An adolescent is brought drowsy with flushed dry skin, dilated pupils, sinus tachycardia, urinary retention and temperature of 39 degrees Celsius after eating seeds of Datura stramonium. ECG shows narrow complex tachycardia without QRS widening. Which antidote is most appropriate?

• A Naloxone
• B Flumazenil
• C Neostigmine
• D Physostigmine ✓

Explanation

This is the classic antimuscarinic toxidrome: hyperthermia, dry skin, mydriasis, tachycardia, delirium and urinary retention. Physostigmine is a tertiary amine anticholinesterase that crosses the blood-brain barrier and reverses both central and peripheral muscarinic blockade. Neostigmine is a quaternary ammonium compound that does not enter the CNS, so it cannot treat the life-threatening central features such as agitation and hyperthermia, and it lacks any effect on brain receptors.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.