Oxytocic Drugs in Pregnancy and Labour: An Explainer for Africans

 

By: Dr. Azuka Ezeike, MBBS, FWACS (Obstetrics and Gynaecology), MSc (Public Health), Freelance Medical Writer.

Medical review by: Ruth Abi, B. Pharm.

Classes of oxytocic drugs

 

Highlights 

• Oxytocic drugs help start or strengthen uterine contractions, aiding in labour and controlling bleeding.

• Three main types: oxytocin and analogues, ergot alkaloids, and prostaglandin analogues.

• Used for medical termination of pregnancy, miscarriage management, labour induction, and postpartum haemorrhage prevention and treatment.

• Administration routes include oral, sublingual, rectal, vaginal, intracervical, intravenous, intramuscular, and intramyometrial.

• Side effects can be on both the mother and baby.

• Accessibility varies in Africa, with some drugs more readily available than others.

 

What Are Oxytocic Drugs?

Oxytocic drugs are used to either initiate or strengthen the contraction of the muscles of the uterus (womb). They derive their name from oxytocin, the natural hormone produced by the brain that causes the contraction of the muscles in the breast and the womb. They are also called uterotonics or ecbolics because of their role in stimulating and improving the tone of the uterus. [1, 2] They are beneficial drugs in the management of pregnancy, labour and complications of pregnancy and most are included in the WHO list of essential medicines for reproductive health. [3]  Oxytocics play a crucial role in reducing maternal deaths in Africa. 

There are three basic groups of oxytocics:

• Oxytocin and oxytocin-like drugs, e.g., Oxytocin, Carbetocin
• Ergot alkaloids, e.g., ergometrine

• Prostaglandin analogues, e.g., misoprostol, dinoprostone, carboprost

 

How Do Oxytocic Drugs Work?

The exact mechanism of action depends on the specific group of oxytocic drugs. 

1. Oxytocin and Oxytocin-like Drugs

This class consists of two types

• Oxytocin- It is a naturally occurring hormone. The synthetic derivative is marketed under many brand names.
• Carbetocin - It is synthetically derived from oxytocin by adjusting some of the molecules. It has a heat-stable formulation that enables it to be stored at room temperature.

The drugs work by attaching to the oxytocin sense organ (receptors) in the womb. This leads to a series of events that eventually result in the release of a mineral called calcium within the muscle cells of the womb. The ultimate effect is the rhythmic contraction of the womb muscles. Oxytocic drugs also cause the production of another hormone-like chemical in the body called prostaglandins. This chemical further increases contraction of the womb muscles and aid ripening of the cervix.
 

2. Ergot alkaloids 

The ergot alkaloids consist of two types:

• Ergometrine- Naturally derived from the fungus Claviceps purpurea
• Methylergometrine (Methergine)-They are semisynthetic products derived from lysergic acid

The mechanism of action of ergot alkaloids is not well known. However, it is speculated to attach to serotonin, dopamine and alpha-adrenergic sense organs (receptors) on the smooth muscles of the uterus (womb) to cause sustained contractions.

 

3. Prostaglandin Analogues       

The prostaglandin analogues are of three types

• Prostaglandin E₁ (misoprostol)
• Prostaglandin E₂ (dinoprostone) 
• Prostaglandin F_2α (carboprost tromethamine) 

They behave like the naturally occurring ‘local hormones’ called prostaglandins. They work by increasing the permeability of the coverings of the cells of the smooth muscles of the womb thereby increasing the calcium level in the cells. This leads to contractions of the muscles of the womb. In addition, misoprostol and dinoprostone also cause the softening of the cervix thus facilitating dilatation in labour. 

 

What Are the Uses of Oxytocic Drugs?

Oxytocic drugs are utilised during pregnancy, labour and post-delivery. [4] While some can be used during pregnancy some are only indicated for use after delivery. 

 

Pregnancy

• Medical termination of pregnancy (where indicated) - misoprostol, dinoprostone, carboprost.

