What are examples of uterotonic agents?

Examples of Uterotonic Agents

Uterotonic agents are drugs that stimulate uterine contractions and are primarily used for the prevention and treatment of postpartum hemorrhage, as well as for labor induction and augmentation. The main classes include oxytocin, ergot alkaloids, prostaglandins, and synthetic analogues.

First-Line Uterotonic Agent

• Oxytocin: The first-choice uterotonic for both prevention and treatment of postpartum hemorrhage 1, 2, 3
  • Administered as 5-10 IU via slow IV or intramuscular injection immediately postpartum 4
  • Acts directly on uterine smooth muscle to increase tone, rate, and amplitude of contractions 1
  • Onset of action: immediate (IV), 2-5 minutes (IM), 5-10 minutes (oral) 1
  • Has intrinsic antidiuretic effect that may increase risk of water intoxication when given continuously 1

Second-Line Uterotonic Agents

• Ergot Alkaloids:

  • Methylergonovine (Methergine): Acts directly on smooth muscle of the uterus 5, 2
    • Induces rapid and sustained tetanic uterotonic effect 5
    • Bioavailability: ~60% oral, ~78% intramuscular during delivery 5
    • Contraindicated in patients with respiratory diseases due to risk of bronchospasm 4
    • Common second-line agent when oxytocin is ineffective 3, 6

• Prostaglandins:

  • Carboprost (PGF2α): First-line prostaglandin for PPH treatment despite side effects 2, 6
    • Effective for refractory uterine atony 6
    • Should be avoided in women with asthma as it may cause bronchoconstriction 4
  • Misoprostol: Alternative when oxytocin is unavailable 2, 3
    • Less effective than oxytocin but useful in resource-limited settings 3, 7

• Carbetocin: Synthetic oxytocin analogue 2, 3

  • Should be used instead of continuous oxytocin infusion in elective cesarean sections 3
  • Reduces need for additional uterotonic agents 3

Clinical Effectiveness Comparison

• Recent randomized controlled trial showed no significant difference in uterine tone scores between methylergonovine and carboprost for treating refractory uterine atony during cesarean delivery, indicating either agent is acceptable as a second-line treatment 6
• Mean uterine tone scores 10 minutes after administration were 7.3±1.7 for methylergonovine and 7.6±2.1 for carboprost 6

Common Indications for Uterotonics

• Prevention of postpartum hemorrhage: Active management of third stage of labor 4, 2
• Treatment of uterine atony: Primary cause of postpartum hemorrhage 2, 7
• Labor induction and augmentation: Primarily with oxytocin 8
• Cervical ripening: Mainly prostaglandins, but oxytocin has also been used 8

Important Considerations and Cautions

• Careful titration of uterotonics is essential to avoid uterine hyperstimulation 9
• Injudicious use of uterotonics to augment weak contractions is a risk factor for uterine rupture 9
• Oxytocin should be avoided in cases of cephalopelvic disproportion (CPD) 9
• Active management with uterotonics enhances uterine contraction and promotes placental separation, reducing bleeding risk 4
• Careful attention should be paid to minimizing trauma when administering uterotonics to women receiving anticoagulants 9, 4

Uterotonic agents play a critical role in modern obstetric practice, particularly in preventing and treating postpartum hemorrhage, which remains a major cause of maternal mortality worldwide. The choice of agent should be based on clinical scenario, availability, contraindications, and institutional protocols.