Introduction
This topic covers acute poisoning with atropine and other drugs with strong antimuscarinic action, such as belladonna alkaloids, scopolamine and some antihistamines. It concerns recognising the anticholinergic toxidrome, understanding its basic pharmacology, and the emergency management expected in the first hours of care.
Pharmacology and sources
Atropine is a tropane alkaloid found in Atropa belladonna, Datura species and Hyoscyamus. Clinically it is used for bradycardia, as premedication before anaesthesia, in ophthalmology and in the treatment of organophosphate poisoning. Because it is lipophilic, it is absorbed quickly from the gut, mucosa and conjunctiva and crosses the blood-brain barrier, so central effects are prominent. It is mainly eliminated by the kidneys, with a half-life of a few hours, and effects may last longer in severe poisoning.
Mechanism
Atropine is a competitive antagonist at muscarinic acetylcholine receptors (M1 to M5). Blocking them removes parasympathetic effects on the eye, heart, bronchial smooth muscle, glands, gut and bladder. Sweat glands are cholinergic but sympathetically innervated, so blockade stops sweating. In the brain, M1 blockade disturbs attention, memory and orientation. Toxicity therefore results from excessive muscarinic blockade, and it is reversed by raising acetylcholine levels at the receptor, which is the rationale for physostigmine.