Episode 911: Anticholinergic Toxicity - The Emergency Medical Minute

Episode 911: Anticholinergic Toxicity

Contributor: Taylor Lynch MD

Educational Pearls:

  • Anticholinergics are found in many medications, including over-the-counter remedies

  • Medications include:

    • Diphenhydramine

    • Tricyclic antidepressants like amitriptyline

    • Atropine

    • Antipsychotics like olanzapine

    • Antispasmodics – dicyclomine

    • Jimsonweed

    • Muscaria mushrooms

  • Mechanism of action involves competitive antagonism of the muscarinic receptor

  • Symptomatic presentation is easily remembered via the mnemonic:

    • Dry as a bone – anhidrosis due to cholinergic antagonism at sweat glands

    • Red as a beet – cutaneous vasodilation leads to skin flushing

    • Hot as a hare – anhidrotic hyperthermia

    • Blind as a bat – pupillary dilation and ineffective accommodation

    • Mad as a hatter – anxiety, agitation, dysarthria, hallucinations, and others

  • Clinical management

    • ABCs

    • Benzodiazepines for supportive care, agitation, and seizures

    • Sodium bicarbonate for TCA toxicity due to widened QRS

    • Activated charcoal if patient present < 1 hour after ingestion

    • Temperature monitoring

    • Contact poison control with questions

  • Physostigmine controversy

    • Acetylcholinesterase inhibitor

    • Black box warning for asystole and seizure

    • Contraindicated in TCA overdoses

    • Crosses the blood-brain barrier, so in theory, it would be useful for TCA overdoses

    • However, indicated only in certain anticholinergic overdoses with delirium

  • Disposition

    • Admission criteria include: symptoms >6 hours, CNS findings, QRS prolongation, hyperthermia, and rhabdomyolysis

    • ICU admission criteria include: delirium, dysrhythmias, seizures, coma, or requirement for physostigmine drip


1. Arens AM, Shah K, Al-Abri S, Olson KR, Kearney T. Safety and effectiveness of physostigmine: a 10-year retrospective review<sup/>. Clin Toxicol (Phila). 2018;56(2):101-107. doi:10.1080/15563650.2017.1342828

2. Nguyen TT, Armengol C, Wilhoite G, Cumpston KL, Wills BK. Adverse events from physostigmine: An observational study. Am J Emerg Med. 2018;36(1):141-142. doi:10.1016/j.ajem.2017.07.006

3. Scharman E, Erdman A, Wax P, et al. Diphenhydramine and dimenhydrinate poisoning: An evidence-based consensus guideline for out-of-hospital management. Clin Toxicol. 2006;44(3):205-223. doi:10.1080/15563650600585920

4. Shervette RE 3rd, Schydlower M, Lampe RM, Fearnow RG. Jimson “loco” weed abuse in adolescents. Pediatrics. 1979;63(4):520-523.

5. Woolf AD, Erdman AR, Nelson LS, et al. Tricyclic antidepressant poisoning: An evidence-based consensus guideline for out-of-hospital management. Clin Toxicol. 2007;45(3):203-233. doi:10.1080/15563650701226192

Summarized by Jorge Chalit, OMSIII | Edited by Jorge Chalit



Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.


Stay up to date by
joining our mailing list!