A 20-year-old student is brought to the emergency department with dilated pupils, dry flushed skin, urinary retention, and vivid visual hallucinations after ingesting seeds of Datura stramonium. Which drug is most appropriate to reverse his delirium?

• A Neostigmine
• B Pyridostigmine
• C Edrophonium
• D Physostigmine ✓

Explanation

Physostigmine is a tertiary amine that crosses the blood-brain barrier, so it can reverse both the peripheral and central features of anticholinergic toxicity such as delirium and hallucination. Neostigmine, pyridostigmine and edrophonium are all quaternary ammonium compounds that do not enter the CNS, so they would improve the peripheral signs but leave the life-threatening central anticholinergic syndrome untouched. This BBB penetration is exactly what distinguishes physostigmine from its quaternary congeners.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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