What Is an Example of an Anticholinergic Poison? Atropine and Other Toxins

According to U.S. Poison Centers, there are between 8,000 and 10,000 exposures to anticholinergic substances annually. A primary example of an anticholinergic poison is atropine, a naturally occurring tropane alkaloid derived from toxic plants like Atropa belladonna, or deadly nightshade.

Quick Summary

Atropine, a potent muscarinic antagonist found in plants like deadly nightshade and jimson weed, is a key example of an anticholinergic poison. Overdose leads to a characteristic toxidrome affecting the central and peripheral nervous systems, presenting with symptoms like dry mouth, dilated pupils, and confusion.

Key Points

• Classic Example: Atropine, sourced from deadly nightshade, is a potent anticholinergic poison known for its historical and medicinal significance.

• Common Sources: Besides atropine, other anticholinergic toxins are found in plants like jimson weed, and in various medications including certain antihistamines and antidepressants.

• Mechanism: These toxins block muscarinic acetylcholine receptors, which disrupts normal parasympathetic nervous system function and allows sympathetic effects to dominate.

• Key Symptoms (Toxidrome): Poisoning results in characteristic symptoms like dry, flushed skin, dilated pupils, fever, urinary retention, and altered mental status, including hallucinations.

• Treatment: Management involves supportive care to stabilize the patient, and in severe cases, the antidote physostigmine can be used to reverse central nervous system effects.

Atropine: A Classic Anticholinergic Poison

Atropine is a well-known example of an anticholinergic poison, with a history of both medicinal use and infamous toxicity. Derived from the Atropa belladonna plant, its name is a nod to its poisonous past; Atropos was the Greek Fate responsible for cutting the thread of life. In controlled medical settings, atropine is used to treat conditions like bradycardia (slow heart rate) and certain poisonings, such as from organophosphate insecticides. However, in excessive doses, it can cause severe poisoning by blocking the neurotransmitter acetylcholine at muscarinic receptors throughout the body.

Other Sources of Anticholinergic Toxins

While atropine is a prominent example, the anticholinergic syndrome can result from exposure to a wide variety of substances, both natural and synthetic.

Natural Sources (Plants)

Many plants contain anticholinergic alkaloids, leading to accidental or intentional poisoning. They are often referred to as deliriants due to their effects on the central nervous system.

• Datura stramonium (Jimson Weed): This plant, known for its spiky fruit, contains atropine, scopolamine, and hyoscyamine. All parts of the plant are highly toxic, and ingestion can cause severe hallucinations, delirium, and other anticholinergic effects.
• Atropa belladonna (Deadly Nightshade): The source of atropine, this plant is notoriously poisonous. Ingestion of its berries, especially by children, can be fatal.
• Hyoscyamus niger (Henbane): This plant also contains tropane alkaloids and can induce anticholinergic toxicity.
• Other Datura species: Several other species, including Brugmansia and Mandragora officinarum (mandrake), also contain anticholinergic compounds.

Medicinal and Recreational Sources

Overdose from certain medications or recreational drug use can also cause anticholinergic toxicity.

• Over-the-counter (OTC) medications: Many cold and sleep-aid products contain antihistamines, such as diphenhydramine (Benadryl) and doxylamine, which have potent anticholinergic properties.
• Prescription medications: Classes of drugs with anticholinergic effects include tricyclic antidepressants (e.g., amitriptyline), some antipsychotics (e.g., clozapine), and certain antispasmodics (e.g., oxybutynin).
• Adulterated street drugs: Scopolamine, another potent anticholinergic, has been found as a cutting agent in illicit drugs like heroin, leading to unpredictable poisonings.

The Mechanism Behind Anticholinergic Toxicity

Anticholinergic agents exert their toxic effects by competitively blocking the action of acetylcholine at muscarinic receptors. Acetylcholine is a key neurotransmitter in the parasympathetic nervous system, responsible for "rest and digest" functions. By blocking these receptors, anticholinergics inhibit normal parasympathetic tone, allowing the sympathetic nervous system to dominate.

This widespread receptor blockade leads to a characteristic set of symptoms, known as the anticholinergic toxidrome, which affects multiple bodily systems including the central nervous system, heart, and glands. The severity of symptoms depends on the dose and the specific substance ingested.

Common Symptoms of Anticholinergic Poisoning

The anticholinergic toxidrome is often summarized by several memorable rhymes:

• "Red as a beet" (flushed, dry skin)
• "Dry as a bone" (dry mouth, decreased sweating)
• "Blind as a bat" (dilated pupils causing blurred vision and photophobia)
• "Mad as a hatter" (agitation, confusion, hallucinations)
• "Hot as a hare" (fever or hyperthermia)
• "Full as a flask" (urinary retention)

Other symptoms may include rapid heart rate (tachycardia), difficulty swallowing, decreased bowel sounds, and a lack of coordination. In severe cases, high doses can lead to seizures, coma, respiratory failure, and even death.

