Related Subjects:
Acute Kidney Injury
|Acute Rhabdomyolysis
|Hyperkalaemia
|Neuroleptic Malignant Syndrome
|Malignant Hyperpyrexia (Malignant Hyperthermia)
|Serotonin syndrome
|Cholinergic crisis-syndrome
|Anticholinergic syndrome
ℹ️ About
- Anticholinergic syndrome occurs when acetylcholine action at muscarinic receptors is blocked in both the central and peripheral nervous system. 🧠🫀
- This disrupts normal parasympathetic function → unopposed sympathetic tone.
- Causes a characteristic toxidrome often summarised in the classic phrase:
“Red as a beet (flushing), Dry as a bone (anhidrosis/xerostomia), Blind as a bat (mydriasis), Mad as a hatter (delirium), Hot as a hare (fever), Full as a flask (urinary retention).”
Causes
- Medications:
- Antihistamines (e.g. diphenhydramine, chlorpheniramine)
- Tricyclic antidepressants (e.g. amitriptyline, imipramine)
- Antipsychotics (e.g. chlorpromazine, clozapine)
- Antiparkinsonian drugs (e.g. benztropine, trihexyphenidyl)
- Atropine, scopolamine (direct muscarinic blockers)
- Plants: Belladonna (deadly nightshade), Jimsonweed (Datura stramonium), Henbane - rich in atropine, scopolamine, hyoscyamine alkaloids. 🌿
Clinical Features 🩺
- Peripheral (parasympathetic blockade):
- Dry flushed skin, dry mouth (anhidrosis, xerostomia)
- Mydriasis with photophobia, blurred vision (loss of accommodation)
- Tachycardia, hypertension
- Decreased bowel sounds → ileus
- Urinary retention
- Central (CNS muscarinic blockade):
- Agitation, delirium, hallucinations (visual & auditory)
- Confusion, short-term memory loss
- Ataxia, myoclonic jerks
- Severe: seizures, coma, respiratory depression, cardiovascular collapse
Investigations 🔬
- Primarily clinical diagnosis (classic toxidrome).
- ECG: Important to check for widened QRS / prolonged QT (esp. with TCA overdose).
- U&E, renal function (dehydration, rhabdomyolysis risk if agitated).
- CK if prolonged agitation/seizures (risk of rhabdomyolysis).
Management 💉
- Supportive care (cornerstone):
- Airway protection & oxygenation
- IV fluids for hydration & circulation
- Cooling for hyperthermia
- Continuous ECG monitoring for arrhythmias
- Catheterisation for urinary retention
- Symptomatic treatment:
- Benzodiazepines (diazepam, lorazepam) for agitation, delirium, or seizures
- Antiemetics for nausea/vomiting
- Activated charcoal if ingestion <1h and airway protected
- Specific antidote (use with caution):
- Physostigmine (reversible AChE inhibitor) may reverse central & peripheral symptoms.
- Indicated in severe agitation/delirium unresponsive to benzodiazepines.
- Dose: 0.5–2 mg IV slowly, repeat every 10–15 min as needed.
- Contraindications: Suspected TCA overdose (risk of asystole, seizures).
Clinical Pearls ✨
- 🧠 Differentiate from sympathomimetic toxicity: Both cause agitation, tachycardia, mydriasis - but anticholinergic has dry skin & absent sweating (vs sweaty in sympathomimetics).
- 🌿 Plant ingestion (e.g. Jimsonweed tea) → classic OSCE scenario.
- 💊 Physostigmine can dramatically improve delirium but is risky - only use if diagnosis certain & ECG excludes TCA toxicity.
- ⚠️ Always look for hidden polypharmacy: elderly patients on multiple anticholinergic burden drugs are at high risk.
