atropine

Atropine is a tropane alkaloid used in medicine to counteract muscarinic acetylcholine receptor–mediated effects. It is derived from Atropa belladonna and other plants in the Solanaceae family. In pharmacology, atropine acts as a competitive antagonist at muscarinic receptors (M1–M5), thereby inhibiting parasympathetic nerve impulses.

The physiological effects of atropine are dose-dependent and tissue-specific. It increases heart rate by blocking vagal influences on the sinoatrial node, decreases secretions from salivary, bronchial, and gastric glands, and reduces gastrointestinal smooth muscle tone. It can cause pupil dilation and cycloplegia when applied topically to the eye. At higher doses, central effects such as agitation or delirium may occur.

Clinical uses include treatment of symptomatic bradycardia and as an antidote for organophosphate and nerve agent poisoning. It is also used preoperatively to reduce airway and GI secretions and in ophthalmology to induce mydriasis and paralysis of accommodation for eye examination or surgery.

Contraindications include narrow-angle glaucoma, certain tachyarrhythmias, ileus or urinary retention due to obstructive uropathy, and hypersensitivity to atropine. Caution is advised in the elderly and in patients with cognitive impairment or severe systemic illness.

Common adverse effects are dry mouth, blurred vision with photophobia, difficulty urinating, constipation, tachycardia, and confusion. Pharmacokinetically, atropine can be administered orally, intravenously, intramuscularly, or topically; it is well absorbed, distributes widely including the central nervous system, and is metabolized by the liver with renal excretion.