II. Indications
- Labor Induction or Labor Augmentation
- Prevention of Postpartum Hemorrhage
III. Mechanism
- Oxytocin is a hypothalamic polypetide stored in the posterior Pituitary Gland
- Oxytocin is encoded by the human OXT gene
- Oxytocin release is triggered by reflex response to Hypothalamus from infant sucking nipple
- Oxytocin acts to stimulate Smooth Muscle in the Uterus and in the Breast
- Increases force and frequency of uterine contractions
- Stimulates milk ejection in lactating women (contraction of alveolar myepithelium of the mammary glands)
- Oxytocin is similar in structure to the other posterior pituitary Hormone, Vasopressin (ADH)
- Oxytocin and Vasopressin differ by only 2 Amino Acid residues (out of 9 Amino Acids)
- Oxytocin may have Vasopressin-like effects (e.g. SIADH) with prolonged continuous infusion
IV. Medications
- Oxytocin 10 units/ml in 1 ml and 10 ml vials (multi-use)
V. Dosing: Labor Induction or Labor Augmentation
- See Labor Induction
- Precautions
- Use with a intravenous pump to maintain consistent and safe doses
- Continuous Fetal Monitoring
- Preparation: Oxytocin in Normal Saline Infusion
- Oxytocin 10 units in 1000 ml Normal Saline
- Starting rate of 6-12 ml/hour delivers 1-2 mU/minute
- Increasing rate 6 ml/hour delivers another 1 mU/min
- Oxytocin 20 units in 1000 ml Normal Saline
- Starting rate of 3-6 ml/hour delivers 1-2 mU/minute
- Increasing rate 3 ml/hour delivers another 1 mU/min
- Oxytocin 10 units in 1000 ml Normal Saline
- Protocol: Low Dose (preferred)
- Start: 0.5 to 2 mU/minute
- Increase: 1-2 mU/minute every 15-40 minutes
- Base Pitocin rate changes on contractions
- After 8 mU/minute, may then increase by 2 mIU/minute
- Maximum: 40 mU/minute
- Protocol: High Dose
- See Monitoring below
- Precautions
- Low dose protocol is preferred in all patients (see Labor Induction for efficacy)
- As of 2019, evidence is against the use of high dose Oxytocin (see Labor Induction for efficacy)
- Use only in Nulliparous patients only
- Protocol
- Start: 6 mU/minute
- Increase: 3-6 mU/minute every 15-40 minutes
- Maximum: 40-42 mU/minute
VI. Dosing: Postpartum Hemorrhage Management and Prophylaxis
-
Postpartum Hemorrhage prevention after Vaginal Delivery
- Oxytocin 10 units IM after delivery
- Oxytocin 10-40 units in 1 L IV fluid (NS, LR, D5W)
-
Postpartum Hemorrhage prevention after Cesarean Section
- High dose Oxytocin prevents uterine atony
- Dose: Oxytocin 2667 mU/min for 30 minutes
- Munn (2001) Obstet Gynecol 98:386-90 +PMID: 11530117 [PubMed]
VII. Adverse Effects
- Anaphylaxis
- Uterine hypertonicity
- Uterine tetanic contractions and Fetal Distress
- Uterine Rupture
-
Water Intoxication (SIADH)
- Associated with slow infusion >24 hours
VIII. Safety
- Avoid in Lactation
- In pregnancy, contraindicated, of course, prior to peripartum (at which point its primary use is pregnancy)
- Monitoring
- Continuous Fetal Monitoring
IX. Drug Interactions
-
Sympathomimetics
- Increased risk of Postpartum Hemorrhage when combined with Oxytocin
X. Pharmacokinetics: Intravenous Oxytocin
- Onset: 3 to 5 minutes
- Duration: 30 minutes (up to 2 to 3 hours)
- Half-Life: 3 to 5 minutes