Pearl of the Day: Anticholinergic Toxicity

Anticholinergic Toxicity Background - sources: antihistamines, belladonna, mydriatic agents (e.g., tropicamide, cyclopentolate), TCAs, benztropine, phenothiazines, clozapine, olanzapine, Amanita muscaria - can be absorbed through ingestion, smoking, or ocular use - muscarinic blockade delays gastric emptying -> absorption and peak clinical effects are delayed - cholinergic receptors: muscarinic, nicotinic - central anticholinergic syndrome: fever, agitation, delirium, coma - peripheral anticholinergic syndrome: tachycardia, flushed dry skin, dry mouth, ileus, urinary retention - risk of toxicity is dose related

Signs/Symptoms - dry as a bone, red as a beet, hot as a hare, blind as a bat, mad as a hatter, stiff as a pipe - usually sinus tachycardia (wide-complex tachydsyrhythmias with diphenhydramine occur from sodium-channel blockade, not anticholinergic effect) - delirium described as restlessness, irritability, disorientation, auditory and visual hallucinations (e.g., Lilliputian hallucinations) - dysarthria described as staccato speech, high-pitched cries - myoclonus

Diagnosis/Work-up - BMP, CPK, urine toxicology - positive drug screen only indicates exposure, does not imply overdose - differential diagnosis: viral encephalitis, Reye's syndrome, head trauma, post-ictal state, neuroleptic malignant syndrome

Treatment - activated charcoal if ingestion within 1 hour, though may be beneficial beyond 1 hour of ingestion - multidose activated charcoal not recommended with impaired GI motility - supportive care, IVF, temperature monitoring and treatment - agitation -> benzodiazepines IV; avoid physical restraints - wide-complex tachydysrhythmias -> sodium bicarbonate IV

Physostigmine - 0.5 - 2 mg (pediatrics 0.02 mg/kg) by slow IV over 5 min - reversible acetylcholinesterase inhibitor that crosses blood-brain barrier - adverse effects of bradycardia and seizures more likely in patients without anticholinergic effects -> should not be used as diagnostic challenge - mixed evidence - may be better at controlling agitation and reversing delirium than benzodiazepines - indications: seizure, delirium, narrow QRS supraventricular tachydysrhythmias, hemodynamic deterioration - effects may occur within 15 - 20 min, requires continuous cardiac monitoring for bradycardia - may repeat dosing - asymptomatic for 6 hours -> no repeat dosing required - contraindications: asthma, intestinal/bladder obstruction, cardiac conduction disturbances, sodium-channel antagonist poisoning

Disposition - symptomatic patients (including those receiving physostigmine) require hospital obervation for at least 24 hours - patients with mild symptoms that resolve within 6 hours may be discharged

Resources Tintinalli's Emergency Medicine, 8th Edition