Muscarinic antagonists poisoning

In contrast to muscarine, atropine blocks these actions of acetylcholine and muscarine. Atropine is, therefore, an acetylcholine antagonist. It binds where acetylcholine binds and therefore prevents the binding of the latter but does not activate it. Two molecules cannot occupy the same binding site at the same time. Atropine is isolated from the plant Atropa belladonna. Extracts of this plant have been used for millennia for a variety of purposes. Although large doses are poisonous (Atropos is the name of the Fate who cuts the thread of life), small doses causes dilation of the pupils, a consequence of its action as an acetylcholine antagonist, and has been used for cosmetic purposes by women, hi Itahan, belladonna means beautiful woman. 

Atropine Nonselective competitive antagonist at all muscarinic receptors in CNS and periphery Blocks muscarinic excess at exocrine glands, heart, smooth muscle Mandatory antidote for severe cholinesterase inhibitor poisoning Intravenous infusion until antimuscarinic signs appear continue as long as necessary Toxicity Insignificant as long as AChE inhibition continues... 

Atropine is a competitive antagonist of muscarine at the cholinergic receptors and is, therefore, antidotal in these types of poisonings. Doses sufficient to reverse the effects of excessive pulmonary secretions and bradycardia should be administered. Activated charcoal may be useful in recent ingestions, but because most patients have vomiting and diarrhea, its usefulness is limited and unproved. 

Of direct relevance for pesticide science is the antagonist atropine. This toxicant also binds specifically to the muscarinic receptors where it blocks the effect of ACh. The symptoms are therefore the opposite of those caused by muscarine or acetylcholine (pupil dilation, dry mouth, inhibition of sweating, tachycardia, palpitations, hallucinations, delirium, etc.). Atropine is an important antidote when one is poisoned with a cholinesterase-inhibiting insecticide. 

The cardiovascular effects of muscarinic receptor antagonists are of limited clinical application. Atropine may be considered in the initial treatment of patients with acute myocardial infarction in whom excessive vagal tone causes sinus or nodal bradycardia. Dosing must be judicious doses that are too low can cause a paradoxical bradycardia excessive doses will cause tachycardia that may extend the infarct by increasing demand. Atropine occasiormlly is useful in reducing the severe bradycardia and syncope associated with a hyperactive carotid sinus reflex. Atropine will protect the SA and AV nodes from the effects of excessive ACh in instances of poisoning with anticholinesterase pesticides. 

POISONING BY MUSCARINIC RECEPTOR ANTAGONISTS AND OTHER DRUGS WITH ANTICHOLINERGIC PROPERTIES... 

The deliberate or accidental ingestion of natural belladonna alkaloids is a major cause of poisonings. Many histamine Hj-receptor antagonists, phenothiazines, and tricyclic antidepressants also block muscarinic receptors, and in sufficient dosage, produce syndromes that include features of atropine intoxication. 

Of the anticholinergics, atropine is the drug most frequently used for the treatment of human poisoning. This muscarinic cholinergic antagonist acts by blocking the overstimulating effects of acetylcholine at the muscarinic... 

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