Chapter 202: Anticholinergics

INTRODUCTION

Approximately 620 compounds have anticholinergic properties, 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 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, administration of hyoscyamine-containing agents to treat colic, the topical use of diphenhydramine-containing salves, and therapeutic application of a transdermal hyoscine patch.^2,3,4,5 In the elderly, therapeutic doses of one or multiple medications with anticholinergic properties may produce anticholinergic symptoms or ileus without all the signs of the anticholinergic toxidrome.^6,7 Ophthalmologic instillation of anticholinergic mydriatic agents can cause toxicity, especially in the elderly or young children; thus patients are 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 a cholinergic syndrome produced from a nerve agent or an organophosphate insecticide.⁹ Use of high-dose atropine by someone without cholinesterase poisoning may result in anticholinergic toxicity within 1 hour. 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 producing toxicity 1 to 4 hours after ingestion or sooner if smoked. Alkaloid plants are abused for their hallucinogenic effects.^11,12 Group anticholinergic plant poisonings 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 been reported.^15,16 Ingestion ...