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Key Features

  • Antimuscarinic agents with variable CNS effects

    • Atropine

    • Scopolamine

    • Belladonna

    • Diphenoxylate with atropine

    • Datura stramonium

    • Hyoscyamus niger

    • Some mushrooms

    • Tricyclic antidepressants

    • Antihistamines

Clinical Findings

  • Anticholinergic syndrome

    • Dryness of the mouth, thirst, difficulty swallowing, blurring of vision

    • Dilated pupils, flushed skin, tachycardia, fever, delirium, myoclonus, ileus, flushed appearance

  • Dilated pupils, flushed skin, tachycardia, fever, delirium, myoclonus, ileus, flushed appearance

  • Antidepressants and antihistamines may induce convulsions

  • Diphenhydramine commonly causes delirium, tachycardia, and seizures; massive overdose may mimic tricyclic antidepressant cardiotoxic poisoning

  • Terfenadine and astemizole cause QT interval prolongation and torsades de pointes and were removed from US market

Diagnosis

  • Based on history of ingestion, typical "anticholinergic syndrome"

  • Serum levels not useful

  • ECG monitoring for wide QRS, QT prolongation

Treatment

Emergency and supportive measures

  • Activated charcoal

    • Administer 60–100 g mixed in aqueous slurry orally or via gastric tube

    • Do not use for comatose or convulsing patients unless they are endotracheally intubated

  • External cooling and sedation, or neuromuscular paralysis in rare cases, are indicated to control high temperatures

Specific treatment

  • For severe anticholinergic syndrome, (eg, agitated delirium),

    • Give physostigmine salicylate, 0.5–1 mg intravenously slowly over 5 minutes, with ECG monitoring

    • Repeat as needed to total dose of no more than 2 mg

  • Caution: Bradyarrhythmias and convulsions are a hazard with physostigmine administration, and the drug should not be used in patients with evidence of cardiotoxic effects from tricyclic antidepressants or other sodium channel blockers

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