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An anticholinergic is a substance that antagonizes the action of the neurotransmitter acetylcholine. A large number of pharmaceuticals and substances found in plants possess anticholinergic activity (Table 196-1). Atropine (D,L-hyoscyamine), hyoscyamine, and scopolamine (L-hyoscine) are natural alkaloids that represent prototypical anticholinergic compounds. An important principle of anticholinergic toxicity is that many substances possess anticholinergic activity, either as a direct therapeutic effect or an adverse effect, in addition to their primary or predominant pharmacologic effect.

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Table 196-1 Major Groups of Substances with Anticholinergic Activity
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Antihistamines (particularly diphenhydramine) are the most common overdose that produces anticholinergic toxicity. Young children may accidentally ingest a few pills, such as orphenadrine, that can cause toxicity from its anticholinergic properties.1 Other examples of pediatric exposures causing anticholinergic toxicity include hyoscyamine-containing agents to treat colic, the topical use of diphenhydramine-containing salves, and therapeutic application of a transdermal hyoscine patch.2–5 Conversely, in the elderly, therapeutic doses of one or multiple medications with anticholinergic properties may produce anticholinergic toxicity.6,7 In addition, ophthalmologic instillation of anticholinergic mydriatic agents can cause toxicity, especially in the elderly.8

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Atropine is the antidote for a cholinergic syndrome produced from a nerve agent or an organophosphate insecticide.9 Use of high-dose atropine by someone who is not suffering from the effects of cholinesterase poisoning may result in anticholinergic toxicity. This occurred in Israel during the first Gulf War in 1991 when frightened civilians dosed themselves with atropine fearing an incoming Scud missile chemical weapon attack.

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Plant poisonings may result in an anticholinergic toxidrome. In Taiwan, the anticholinergic toxidrome is most commonly associated with single-plant exposures.10 Belladonna alkaloid-containing plants have potent anticholinergic effects producing toxicity 1 to 4 hours postingestion or sooner if smoked. Alkaloid plants are abused for their hallucinogenic effects.11,12 Group anticholinergic plant ingestions are common in adolescents seeking these psychoactive hallucinogenic effects.13,14 Inadvertent poisoning from the ingestion of belladonna-contaminated herbal teas and Chinese traditional medicines has also been reported.15,16 Ingestion of seeds and berries, sometimes due to ...

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