NCIt definition : A phenothiazine derivative with antiemetic and antihistaminic properties. Promethazine
antagonizes the central and peripheral effects of histamine mediated by histamine
H1 receptors. The effects include bronchoconstriction, vasodilation and spasmodic
contractions of gastrointestinal smooth muscle. In addition, this agent binds to muscarinic
receptors, resulting in anticholinergic and antiemetic activities.;