Atropine: Functions and Adverse Effects

· April 28, 2019
Atropine is a drug that acts as an antagonist to the muscarinic acetylcholine receptors and has many pharmacological effects. Read all about it in this article!

Atropine is a medication. Doctors use it for many different things. It has mydriatic, antispasmodic, antidiarrheal, antidiarrhea, anti-catarrhal, and anesthetic properties.

This active substance comes from the belladonna plant and other plants in the Solanaceae family. Since ancient times, the Hindus have been using belladonna preparations. Later on, in the Roman Empire and the Middle Ages, they used them for toxic purposes.

Throughout this article, we’ll explain the following about atropine in more detail:

  • How it works
  • Its pharmacokinetics
  • Its pharmacological effects
  • Adverse reactions

However, before we start, you must know what acetylcholine receptors are in order to better understand how it works.

Acetylcholine Receptors

The belladonna plant.

Atropine is an active ingredient that stems from Solanaceae plants such as belladonna. It has been used since ancient times.

Acetylcholine receptors are a group of receptors that also encompasses two other types of receptors. These are muscarinic and nicotinic. Basically, they’re located in the synaptic cleft. They’re mostly at a postganglionic level. However, there are some in the presynaptic level.

All neurotransmitter systems have receptors at the presynaptic level. This is because they modulate the amount of acetylcholine to be released.

Acetylcholine is a substance that is synthesized in the cytoplasm of motor neurons and activates acetylcholine receptors directly. However, very few presynaptic receptors trigger the secretion of this substance.

Atropine: How it Works

Basically, atropine is an antagonist of the muscarinic acetylcholine receptors. As we’ve seen, acetylcholine is a substance that activates these receptors directly.

This means that it inhibits the parasympathetic nervous system. Essentially, the explanation for this lies in the fact that acetylcholine receptors are in parasympathetic effectors. Thus, when someone takes atropine, it affects the heart, the eyes, and the digestive tract, among other organs.

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Pharmacokinetics

A fetus in the womb.

Overall, this medicine can be taken orally, intravenously, and many other ways, as well. If it’s administered orally, it’s easily absorbed in the digestive tract. Then, it travels through the bloodstream.

It’s a highly soluble drug. This means that it’s capable of crossing the blood-brain barrier and the placenta. Thus, pregnant women should be especially careful if they’re being treated with atropine.

It has a half-life of approximately two to three hours. Furthermore, it’s metabolized between 50% and 75% by the liver. Then, the body excretes both the metabolites and the fraction of unmetabolized drug in urine.

Pharmacological Effects

Atropine blocks the activity of the muscarinic acetylcholine receptors. Basically, this means it doesn’t allow acetylcholine to interact with those receptors.

It does this gradually in a series of structures such as the salivary, submucosal, and sweat glands, vascular smooth muscle, cardiac system, digestive and urinary tract, gastric glands, and autonomic ganglions.

Since it’s an anti-cholinergic agent in all these body parts, some of the things that it triggers are:

  • Tachycardia. This is why it’s used to increase heart rate during emergencies.
  • At the digestive level, it minimizes peristalsis and gastrointestinal spasms, cramps, and secretions.
  • It makes urination difficult. This is problematic in patients with benign prostatic hyperplasia.
  • Mydriasis. It blocks the ciliary muscle, causing spasms. However, the drug doesn’t inhibit the muscarinic receptors of the eyes if it’s administered orally.

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Adverse Reactions to Atropine

The adverse effects of this drug are related to the dose. They’re common reactions, especially in children. Furthermore, atropine can build up and produce systemic effects after multiple doses by inhalation in the elderly.

In adults, the most common side effects are:

  • Dry mouth
  • Red and hot skin due to lack of sweating
  • Fever
  • Constipation