• Completion of a miscarriage - misoprostol, dinoprostone, carboprost.

• Induction of labour - misoprostol, oxytocin. [5]

 

Labour

• Augmentation of labour - oxytocin

 

Post-delivery

• Prevention of postpartum haemorrhage - oxytocin, carbetocin, misoprostol.

• Treatment of postpartum haemorrhage - oxytocin, ergometrine, misoprostol, carboprost

 

In addition to its therapeutic use, oxytocin can also be used for diagnosis. It is used to stimulate contractions in the Contraction Stress Test. This is one of the methods of assessing the well-being of the baby before delivery.

 

What Are the Available Oxytocic Drugs in Africa?

Many oxytocics are available in Africa, while some are relatively cheap and accessible, some others are not so available because of the cost.

The very readily available oxytocics include:

• Misoprostol

• Oxytocin

• Ergometrine

 

The not-so-readily-available oxytocics include:

• Combination of Ergometrine and Oxytocin

• Carbetocin

• Heat Stable carbetocin

• Dinoprostone

 

How Are Oxytocic Drugs Administered?

Oxytocics are administered on doctor's prescription only. The routes of administration include; (See table 1)

• Oral (swallowed) - misoprostol, ergometrine, carboprost

• Sublingual (under the tongue) - misoprostol

• Rectal (into the anus) - misoprostol

• Vaginal (into the vagina) - misoprostol

• Intracervical (inside the cervix) - dinoprostone

• Intravenous (through the veins) - oxytocin, carbetocin, ergometrine

• Intramuscular (into the muscles) - oxytocin, carbetocin, ergometrine, carboprost

• Intramyometrial (into the womb muscles) - carboprost

• Intra-amniotic/Extra amniotic (into or outside the amniotic sac) - Carboprost

TABLE 1: Comparison of the characteristics of the different oxytocic drugs. Click on image to enlarge.

 

What Are the Adverse Effects of Oxytocic Drugs?

While oxytocic drugs are safe when used according to directions, occasionally they can have side effects on both the mother and the baby. The side effects also depend on the drug used. (See table 1)

Side effects on the mother

• Nausea and vomiting

• Uterine hyperstimulation (overactivity, i.e., too much contraction) of the muscles of the womb

• Water intoxication due to the retention of water in the body

• Uterine rupture due to overactivity

• Hypotension (reduced blood pressure). This is related to oxytocin use

• Hypertension/heart problems - A side effect of ergot alkaloids.

Side effects on the baby

• Abnormal heart rate (foetal distress)

• Birth asphyxia (inability of baby to cry at birth)

• Stillbirth (death inside the womb)

 

Takeaway

Oxytocic drugs are essential for managing pregnancy, labour, and post-delivery to ensure the safety of both mother and baby. While generally safe when used as prescribed, these drugs can have side effects, so it's crucial to use them under medical supervision. Understanding their uses and potential side effects helps in making informed decisions during pregnancy.

 

References:

1. Drugbank online. Uterotonic agents. [Internet, n.d.]. Cited 2024 Jul 9. Available from here.

2. El-Mowafi D.  Ecbolics (Uterine stimulants) - Obstetrics Simplified. Geneva Foundation for Medical Education and Research. [Internet, 2024 Jan. 18]. Cited 2024 Jul 9. Available from here.

3. World Health Organization. Essential medicines for reproductive health [Internet. 2006 Jan 1]. Cited 2024 Jul 9. Available from here.

4. WHO recommendations: Uterotonics for the prevention of postpartum haemorrhage [Internet. 2018 Dec. 20]. Cited 2024 Jul 9. Available from here.

5. Vrees RA. Induction of labour. Medscape. [Internet. Updated 2023 Dec 8]. Cited 2024 Jul 9; Available from here.

 

Related:

CARBETOCIN: An Essential Drug for Preventing Postpartum Haemorrhage

 

 

Published: July 13, 2024

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