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 also used to stimulate milk ejection (let-down reflex) in lactation. Its action is rapid, potent, and specific to uterine and mammary tissue.
Adult: **Induction/Augmentation of Labor:** IV infusion is the ONLY recommended method. Initial dose: 1-2 mIU/min (0.001-0.002 IU/min). Increase by 1-2 mIU/min at 30-60 minute intervals until a physiologic contraction pattern is established (3-5 contractions per 10 minutes). Typical maximum dose: 20 mIU/min. **Postpartum Hemorrhage (PPH) Prevention/Management:** IV: 10-40 IU in 1 liter of IV fluid at a rate to control uterine atony. IM: 5-10 IU (commonly 5IU) after delivery of the anterior shoulder or after placental delivery. **Incomplete Abortion:** IV infusion: 10-20 units in 500 mL IV fluid at 20-40 drops/min.
Note: **For IV Infusion:** MUST be diluted in an isotonic IV solution (e.g., Normal Saline, Ringer's Lactate). Use an infusion pump for precise control. Never give as an undiluted IV bolus, as it can cause severe hypotension and cardiac arrhythmias. **For IM:** Administer deep intramuscularly into the gluteal or deltoid muscle. **Storage:** Unopened vials must be refrigerated (2-8°C). Protect from light. Do not use if solution is cloudy or contains particles. Diluted solutions should be used immediately.
Oxytocin acts on specific G-protein coupled oxytocin receptors (OXTR) concentrated in the myometrium of the pregnant uterus and the myoepithelial cells surrounding the alveoli of the mammary gland. Receptor activation triggers the phosphatidylinositol-calcium second messenger system, leading to a rapid increase in intracellular calcium ions (Ca2+). In the uterus, this causes rhythmic contractions of uterine smooth muscle. The sensitivity of the uterus to oxytocin increases dramatically during pregnancy, peaking at term. In the breast, contraction of myoepithelial cells forces milk from the alveoli into the lactiferous ducts (milk let-down). It also has weak antidiuretic and vasopressor activity due to structural similarity to vasopressin.
Pregnancy: **Category:** Not formally classified under the FDA pregnancy categories, but is used during pregnancy for labor induction/augmentation. Use is restricted to the indication and requires careful fetal monitoring. Contraindicated in situations where vaginal delivery is not advised.
Driving: Not relevant, as administered in a controlled hospital setting.
| Vasopressors (e.g., Epinephrine, Phenylephrine) | Potentiated hypertensive effect; severe hypertension and postpartum cerebral hemorrhage risk. | Major |
| Cyclopropane Anesthesia | Increased risk of arrhythmias, including sinus bradycardia and atrioventricular nodal rhythm. (Less relevant with modern anesthesia). | Major |
| Other Uterotonics (e.g., Methylergometrine, Carboprost, Misoprostol) | Additive/synergistic effect leading to uterine hyperstimulation and rupture. | Major |
| Sympathomimetics (e.g., Ritodrine, Salbutamol - Tocolytic agents) | Antagonistic effect; ritodrine inhibits oxytocin-induced contractions. | Moderate |
| Thiopental Sodium | May potentiate pressor effects of oxytocin. | Moderate |
Same composition (Oxytocin (5IU)), different brands: