Usage
- Medical Conditions: Oxytocin is prescribed for labor induction, augmentation of labor, control of postpartum bleeding (prevention and treatment), and incomplete or inevitable abortion. It is also used to assist in milk letdown.
- Pharmacological Classification: Uterotonic Agent, Hormone
- Mechanism of Action: Oxytocin stimulates contraction of the uterine smooth muscle by increasing intracellular calcium levels, which enhances the formation of actomyosin, the contractile protein. It binds to specific myometrial receptors, the concentration of which increases during pregnancy.
Alternate Names
- International/Regional Variations: Syntocinon, Pitocin
- Brand Names: Pitocin
How It Works
- Pharmacodynamics: Oxytocin causes rhythmic contractions of the uterine smooth muscle, similar to those seen in spontaneous labor. It has mild antidiuretic properties similar to vasopressin.
- Pharmacokinetics:
- Absorption: Administered intravenously (IV) or intramuscularly (IM). IV administration results in almost immediate uterine response, while IM injection has an onset within 3-5 minutes.
- Metabolism: Primarily metabolized in the liver and kidneys by oxytocinase.
- Elimination: Metabolites are excreted in the urine. Less than 1% is excreted unchanged in the urine. Plasma half-life is 1 to 6 minutes, shorter during late pregnancy and lactation.
- Mode of Action: Binds to oxytocin receptors in the myometrium, activating phospholipase C, which increases intracellular calcium levels, leading to uterine muscle contraction.
- Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Binds to G protein-coupled oxytocin receptors, leading to increased intracellular calcium via inositol trisphosphate pathway.
- Elimination Pathways: Renal and hepatic metabolism and excretion.
Dosage
Standard Dosage
Adults:
- Labor Induction/Augmentation: Initial dose of 0.5-1 milliunits/min (3-6 mL/hour of a 10 milliunits/mL solution) IV. Increase by 1-2 milliunits/min every 30-60 minutes until desired contraction pattern is established. After reaching active labor (5-6 cm dilation), the dose may be reduced. Maximum dose is generally 20 milliunits/min, may go up to 40 milliunits/min in certain cases.
- Postpartum Bleeding (Prevention): 10 units IM after placental delivery, or 5 units slow IV push over 5 minutes, or 5-10 IU by i.v. infusion (5 IU diluted in physiological electrolyte solution and administered as an i.v. drip infusion over 5 minutes).
- Postpartum Bleeding (Treatment): 10-40 units in 500-1000 mL IV solution infused at a rate to control uterine atony.
- Incomplete/Inevitable Abortion: 10-20 milliunits/min IV infusion; not to exceed 30 units in a 12-hour period.
Children: No established pediatric dosing guidelines.
Special Cases:
- Elderly Patients: Limited data; use with caution.
- Patients with Renal Impairment: No specific dosage adjustments; use with caution due to potential for accumulation and prolonged action.
- Patients with Hepatic Dysfunction: No specific dosage adjustments are typically necessary.
- Patients with Comorbid Conditions: Use with caution in patients with cardiovascular disease or pre-eclampsia.
Clinical Use Cases
Dosing guidelines provided above cover typical clinical use cases.
Dosage Adjustments
Individualize dose based on uterine response and maternal/fetal status.
Side Effects
Common Side Effects:
- Nausea
- Vomiting
- Headache
- Sinus pain/irritation
- Runny nose
- Memory Problems
Rare but Serious Side Effects:
- Uterine rupture
- Water intoxication
- Fetal distress
- Hypotension
- Tachycardia
- Cardiac arrhythmias
- Postpartum hemorrhage
Long-Term Effects: No significant long-term effects reported.
Adverse Drug Reactions (ADR):
- Anaphylaxis
- Uterine hyperstimulation
- Fetal bradycardia
Contraindications
- Fetal distress where delivery is not imminent
- Cephalopelvic disproportion
- Malpresentation of the fetus
- Hypersensitivity to oxytocin
- Conditions where vaginal delivery is contraindicated (e.g., placenta previa, vasa previa, cord prolapse)
- Hypertonic uterus
Drug Interactions
- Prochlorperazine: May lead to severe persistent hypertension
- Caudal anesthetics with vasoconstrictors: May cause severe persistent hypertension
- Warfarin: unknown
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Not formally categorized, but considered acceptable for use when medically necessary.
- Fetal Risks: Fetal distress, bradycardia, low Apgar scores, jaundice, seizures, death.
- Breastfeeding: Oxytocin may be given to induce milk letdown; endogenous oxytocin is present in breast milk.
Drug Profile Summary
- Mechanism of Action: Stimulates uterine smooth muscle contraction.
- Side Effects: Nausea, vomiting, headache, uterine rupture, water intoxication.
- Contraindications: Fetal distress, cephalopelvic disproportion, hypersensitivity.
- Drug Interactions: Prochlorperazine, vasoconstrictors, warfarin.
- Pregnancy & Breastfeeding: Use with caution; potential fetal risks; present in breast milk.
- Dosage: Highly individualized based on uterine response; see above.
- Monitoring Parameters: Uterine contractions, fetal heart rate, maternal blood pressure and heart rate.
Popular Combinations
Often used alone. May be combined with other uterotonics if necessary.
Precautions
- General Precautions: Monitor maternal and fetal status closely during administration. Discontinue if hyperstimulation occurs.
- Specific Populations: Use with caution in patients with cardiovascular disease or renal impairment.
- Lifestyle Considerations: No relevant lifestyle considerations.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Oxytocin?
A: The dosage is highly individualized based on uterine response. For labor induction/augmentation, the initial dose is 0.5-1 milliunits/min IV, increased gradually until desired contraction pattern is achieved. For postpartum bleeding, 10 units IM or 10-40 units in IV solution. For incomplete/inevitable abortion, 10-20 milliunits/min IV.
Q2: How is Oxytocin administered?
A: Oxytocin is administered via IV infusion or IM injection. IV infusion is preferred for labor induction and augmentation.
Q3: What are the common side effects of Oxytocin?
A: Common side effects include nausea, vomiting, headache.
Q4: What are the serious side effects of Oxytocin?
A: Serious side effects include uterine rupture, water intoxication, fetal distress, and cardiac arrhythmias.
Q5: What are the contraindications to using Oxytocin?
A: Contraindications include fetal distress where delivery is not imminent, cephalopelvic disproportion, hypersensitivity, and conditions where vaginal delivery is unsafe.
Q6: What are the key monitoring parameters during Oxytocin administration?
A: Monitor uterine contractions, fetal heart rate, and maternal blood pressure and heart rate.
Q7: Can Oxytocin be used during breastfeeding?
A: Oxytocin is present in breast milk and can be used to stimulate milk letdown.
Q8: How should Oxytocin be administered for postpartum hemorrhage?
A: Administer 10 units IM after placental delivery or 10-40 units by IV infusion, adjusting the rate to control bleeding.
Q9: Can Oxytocin be used for incomplete abortion?
A: Yes, 10-20 milliunits/min by IV infusion, not to exceed 30 units in a 12-hour period.
Q10: What should be done if uterine hyperstimulation occurs during Oxytocin administration?
A: Immediately discontinue the oxytocin infusion and administer oxygen to the mother. Evaluate both mother and fetus for signs of distress.
