Anticholinergic Overdose: Signs and Symptoms
Anticholinergic overdose presents with a classic constellation of findings memorably described as "Red as a beet, dry as a bone, hot as a hare, blind as a bat, mad as a hatter, full as a flask," characterized by agitated delirium, mydriasis, hot dry flushed skin, mild fever, tachycardia, and decreased bowel sounds. 1
Central Nervous System Manifestations
- Agitated delirium is the hallmark mental status change in anticholinergic toxicity 1
- Patients may exhibit confusion, hallucinations, and pronounced delirium requiring physical restraint 2
- Severe cases can progress to seizures, coma, respiratory failure, and cardiovascular collapse 3
- Additional CNS findings include somnolence, amnesia, dysarthria, ataxia, and stupor 4
Vital Sign Abnormalities
- Mild temperature elevation (<38.8°C or <101.8°F) distinguishes anticholinergic syndrome from other hyperthermic drug toxicity syndromes 1
- Tachycardia is consistently present 1
- Tachypnea occurs as part of autonomic dysfunction 1
- Mild hypertension may be present 1
Physical Examination Findings
Skin and Mucous Membranes
- Hot, dry, erythematous (flushed) skin is pathognomonic 1
- Dry mucous membranes and dry mouth result from decreased secretions 1, 2
Ocular Findings
- Mydriasis (markedly dilated and fixed pupils) is a cardinal sign 1, 2
- Blurred vision and visual disturbances commonly occur 3, 4
Neuromuscular Examination
- Normal muscle tone differentiates anticholinergic syndrome from serotonin syndrome and neuroleptic malignant syndrome 1
- Slowed or hyporeflexic reflexes may be present 1
- Tremors and ataxia can occur 3, 4
Gastrointestinal and Genitourinary
- Hypoactive or absent bowel sounds reflect decreased GI motility 1
- Urinary retention and difficulty with micturition are common 3, 4
- Constipation results from antimuscarinic effects 3
Dose-Dependent Severity
- Mild symptoms (somnolence, anticholinergic signs, tachycardia, nausea) occur in 55-64% of cases 5
- Moderate symptoms (agitation, confusion, hallucinations, ECG disturbances) occur in 22-27% of cases, typically above 0.3g ingested dose 5
- Severe symptoms (delirium/psychosis, seizures, coma) occur in 14-18% of cases, with critical dose threshold at 1.0g 5
Common Causative Agents
Anticholinergic toxicity results from exposure to antihistamines (including diphenhydramine and cetirizine), tricyclic antidepressants, sleep aids, cold preparations, atropine, and antimuscarinic drugs 1, 5, 6. The syndrome typically develops within 0.5 to 24 hours of exposure 1.
Key Diagnostic Pitfall
Not all patients present with the complete syndrome—partial or attenuated presentations are possible, making diagnosis challenging 1. The diagnosis is often confirmed by positive therapeutic response to physostigmine, a centrally active anticholinesterase agent 3, 2, 4. Treatment considerations include sodium bicarbonate for prolonged QRS or dysrhythmias, management of hyperthermia, and physostigmine administration 1.