical uterotonic agent used primarily for the induction and augmentation of labor, management of postpartum hemorrhage (PPH), and post-abortion hemorrhage. It is considered a first-line agent for active management of the third stage of labor (AMTSL) as per WHO and FOGSI guidelines. Its effects are rapid but short-lived, making it suitable for controlled administration.
Adult: **Induction/Augmentation of Labor:** IV infusion is the ONLY recommended route. Start at 1-2 mIU/min (0.001-0.002 IU/min). Increase by 1-2 mIU/min every 30-60 minutes until adequate contraction pattern is established (3-5 contractions per 10 minutes). Maximum dose rarely exceeds 20 mIU/min. **Postpartum Hemorrhage (PPH) Prophylaxis:** 5-10 IU IM or by slow IV injection after delivery of the anterior shoulder or after the baby. **PPH Treatment:** 10-40 IU in 500-1000 mL IV fluid (e.g., Normal Saline or Ringer's Lactate) infused at a rate sufficient to control uterine atony. Alternatively, 10 IU IM. May be repeated. **Incomplete/Inevitable Abortion:** 10 IU IV in 500 mL IV fluid infused at 10-20 mIU/min.
Note: **CRITICAL:** NEVER administer undiluted as an IV bolus. For IV infusion, always use an infusion pump for precise control. Dilute in an isotonic IV solution like Normal Saline or Ringer's Lactate. Protect infusion from light. For IM use, administer deep into a large muscle mass. A dedicated IV line is preferred; if using a Y-site, flush line before and after. Incompatible with fibrinolytics, diazepam, sodium bicarbonate, fat emulsions, and several other drugs.
Oxytocin binds to specific G-protein coupled oxytocin receptors (OXTR) located on the myometrial (uterine) smooth muscle cells and myoepithelial cells of the breast. In the uterus, receptor activation triggers a phosphatidylinositol-calcium second messenger system, leading to an influx of extracellular calcium and release of intracellular calcium stores. This results in increased frequency and force of uterine contractions. It also promotes contraction of the myoepithelial cells surrounding the mammary alveoli, facilitating milk ejection (let-down reflex). At high doses, it possesses weak antidiuretic activity by activating renal V2 receptors.
Pregnancy: **Category:** Not formally classified by US FDA. Used specifically during pregnancy for induction/augmentation of labor. Benefit-risk assessment is critical. Contraindicated in situations where vaginal delivery is not advised.
Driving: Not applicable as used in controlled hospital settings.
| Vasopressors (e.g., Epinephrine, Phenylephrine) | Oxytocin may cause transient hypotension; concomitant use with vasopressors can lead to severe hypertension. A 3-4 hour interval is recommended. | Major |
| Cyclopropane Anesthesia | Increased risk of maternal sinus bradycardia and abnormal AV rhythms. Now historical, but caution with halogenated hydrocarbon anesthetics remains. | Moderate |
| Other Uterotonics (e.g., Methylergometrine, Carboprost) | Potentiates uterine contraction, increasing risk of hyperstimulation and rupture. Used sequentially in PPH, not concurrently for induction. | Major |
| Sympathomimetics (e.g., Ritodrine, Salbutamol - used as tocolytics) | Antagonistic effect on uterine activity. | Moderate |