atropina

Atropine, also called atropina in some languages, is a tropane alkaloid derived from plants of the Solanaceae family, including Atropa belladonna. It is the racemic mixture of hyoscyamine and acts as a competitive antagonist of muscarinic acetylcholine receptors (M1–M5), thereby reducing parasympathetic activity.

Pharmacologic effects include pupil dilation (mydriasis) with loss of accommodation, decreased secretions from the salivary and bronchial glands, relaxation of bronchial smooth muscle, reduced gastrointestinal motility, and an increased heart rate. Central nervous system effects occur at higher doses and can include agitation, confusion, and delirium. The intensity and duration of effects depend on dose and route of administration.

Medical uses of atropine include preoperative reduction of secretions, adjunctive treatment to manage bradycardia, and facilitation of ocular examination or surgery via mydriasis and cycloplegia. It is also used as an antidote in cases of organophosphate or other anticholinesterase poisoning, counteracting muscarinic overstimulation; it is typically given with pralidoxime, which reactivates acetylcholinesterase. Historically and in some settings, atropine has been used to treat certain gastrointestinal and biliary disorders, though these uses are now less common.

Pharmacokinetics and administration vary by route: atropine can be given orally, intramuscularly, intravenously, or as ophthalmic eye drops. It is well absorbed systemically and crosses the blood–brain barrier at higher exposures; duration of action is relatively long compared with some antimuscarinics, often lasting several hours to days depending on the effect and dose. Metabolism occurs hepatically, with renal excretion of metabolites.

Contraindications include narrow-angle glaucoma, certain types of tachyarrhythmia, pyloric or urinary tract obstruction, and severe dry mouth with dehydration. Caution is advised in the elderly, pregnant or breastfeeding individuals, and in patients with GI obstruction or cognitive impairment.