Question:
A 25-year-old man presents to the emergency department with dry mouth, dilated pupils, flushed skin, urinary retention, tachycardia, and altered sensorium after consuming seeds from a wild plant while trekking. His friends report that the plant was identified as Atropa belladonna. Which of the following is the specific antidote for this poisoning?
A 25-year-old man presents to the emergency department with dry mouth, dilated pupils, flushed skin, urinary retention, tachycardia, and altered sensorium after consuming seeds from a wild plant while trekking. His friends report that the plant was identified as Atropa belladonna. Which of the following is the specific antidote for this poisoning?
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Physostigmine is highly effective but must be used with caution, as it can precipitate cholinergic crisis, severe bradycardia, or seizures. It is generally contraindicated in patients with tricyclic antidepressant (TCA) overdose (which also causes anticholinergic signs) because it worsens TCA-induced cardiac conduction delays, potentially causing asystole.
Updated On: Sep 3, 2026
- Start naloxone 0.4 mg and nitrate
- IV naloxone 10 mg
- Atropine
- Physostigmine
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The Correct Option is D
Solution and Explanation
Concept:
The clinical presentation perfectly describes an acute anticholinergic toxidrome.
The classic mnemonic for anticholinergic poisoning is: "Hot as a hare (fever/flushed), blind as a bat (dilated pupils), dry as a bone (dry mouth/skin), red as a beet (vasodilation), and mad as a hatter (delirium)."
The plant ingested, *Atropa belladonna* (deadly nightshade), naturally contains toxic amounts of tropane alkaloids, predominantly atropine and scopolamine, which are potent competitive muscarinic acetylcholine receptor antagonists.
Explanation:
• Because the toxicity is driven by the blockade of acetylcholine at muscarinic receptors, the definitive pharmacological treatment aims to overcome this blockade by increasing the concentration of acetylcholine in the synaptic cleft.
• Physostigmine is a reversible acetylcholinesterase inhibitor. By inhibiting the enzyme that breaks down acetylcholine, it drastically increases acetylcholine levels, allowing it to outcompete the atropine at the receptor sites.
• Crucially, unlike neostigmine or pyridostigmine, physostigmine is a tertiary amine. This chemical structure allows it to easily cross the blood-brain barrier.
• Therefore, physostigmine reverses both the peripheral symptoms (tachycardia, urinary retention, dry mouth) AND the central nervous system symptoms (delirium, agitation, altered sensorium).
• Option (C), Atropine, is the exact poison causing the syndrome; giving it would worsen the condition.
• Options (A) and (B), Naloxone, are specific antidotes for opioid overdose, not anticholinergic poisoning.
Final answer:
Physostigmine is the specific, definitive antidote for severe central and peripheral anticholinergic toxicity caused by Atropa belladonna.
The clinical presentation perfectly describes an acute anticholinergic toxidrome.
The classic mnemonic for anticholinergic poisoning is: "Hot as a hare (fever/flushed), blind as a bat (dilated pupils), dry as a bone (dry mouth/skin), red as a beet (vasodilation), and mad as a hatter (delirium)."
The plant ingested, *Atropa belladonna* (deadly nightshade), naturally contains toxic amounts of tropane alkaloids, predominantly atropine and scopolamine, which are potent competitive muscarinic acetylcholine receptor antagonists.
Explanation:
• Because the toxicity is driven by the blockade of acetylcholine at muscarinic receptors, the definitive pharmacological treatment aims to overcome this blockade by increasing the concentration of acetylcholine in the synaptic cleft.
• Physostigmine is a reversible acetylcholinesterase inhibitor. By inhibiting the enzyme that breaks down acetylcholine, it drastically increases acetylcholine levels, allowing it to outcompete the atropine at the receptor sites.
• Crucially, unlike neostigmine or pyridostigmine, physostigmine is a tertiary amine. This chemical structure allows it to easily cross the blood-brain barrier.
• Therefore, physostigmine reverses both the peripheral symptoms (tachycardia, urinary retention, dry mouth) AND the central nervous system symptoms (delirium, agitation, altered sensorium).
• Option (C), Atropine, is the exact poison causing the syndrome; giving it would worsen the condition.
• Options (A) and (B), Naloxone, are specific antidotes for opioid overdose, not anticholinergic poisoning.
Final answer:
Physostigmine is the specific, definitive antidote for severe central and peripheral anticholinergic toxicity caused by Atropa belladonna.
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