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

  • Physostigmine is a reversible cholinesterase inhibitor that can cross the blood-brain barrier so in theory it would be a useful antidote BUT…

  • There is a black box warning for asystole and seizures when physostigmine is used this way

  • Therefore it is contraindicated in TCA overdoses

  • However, it is still indicated 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

References

1. Arens AM, Shah K, Al-Abri S, Olson KR, Kearney T. Safety and effectiveness of physostigmine: a 10-year retrospective review^{. 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