Classification and General Characteristics
In pharmacology, agents that increase myometrial tone through sustained tonic contraction are divided into ergot alkaloids and synthetic drugs. Ergot alkaloids include ergometrine and ergotamine.
The raw material source is the sclerotium stage of the fungus Claviceps purpurea, which parasitizes rye (Secale cornutum). The main mechanism of hemostasis during their use is the mechanical compression of blood vessel walls by the contracted muscle fibers of the uterus.
Pharmacodynamics and medical use
These medicinal substances have a narrow but critically important application in medical practice. The main indications include:
- Stopping uterine bleeding occurring outside of pregnancy.
- Early postpartum hemorrhage.
- Bleeding after artificial termination of pregnancy (abortion).
- Accelerating uterine involution (retrogressive changes) after childbirth.
- Reducing uterine tone in the postpartum period.
An absolute contraindication to prescribing these agents is the acceleration of labor. Spasm of the myometrium during labor will inevitably lead to fetal asphyxia.
Ergometrine and ergotamine: drug characteristics
Ergometrine is a natural alkaloid that acts as a $5-HT_{2A}$ receptor agonist (serotonin). An interesting feature of the drug is its effect on lactation: it suppresses prolactin secretion, thereby inhibiting milk production. Side effects include headache, hallucinations, nausea, diarrhea, and abdominal pain.
Ergotamine is used in obstetrics similarly to ergometrine, but has a unique vascular effect. It reduces the pulse amplitude of cerebral blood vessels, which is why it is used to treat migraine and vascular headaches.
Toxicology: ergotism and synthetic analogue
Prolonged or excessive use of ergot causes severe poisoning—ergotism. Its symptoms include vivid hallucinations, nausea, vomiting, and diarrhea. Vascular disorders in ergotism manifest as persistent vasospasm of the extremities combined with endothelial damage, which carries a high risk of gangrene.
The group of agents affecting uterine tone and hemostasis also includes cotarnine chloride (stypticin), a synthetic dihydroisoquinoline derivative. It can be administered orally, parenterally, or used topically as a 1–2% aqueous solution to stop minor bleeding.
Briefly: answers to topical questions
What types of receptors do ergot alkaloids interact with?
Ergot alkaloids and their derivatives interact with serotonin and adrenergic receptors.
- Serotonin receptors — ergometrine is a $5-HT_{2A}$ receptor agonist, while ergotamine and dihydroergotamine stimulate 5-HT receptors, particularly the $5-HT_{1D}$ subtype.
- $\alpha$-Adrenergic receptors — natural alkaloids and dihydrogenated derivatives possess $\alpha$-adrenolytic activity; dihydroergotamine is noted for blocking $\alpha_1$- and $\alpha_2$-adrenergic receptors.
What are the clinical manifestations of ergot poisoning (ergotism)?
Clinical manifestations of ergotism include severe damage to the central nervous system, gastrointestinal tract, and blood vessels.
- Acute form — symptoms of gastroenteritis, paresthesia, convulsions, vivid hallucinations, nausea, vomiting, and diarrhea.
- Chronic form — sensation of "crawling ants" in the extremities, vomiting, GI disorders, and possible infertility.
There are three clinical forms of the disease:
- Convulsive — toxic tonic contractions of flexor muscles lasting about a month.
- Gangrenous — persistent vasospasm and endothelial damage cause necrosis of the peripheral parts of the limbs accompanied by severe pain.
- Mixed.
What are the contraindications to the use of ergot alkaloids, other than stimulating labor?
For ergometrine, pregnancy and the period of labor prior to the delivery of the placenta are contraindicated.
Which drugs belong to the group of dihydrogenated ergot alkaloids?
The group of dihydrogenated ergot alkaloids includes non-selective $\alpha$-blockers that are derivatives of D-lysergic acid. This group includes the following drugs:
- Dihydroergotamine — used as a nasal spray to abort migraine attacks.
- Dihydroergotoxine — a representative of the non-selective $\alpha$-blocker group.
- Dihydroergocryptine — used as part of the combined drug Vasobral for the treatment of vascular diseases.
Ergometrine is for the uterus (metra), ergotamine is for migraines in the head (tamine/head).
Class and exam questions
Why are ergot alkaloids contraindicated during labor?
They cause sustained tonic contraction of the myometrium rather than rhythmic labor activity. Such a spasm cuts off blood flow and leads to fetal asphyxia.
What is the mechanism of stopping bleeding during their use?
Hemostasis is achieved through mechanical compression of blood vessels by the walls of the contracted muscle fibers of the uterus.
How does ergometrine affect breastfeeding?
Ergometrine suppresses prolactin secretion, which leads to the inhibition of breast milk production.
What is the specific medical use of ergotamine outside of obstetrics?
Ergotamine reduces the pulse amplitude of cerebral blood vessels, which is why it is used to abort migraine attacks and vascular headaches.
What else to study on this topic
- Mechanism of action of ergometrine via serotonin $5-HT_{2A}$ receptors
- Pathogenesis of ergotism and vascular endothelial damage
- Pharmacological properties of synthetic cotarnine chloride
- Comparison of the effects of oxytocin and ergot alkaloids on the myometrium
- CNS and GI side effects of ergometrine administration
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