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 preparations (the native neurohypophyseal hormone) lies in the nature of their effect on the myometrium. While oxytocin at physiological concentrations stimulates normal rhythmic labor activity, ergot alkaloids cause a persistent tonic contraction of the uterus. These are not physiological contractions, but a prolonged, continuous spasm of the smooth muscle.
In addition, the drug affects endocrine regulation: it inhibits prolactin secretion, which naturally leads to the suppression of breast milk production (reduced lactation).
Clinical use and biomechanics of hemostasis
The main goal of prescribing ergometrine is to stop bleeding. It is important to clearly understand the pathogenetic rationale: the drug does not increase blood clotting and has no direct effect on coagulation factors.
Its hemostatic effect is purely biomechanical in nature. A powerful tonic contraction of the myometrium causes the muscle fibers to physically (mechanically) compress the gaping uterine blood vessels.
Main indications for use:
- Management of hypotonic hemorrhage in the early postpartum period.
- Bleeding following artificial termination of pregnancy (abortions).
- Uterine bleeding in non-pregnant patients.
- Decreased uterine tone after childbirth.
Contraindications and side effects
The drug is strictly contraindicated during pregnancy and labor until the placenta is completely delivered.
Why cannot ergometrine be used for labor induction? Due to a sharp increase in basal myometrial tone, uteroplacental blood flow is impaired. This creates a very high risk of acute fetal hypoxia. To enhance labor activity, oxytocin, pituitrin, or dinoprost are used, but under no circumstances ergot alkaloids.
It should also be remembered that in hypotonic hemorrhage, tocolytics are contraindicated (atosiban, salbutamol, magnesium sulfate). They relax the uterus and will only increase blood loss.
Side effects of the drug:
- CNS: headache, vivid hallucinations.
- GI tract: nausea, vomiting, diarrhea, abdominal pain.
Overdose or ergot poisoning leads to ergotism. In addition to hallucinations and dyspepsia, it is characterized by persistent spasm of the peripheral vessels of the extremities with endothelial damage, which in severe cases leads to gangrene.
Formulations and prescription rules
The drug is available in enteral and parenteral forms. Dosages are extremely small, so it is important not to make mistakes with zeros when writing the prescription.
- Tablets: 0.0002 g each.
- Solution in ampoules: 0.02% with a volume of 0.5 ml and 1 ml.
Dosing regimens:
- Orally (per os), the dose is 0.0002–0.0004 g.
- Intramuscularly (IM) and intravenously (IV), administer 0.0001–0.0002 g.
Sample prescriptions:
For tablets: Rp.: Tab. Ergometrini maleatis 0.0002 D.t.d. N. 10 S. Take 1 tablet orally 2 times a day.
For ampoules: Rp.: Sol. Ergometrini maleatis 0.02% - 1 ml D.t.d. N. 5 in amp. S. Administer 1 ml intramuscularly.
Ergometrine is an energetic expander: it squeezes the uterus into a steel fist (tonic contraction), pushing out blood and milk (stopping bleeding, blocking prolactin).
Class and exam questions
Can ergometrine be used to stimulate weak labor activity?
Categorically no. It causes tonic spasm rather than physiological rhythmic contractions. This will lead to impaired placental blood flow and severe fetal hypoxia.
How does ergometrine stop bleeding if it does not affect clotting factors?
Its effect is purely biomechanical. Sustained myometrial contraction acts like a physical tourniquet, with muscle fibers compressing the gaping uterine vessels.
Does the drug affect breastfeeding?
Yes, it inhibits prolactin secretion, leading to lactation suppression and reduced breast milk production.
What is ergotism and how does it manifest?
This is ergot alkaloid poisoning. It manifests as vivid hallucinations, nausea, diarrhea, and persistent vasospasm of the extremities, threatening the development of gangrene.
What else to study on this topic
- Differences in the pharmacodynamics of oxytocin and ergometrine
- Tocolytics: drugs that relax the myometrium (atosiban, salbutamol)
- Ergotamine: use of ergot alkaloids in migraine
- Synthetic agents increasing uterine tone (cotarnine chloride)
- Pathogenesis of vascular complications in ergotism
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