Propantheline bromide (Pro-Banthine) competitively antagonizes acetylcholine activity mediated by muscarinic receptors at neuroeffector sites on smooth muscle and exocrine gland cells. Propantheline Bromide is the bromide salt form of propantheline, a quaternary ammonium compound structurally related to belladonna alkaloids. An aspartic acid residue present in the N-terminal portion of the third transmembrane helix of the muscarinic receptor is believed to form an ionic bond with the tertiary or quaternary nitrogen of the antagonist. Antagonism leads to a reduction of exocrine glands secretions and to relax the bronchial muscle and reduce tone and motility of intestinal smooth muscle.