Diagnosis and Treatment of Anticholinergic Poisoning

Diagnosis of anticholinergic poisoning relies primarily on a thorough history and physical examination, recognizing the characteristic clinical findings. In cases of intentional overdose or ingestion of unknown substances, laboratory tests may be necessary to rule out other toxicities.

Treatment focuses on supportive care and the potential use of a specific antidote.

Supportive Care

• ABC Management: Ensuring the patient's airway, breathing, and circulation are stable is the priority.
• Decontamination: For recent oral ingestions, activated charcoal can be administered to prevent further absorption of the poison.
• Managing Agitation and Seizures: Benzodiazepines (e.g., lorazepam or diazepam) are the preferred treatment for severe agitation or seizures.
• Cooling: If fever is present, cooling measures like alcohol sponges or misting may be used.

Specific Antidote: Physostigmine

In cases of severe anticholinergic delirium or other significant central nervous system effects, physostigmine can be administered. This drug is an acetylcholinesterase inhibitor that increases the amount of acetylcholine in the synapse, helping to overcome the muscarinic receptor blockade. Physostigmine can rapidly reverse central symptoms like delirium, agitation, and hallucinations. However, its use is carefully considered due to potential side effects and is contraindicated in certain cardiac conditions or tricyclic antidepressant overdose.

Comparison: Anticholinergic vs. Sympathomimetic Toxicity

Differential diagnosis can be challenging, as some symptoms overlap with other conditions. A key distinction is often made with sympathomimetic toxicity, caused by substances like cocaine or methamphetamine.

Feature	Anticholinergic Poisoning (e.g., Atropine)	Sympathomimetic Poisoning (e.g., Cocaine)
Heart Rate	Tachycardia	Tachycardia
Blood Pressure	Increased	Increased
Pupils	Mydriasis (dilated)	Mydriasis (dilated)
Skin	Dry and flushed	Diaphoretic (sweaty)
Bowel Sounds	Decreased or absent	Increased
Mental Status	Agitation, delirium, hallucinations	Anxiety, agitation, paranoia

Conclusion

Answering the question "What is an example of an anticholinergic poison?" points directly to atropine, a potent compound with a history stretching back centuries. However, the scope of anticholinergic toxins extends beyond this single example to include many common plants and pharmaceutical agents. Understanding the characteristic toxidrome and the mechanism of action is critical for recognizing and effectively managing cases of poisoning. While supportive care forms the backbone of treatment, specific antidotes like physostigmine can be life-saving in severe central nervous system toxicity. As with any poisoning, rapid identification and medical intervention are paramount to ensuring a positive outcome.

Note: This article is for informational purposes only and does not constitute medical advice. If anticholinergic poisoning is suspected, contact a poison control center immediately.

Additional Resources

For more in-depth information, consult authoritative sources such as the Anticholinergic Toxicity entry from StatPearls on the NCBI Bookshelf.

Frequently Asked Questions

What is the most common plant-based anticholinergic poison?

The most common plant source of anticholinergic poisoning is Datura stramonium, also known as jimson weed or thorn apple. It contains potent tropane alkaloids, including atropine and scopolamine.

What are the first signs of anticholinergic poisoning?

Initial signs often include dry mouth, blurred vision from dilated pupils, and a flushed, hot, and dry skin appearance. These are often followed by an increased heart rate and altered mental state.

How is anticholinergic poisoning treated?

Treatment begins with supportive care, such as managing the airway and fluid balance. For severe central nervous system symptoms like delirium and hallucinations, the specific antidote physostigmine may be administered to reverse the effects.

Can over-the-counter medications cause anticholinergic poisoning?

Yes. Many OTC sleep aids and cold preparations contain antihistamines, such as diphenhydramine, which have strong anticholinergic properties and can cause toxicity, especially in overdose.

What does 'anticholinergic' mean?

Anticholinergic refers to a substance that blocks the action of the neurotransmitter acetylcholine, specifically at muscarinic receptor sites in the body. This disruption affects a wide range of functions regulated by the parasympathetic nervous system.

Why does anticholinergic poisoning cause hallucinations?

The anticholinergic compounds, like atropine and scopolamine, can cross the blood-brain barrier. When they block muscarinic receptors in the central nervous system, it leads to disorganization of brain activity, resulting in confusion, delirium, and hallucinations.

Is anticholinergic poisoning always fatal?

Fatalities are rare, especially in adults, though they can occur with large ingestions. Most exposures are not fatal due to rapid treatment and the rapid excretion of the drug. However, the effects can be severe and require immediate medical attention.