Pharmacology, Toxicology and Addiction MedicineTier 1Disease (DEADMAN)

Toxidromes - anticholinergic

Description

"Red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare, full as a flask"
Mydriasis (fixed, unreactive), dry flushed skin, dry mucous membranes, urinary retention, absent bowel sounds, tachycardia, hyperthermia, agitated delirium with picking/mumbling behaviour
Causes: TCAs, first-generation antihistamines (diphenhydramine, doxylamine), antipsychotics, atropine/hyoscine, plants (Datura, deadly nightshade)

Epidemiology

Common in deliberate self-poisoning (TCAs, sedating antihistamines readily available OTC)
Elderly - cumulative anticholinergic burden from multiple prescribed drugs

Aetiopathogenesis

Muscarinic receptor antagonism
- Peripheral -> dry skin, tachycardia, urinary retention, ileus, mydriasis
- Central -> delirium, agitation, hallucinations

Diagnosis

Clinical - key discriminators from sympathomimetic: DRY skin + absent bowel sounds + fixed unreactive pupils (sympathomimetic = wet, active bowel sounds, reactive pupils)
ECG mandatory if TCA suspected - QRS widening, terminal R wave in aVR (predicts seizure/arrhythmia risk) - see poisoning-from-antidepressants

Management

Benzodiazepines for agitation/seizures
Physostigmine - reverses peripheral and central signs; reserve for severe pure anticholinergic delirium with a normal QRS
- Contraindicated if TCA co-ingestion or QRS widening - risk of asystole/seizure
Sodium bicarbonate if TCA and QRS >100 ms or arrhythmia
Cooling, bladder catheterisation, supportive care

Associations

TCA co-ingestion is the dangerous combination (cardiotoxicity)
Elderly - anticholinergic burden -> falls, delirium, worsened dementia

Natural history & complications

Usually resolves over 24-48h as the drug is metabolised
Mortality mainly from TCA cardiotoxicity/arrhythmia rather than the pure anticholinergic effect itself

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