Ergometrine, Methylergometrine - Uterine Stimulants

| Home | | Pharmacology |

Chapter: Essential pharmacology : Oxytocin And Other Drugs Acting On Uterus

The amine ergot alkaloid ergometrine (ergonovine) and its derivative methylergometrine are used in obstetrics. Both have similar pharmacological property.


ERGOMETRINE, METHYLERGOMETRINE

 

The pharmacology of ergot alkaloids is described in Ch. No. 12. Only the amine ergot alkaloid ergometrine (ergonovine) and its derivative methylergometrine are used in obstetrics. Both have similar pharmacological property.

 

Uterus

 

They increase force, frequency and duration of uterine contractions. At low doses, contractions are phasic with normal relaxation in between, but only moderate increase in dose raises the basal tone, contracture occurs with high doses. Gravid uterus is more sensitive, especially at term and in early puerperium. Their stimulant action involves the lower segment also. The uterotonic action is believed to result from partial agonistic action on 5HT2 and α adrenergic receptors.

 

CVS

 

Ergometrine and methylergometrine are much weaker vasoconstrictors than ergotamine and have low propensity to cause endothelial damage. Though they can raise BP, this is not significant at doses used in obstetrics.

 

CNS

 

No overt effects occur at usual doses. However, high doses produce complex actions— partial agonistic/antagonistic interaction with adrenergic, serotonergic and dopaminergic receptors in the brain have been shown.

 

GIT

 

High doses can increase peristalsis. Methylergometrine is 1½ times more potent than ergometrine on the uterus, but other actions are less marked. It has thus replaced ergometrine at many obstetric units.

 

Pharmacokinetics

 

In contrast to the amino acid ergot alkaloids, ergometrine and methylergometrine are rapidly and nearly completely absorbed from the oral route. The onset of uterine action is: Oral—15 min; i.m.—5 min; i.v.—almost immediate.

 

They are partly metabolized in liver and excreted in urine. Plasma t½ is 1–2 hours. Effects of a single dose last 3–4 hours.

 

Adverse Effects

 

Ergometrine and methylergometrine are less toxic than ergotamine. When correctly used in obstetrics—hardly any complications arise, especially with methylergometrine. Nausea, vomiting and rise in BP occur occasionally. It can decrease milk secretion if higher doses are used for many days postpartum; this is due to inhibition of prolactin release (dopaminergic action).

 

Ergometrine should be avoided in—

 

1. patients with vascular disease, hypertension, toxaemia.

2. presence of sepsis—may cause gangrene.

3. liver and kidney disease.

 

They are contraindicated during pregnancy and before 3rd stage of labour.

 

Use

 

1) The primary indication for ergometrine/ methylergometrine is to control and prevent postpartum haemorrhage (PPH): 0.2–0.3 mg i.m. at delivery of anterior shoulder reduces postpartal blood loss and prevents PPH. However, routine use in all cases is not justified—only in those expected to bleed more, e.g. grand multipara, uterine inertia. Multiple pregnancy should be excluded before injecting.

 

If PPH is occurring—0.5 mg i.v. is recommended.

 

These drugs produce sustained tonic uterine contraction: perforating uterine arteries are compressed by the myometrial meshwork— bleeding stops.

 

2) After cesarean section/instrumental delivery —to prevent uterine atony.

 

3) To ensure normal involution: A firm and active uterus involutes rapidly. To ensure this: 0.125 mg of ergometrine or methylergometrine has been given TDS orally for 7 days. However, routine use in all cases is not justified because normal involution is not hastened. Multipara and others in whom slow involution is feared—may be given prophylactically.

 

4) Diagnosis of variant angina: A small dose of ergometrine injected i.v. during coronary angiography causes prompt constriction of reactive segments of coronary artery that are responsible for variant angina.

 

ERGOMETRINE 0.25, 0.5 mg tab, 0.5 mg/ml inj. Methylergometrine: METHERGIN, METHERONE, ERGOMET 0.125 mg tab, 0.2 mg/ml inj.


Contact Us, Privacy Policy, Terms and Compliant, DMCA Policy and Compliant

TH 2019 - 2022 pharmacy180.com; Developed by Therithal info.