Summary

The combination of oxytocin and ergometrine can cause severe uterine tetany and cervical lacerations due to their synergistic effects on uterine contractions. This interaction is considered contraindicated and requires careful timing and monitoring when both drugs are used in obstetric care.

Introduction

Oxytocin is a synthetic hormone that stimulates uterine contractions and is commonly used for labor induction, augmentation, and postpartum hemorrhage control. Ergometrine (methylergonovine) is an ergot alkaloid that causes sustained uterine contractions and is primarily used for the prevention and treatment of postpartum hemorrhage. Both medications belong to the class of oxytocic agents and are essential tools in obstetric practice.

Mechanism of Interaction

The interaction between oxytocin and ergometrine occurs through their complementary mechanisms of action on uterine smooth muscle. Oxytocin binds to oxytocin receptors in the myometrium, causing rhythmic contractions through calcium influx. Ergometrine acts on alpha-adrenergic and serotonin receptors, producing sustained, tetanic uterine contractions. When used simultaneously, these drugs create additive effects that can result in excessive uterine contractility, leading to uterine tetany, entrapment of the placenta, and potential uterine rupture.

Risks and Symptoms

The primary clinical risks of combining oxytocin and ergometrine include severe uterine tetany, cervical and vaginal lacerations, retained placenta due to cervical spasm, uterine rupture, and increased risk of postpartum hemorrhage paradoxically. The sustained contractions can also compromise fetal blood supply if administered before complete delivery of the baby and placenta. Additional risks include hypertension, particularly in patients with pre-existing cardiovascular conditions, as ergometrine can cause significant vasoconstriction.

Management and Precautions

The key management principle is to avoid simultaneous administration of oxytocin and ergometrine. Ergometrine should only be given after complete delivery of the placenta and when the cervix is fully dilated. If oxytocin is being used for labor augmentation, it should be discontinued before ergometrine administration. When both drugs are needed for postpartum hemorrhage management, allow adequate time between administrations and monitor uterine tone carefully. Healthcare providers should have emergency protocols in place for managing uterine tetany, including immediate discontinuation of oxytocic agents, uterine relaxants (such as terbutaline), and surgical intervention if necessary.