Atropine is a naturally occurring tropane alkaloid extracted from plants of the family Solanaceae including deadly nightshade (A. belladonna). It is a non-selective, competitive antagonist of the muscarinic acetylcholine receptor types M1, M2, M3, M4, and M5 (pKBs range from 8.9-9.8). Atropine increases firing of the sinoatrial node and conduction through the atrioventricular node of the heart, opposes the actions of the vagus nerve, blocks acetylcholine receptor sites, and decreases bronchial secretions. It is classified as an anticholinergic (parasympatholytic) drug and commonly used to dilate the pupils, increase heart rate, reduce salivation and other secretions, and as an antidote against organophosphate poisoning.
