Uterotonics
Key Points
- Uterotonics stimulate or increase uterine contractions — used for labor induction, augmentation, and postpartum hemorrhage (PPH) prevention
- Oxytocin (Pitocin): Prototype uterotonic; IV infusion starting at 1–2 mU/min; high-alert medication (ISMP) requiring continuous FHR and uterine monitoring
- Tachysystole (>5 contractions in 10 minutes): Immediately discontinue oxytocin → lateral position → IV fluid bolus 500 mL → terbutaline 0.25 mg SQ if needed
- Methylergonovine (Methergine): 0.2 mg IM/IV after delivery — contraindicated in hypertension and preeclampsia
- Misoprostol (Cytotec): Prostaglandin E1; CANNOT be removed once administered — plan carefully before use
- Dinoprostone (Cervidil/Prepidil): Prostaglandin E2; vaginal insert CAN be removed; requires refrigeration
Drug Class Overview
Uterotonic drugs increase uterine smooth muscle tone and contractility. Indications include induction of labor, augmentation of a stalled labor pattern, cervical ripening, and prevention or treatment of postpartum hemorrhage (PPH). These medications are administered in acute care settings with continuous monitoring equipment. Because of their potential for life-threatening uterine and fetal complications, all uterotonic agents are classified as high-alert medications.
Oxytocin (Pitocin)
Mechanism: Exerts selective action on uterine smooth musculature → stimulates rhythmic contractions, increases frequency of existing contractions, and raises uterine muscle tone.
Routes and Dosing:
| Indication | Route | Dose |
|---|---|---|
| Labor induction/augmentation | IV continuous infusion | Start ≤1–2 mU/min; increase ≤1–2 mU/min q15–30 min to achieve normal labor pattern |
| PPH prevention (after placenta delivery) | IV continuous infusion | 10–40 units added to 1000 mL isotonic solution; rate adjusted to control uterine atony |
| PPH prevention | IM | 10 units (1 mL) after placenta delivery |
Half-life: 3–5 minutes — rapid effect allows immediate dose titration and quick offset if discontinued.
Contraindications: Hypersensitivity; obstetric emergencies negatively affecting birthing parent or fetus; fetal distress; unfavorable fetal presentation; when vaginal delivery is inadvisable; uterine contraction pattern dysfunction.
Adverse Effects:
- Birthing parent: Nausea, vomiting, cardiac dysrhythmias, uterine hypertonicity, uterine rupture, PPH, pelvic hematoma, water intoxication, dilutional hyponatremia (oxytocin has antidiuretic properties)
- Fetus: Bradycardia, cardiac dysrhythmias, impaired oxygenation, permanent CNS damage, retinal hemorrhage
Tachysystole Response Protocol
Tachysystole = >5 uterine contractions in 10 minutes or contractions lasting >2 minutes
- Discontinue oxytocin immediately
- Reposition to left lateral (increases uterine blood flow, relieves aortocaval compression)
- Administer IV fluid bolus (500 mL isotonic solution)
- Increase supplemental oxygen to 8–10 L/min via face mask
- If no improvement: Terbutaline 0.25 mg subcutaneous (tocolytic to relax uterus)
- Notify provider; continuous FHR monitoring for late decelerations
Methylergonovine (Methergine)
Mechanism: Acts directly on uterine smooth muscle to produce sustained tetanic contraction → prevents PPH and promotes uterine involution.
Route/Dose: 0.2 mg (1 mL) IM or IV; IV administration must be over ≥60 seconds; may repeat q2–4 hours as needed.
Timing: After delivery of the anterior shoulder, after delivery of the placenta, or during the postpartum period.
Contraindications: Pregnancy (except at delivery), hypertension, toxemia/preeclampsia, coronary artery disease — methylergonovine causes vasoconstriction and can dramatically increase blood pressure.
Drug-Food Interaction: Grapefruit and grapefruit juice (CYP3A4 inhibition → increased drug levels).
Cervical Ripening Agents (Prostaglandins)
Prostaglandins soften and dilate the cervix (cervical ripening) and stimulate uterine contractions. Used when cervix is unfavorable (low Bishop score) for induction.
Misoprostol (Cytotec) — Prostaglandin E1
| Feature | Detail |
|---|---|
| Route/Dose | Oral: 50 mcg q4–6h; vaginal: 25–50 mcg q4–6h |
| Removal | CANNOT be removed once administered orally or vaginally |
| Cost | Inexpensive; does not require refrigeration |
| Warning | FDA Black Box Warning — can cause uterine rupture, especially with prior uterine surgery |
Dinoprostone (Cervidil/Prepidil) — Prostaglandin E2
| Feature | Detail |
|---|---|
| Cervidil | 10 mg vaginal insert; left in place up to 12 hours |
| Prepidil | 0.5 mg vaginal gel; may repeat q6h × 2 additional doses max |
| Removal | CAN be removed — pull string if tachysystole or fetal distress occurs |
| Storage | Requires refrigeration |
| Cost | More expensive than misoprostol |
Nursing Assessment and Monitoring
Before Administration:
- Verify gestational age, Bishop score, fetal presentation, and contraindications
- Confirm continuous electronic fetal monitoring (EFM) is applied — oxytocin requires continuous FHR and uterine activity monitoring
- Perform independent double-check (high-alert medication protocol)
- Review for prior uterine surgery (increases rupture risk with prostaglandins)
During Oxytocin Administration:
- Assess contraction frequency, duration, intensity, and resting tone continuously
- Monitor FHR for decelerations with each contraction (late decelerations = uteroplacental insufficiency)
- Titrate dose based on labor progress and contraction pattern per institutional protocol
- Monitor maternal vital signs, urine output (water intoxication risk), and IV site
Patient Education:
- Explain each medication’s purpose and expected effects before administration
- Describe how contractions will feel and when to report changes
- For postpartum oxytocin or methylergonovine: instruct on fundal assessment, lochia monitoring, and reporting heavy bleeding
Related Concepts
- nursing-care-during-the-first-stage-of-labor — Labor monitoring context and contraction assessment
- postpartum-hemorrhage — Uterotonics are first-line treatment for PPH from uterine atony
- fhr-and-uc-intervention-framework — FHR response patterns and interventions with oxytocin
- tocolytics — Medications that counteract uterotonic effects (terbutaline, magnesium sulfate)
- labor-analgesics — Pharmacological pain management during induced or augmented labor
- high-alert-medications — Oxytocin classification as ISMP high-alert medication
Self-Check
- A nurse is administering oxytocin for labor augmentation. The EFM shows 6 contractions in 10 minutes, with the last contraction lasting 3 minutes. The FHR shows late decelerations. In order, what nursing actions are required?
- The provider orders methylergonovine 0.2 mg IV push for a postpartum patient. The patient’s BP is 158/98. What should the nurse do before administering?
- A patient at 39 weeks received misoprostol vaginally 30 minutes ago and is now experiencing uterine hyperstimulation. The nurse prepares to remove the misoprostol insert. Is this possible? Why or why not?