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