A patient who received a large overdose of a belladonna alkaloid presents with delirium, flushed dry skin, dilated pupils, and tachycardia. Which antidote is appropriate, and why?
- A Physostigmine, because its tertiary amine structure allows entry into the central nervous system ✓
- B Neostigmine, because it penetrates the central nervous system effectively
- C Pralidoxime, because it regenerates muscarinic receptors
- D Atropine, because competitive antagonism reverses the delirium
Correct answer: A. Physostigmine, because its tertiary amine structure allows entry into the central nervous system
Explanation
Anticholinergic delirium reflects central muscarinic blockade, so the antidote must cross the blood-brain barrier. Physostigmine is a tertiary amine and enters the CNS, where it raises acetylcholine levels and reverses both central and peripheral anticholinergic toxicity. Neostigmine is a quaternary ammonium compound that does not cross the blood-brain barrier, limiting it to peripheral effects. Pralidoxime regenerates phosphorylated cholinesterase in organophosphate poisoning and has no role here.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
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