Mechanism of Action and Pharmacodynamics
The drug is a natural alkaloid. At the molecular level, ergometrine acts as an agonist of $5-HT_{2A}$ receptors (serotonin receptors).
The key difference between ergometrine and oxytocin (a native neurohypophysial hormone) lies in their effects on the myometrium. While oxytocin at physiological concentrations stimulates normal rhythmic labor contractions, ergot alkaloids induce a sustained tonic contraction of the uterus. These are not physiological contractions, but rather a prolonged, continuous spasm of the smooth muscle.
In addition, the drug affects endocrine regulation: it suppresses prolactin secretion, which naturally leads to the inhibition of breast milk production (decreased lactation).
Clinical Application and Biomechanics of Hemostasis
The main goal of administering ergometrine is to stop bleeding. It is important to understand the pathogenetic rationale: the drug does not increase blood clotting and does not directly affect coagulation factors.
Its hemostatic effect is exclusively biomechanical in nature. The powerful tonic contraction of the myometrium causes the muscle fibers to physically (mechanically) compress the gaping blood vessels of the uterus.
Main Indications:
- Treatment of uterine atony and hemorrhage in the early postpartum period.
- Bleeding following surgical abortion.
- Uterine bleeding in non-pregnant patients.
- Reduction of uterine tone after delivery.
Contraindications and Adverse Effects
The drug is strictly contraindicated during pregnancy and labor prior to the complete delivery of the placenta.
Why can ergometrine not be used for labor induction? Due to the sharp increase in basal myometrial tone, uteroplacental blood flow is severely impaired. This creates a high risk of acute fetal hypoxia. To augment labor, oxytocin, pituitrin, or dinoprost are used, but under no circumstances ergot alkaloids.
It should also be remembered that tocolytics (atosiban, salbutamol, magnesium sulfate) are contraindicated in atonic postpartum hemorrhage. They relax the uterus and would only worsen blood loss.
Adverse Effects:
- CNS: headache, vivid hallucinations.
- GI: nausea, vomiting, diarrhea, abdominal pain.
In overdose or ergot poisoning, ergotism develops. In addition to hallucinations and dyspepsia, it is characterized by persistent peripheral vasospasm of the extremities with endothelial damage, which in severe cases leads to gangrene.
Formulations and Administration
The drug is available in enteral and parenteral formulations. Dosages are extremely small, so care must be taken with decimal places when prescribing.
- Tablets: 0.2 mg.
- Solution in ampoules: 0.02%, volume 0.5 mL and 1 mL.
Dosing Regimens:
- Orally: 0.2–0.4 mg.
- Intramuscularly (IM) and intravenously (IV): 0.1–0.2 mg.
Prescription Examples:
Tablets: Rp.: Tab. Ergometrini maleatis 0.2 mg D.t.d. N. 10 S. Take 1 tablet orally twice a day.
Ampoules: Rp.: Sol. Ergometrini maleatis 0.02% - 1 mL D.t.d. N. 5 in amp. S. Administer 1 mL intramuscularly.