A 68-year-old man with COPD presents to the emergency department with acute onset of severe mydriasis, cycloplegia, tachycardia (HR 118/min), dry mouth, and confusion. He was found at home with an empty bottle of his wife's antihistamine medication (diphenhydramine). Vital signs: BP 148/92 mmHg, RR 24/min, temp 38.2°C. What is the most appropriate immediate management?

Explanation

## Anticholinergic Toxidrome Management ### Clinical Presentation Identification **Key Point:** The triad of mydriasis, tachycardia, dry mouth, plus CNS effects (confusion) and fever defines anticholinergic toxidrome — a medical emergency requiring active reversal. ### Mechanism of Diphenhydramine Toxicity Diphenhydramine is a first-generation antihistamine with potent anticholinergic properties. Overdose blocks muscarinic receptors systemically, causing: - Peripheral: mydriasis, cycloplegia, dry mouth, tachycardia, urinary retention - Central: confusion, agitation, seizures, hyperthermia ### Why Physostigmine Is the Answer **High-Yield:** Physostigmine is a tertiary amine anticholinesterase that crosses the blood–brain barrier, making it the only anticholinesterase suitable for CNS anticholinergic toxidrome (including atropine poisoning and anticholinergic drug overdose). **Clinical Pearl:** Physostigmine reverses BOTH central and peripheral anticholinergic signs by increasing acetylcholine at the synapse. Dosing: 1–2 mg IV slowly over 5 minutes, with continuous cardiac monitoring (risk of cholinergic crisis if overdosed). ### Why Not Atropine? **Warning:** Atropine is itself an anticholinergic drug — it would WORSEN the toxidrome, not reverse it. This is a critical trap. ### Why Not Observation Alone? Anticholinergic toxidrome with CNS involvement (confusion, hyperthermia) is NOT self-limited and carries risk of seizures, arrhythmias, and death if untreated. Active reversal is indicated. ### Why Not Benzodiazepines Only? Benzodiazepines manage agitation and seizure risk but do NOT reverse the underlying anticholinergic blockade. They are adjunctive, not primary therapy. **Mnemonic:** **SLUDGE** (Salivation, Lacrimation, Urination, Defecation, GI upset, Emesis) = cholinergic excess (physostigmine effect); **DRY as a BONE, MAD as a HATTER, RED as a BEET, HOT as a PISTOL** = anticholinergic toxidrome (what physostigmine reverses).