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 blood-brain barrier, so useful for TCA overdoses
Indicated only in certain anticholinergic overdose 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

Episode 911: Anticholinergic Toxicity

Emergency Medical Minute