Anticholinergic toxicity, or anticholinergic syndrome, is a condition resulting from excessive inhibition of acetylcholine at muscarinic receptors. This toxicity presents as an exaggeration of the central and peripheral adverse effects of anticholinergics. Classic clinical signs of anticholinergic toxicity are often summarized using the mnemonic "red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare, full as a flask." These symptoms reflect flushing, anhidrosis (dry skin), mydriasis (dilated pupils), delirium, hyperthermia, and urinary retention—hallmark signs of anticholinergic overdose.
Patients may present with tachycardia, absent bowel sounds, confusion, agitation, and hallucinations. In severe cases, anticholinergic toxicity can lead to seizures, coma, and even death if not promptly treated. The risk of toxicity is higher in patients taking multiple medications with anticholinergic properties, as the cumulative anticholinergic burden can increase over time.
Diagnosis of anticholinergic toxicity is primarily clinical, as there is no specific test for confirming the condition. Management of anticholinergic toxicity involves supportive care and, in severe cases, the use of physostigmine, a cholinesterase inhibitor that can cross the blood-brain barrier and reverse both central and peripheral effects by increasing acetylcholine levels. However, physostigmine should be used with caution, as it can have its own risks, including cholinergic toxicity. Benzodiazepines may be used to manage agitation and seizures in the setting of anticholinergic toxicity.
| Element | Detail |
|---|---|
| Classic mnemonic | "Red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare, full as a flask" |
| What the mnemonic maps to | Flushing, anhidrosis, mydriasis, delirium, hyperthermia and urinary retention |
| Other presenting signs | Tachycardia, absent bowel sounds, confusion, agitation, hallucinations |
| Severe course | Seizures, coma and death if not promptly treated |
| Who is at greatest risk | Patients on several medications with anticholinergic properties, since cumulative burden rises over time; elderly patients, in whom increased blood-brain barrier permeability and reduced central acetylcholine heighten susceptibility |
| First-line management | Supportive care |
| Antidote | Physostigmine, reserved for severe cases: a cholinesterase inhibitor that crosses the blood-brain barrier and reverses both central and peripheral effects; use cautiously given its own risk of cholinergic toxicity |
| Agitation and seizures | Benzodiazepines |
