A young woman who ingested an unknown quantity of a belladonna alkaloid presents with agitated delirium, dry flushed skin, and dilated pupils. The physician chooses physostigmine rather than neostigmine as the antidote. The basis for this choice is that physostigmine:

• A Has a longer duration of cholinesterase inhibition
• B Directly stimulates central muscarinic receptors
• C Is a tertiary amine that penetrates the blood-brain barrier ✓
• D Does not cause bradycardia or bronchoconstriction

Explanation

Physostigmine is a tertiary amine that crosses the blood-brain barrier and can reverse the central anticholinergic syndrome of delirium and coma. Neostigmine is a quaternary ammonium compound restricted to the periphery, so it cannot reach central muscarinic receptors. Both drugs act identically as carbamate cholinesterase inhibitors peripherally, and both can produce bradycardia and bronchoconstriction, so they offer no safety advantage there.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.