Chapter 202: Anticholinergics

INTRODUCTION

Anticholinergic properties are present in over 600 compounds, including prescription drugs, over-the-counter medications, and plants (Table 202-1). Many of these substances possess anticholinergic activity as either a direct therapeutic effect or as an adverse effect in addition to their primary or predominant pharmacologic effect. Atropine (D,L-hyoscyamine), hyoscyamine, and scopolamine (L-hyoscine) are natural alkaloids that represent prototypical anticholinergic compounds.

Antihistamine (particularly diphenhydramine) overdose is the most common overdose that produces anticholinergic toxicity.¹ Toxicity in children may result from accidental ingestion of an anticholinergic medication, oral administration of hyoscyamine-containing agents to treat colic, topical use of diphenhydramine-containing salves, or therapeutic application of a transdermal hyoscine patch.^2-5 In the elderly, therapeutic doses of one or multiple medications with anticholinergic properties may produce anticholinergic symptoms, or they may simply cause ileus without other anticholinergic findings.^6,7 Ophthalmologic instillation of anticholinergic mydriatics can cause toxicity, especially in the elderly or young children; patients are therefore instructed to lie down and apply 5 minutes of gentle pressure on the nasolacrimal duct when instilling these agents.⁸

Atropine is the antidote for cholinergic syndromes produced from nerve agents or organophosphate insecticides.⁹ Administration of high-dose atropine to someone without cholinesterase poisoning can 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.

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