Makindo Medical Notes

Related Subjects: Acute Kidney Injury |Acute Rhabdomyolysis |Hyperkalaemia |Neuroleptic Malignant Syndrome |Malignant Hyperpyrexia (Malignant Hyperthermia) |Serotonin syndrome |Cholinergic crisis-syndrome |Anticholinergic syndrome

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.