A medical student presents with confusion, flushed dry skin, tachycardia and mydriasis after ingesting seeds of Datura stramonium. Which drug should be used as the specific antidote, and why?
- A Physostigmine, because its tertiary amine structure crosses the blood-brain barrier and reverses central anticholinergic toxicity ✓
- B Neostigmine, because it reverses muscarinic blockade peripherally
- C Pilocarpine, because it directly stimulates all muscarinic receptors including those in the brain
- D Atropine, because competitive antagonism requires a full agonist at higher concentration
Correct answer: A. Physostigmine, because its tertiary amine structure crosses the blood-brain barrier and reverses central anticholinergic toxicity
Explanation
Physostigmine is a tertiary amine and therefore penetrates the blood-brain barrier, allowing it to raise central acetylcholine levels and reverse both central and peripheral anticholinergic toxicity. Neostigmine and pyridostigmine are quaternary ammonium compounds that do not cross into the CNS, so they correct only peripheral signs. Pilocarpine does not meaningfully cross the blood-brain barrier either, and giving more atropine would obviously worsen the picture.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.