About salmeterola long-acting beta2-adrenergic agonist, phenethylamine derivative, bronchodilator(antiasthma).mechanism of action of salmeterolsalmeterol is a long acting ?2 receptor agonist. it directly relaxes the airway smooth muscles and produces bronchodilation. stimulation of ?2 receptors activates gs adenylyl-cyclase -cyclic amp path way and produces reduction in smooth muscle tone. ?2 receptor agonists also increases the conductance of large ca2+ sensitive k+ channels in airway smooth muscles and leads to membrane hyperpolarisation and relaxation of smooth muscles. its ?2 receptor selectivity is about 50 times greater than salbutamol. ?2 receptor agonists also suppress the release of leukotrienes and histamine from the mast cells in the lung tissue and enhance mucociliary function and decrease micro vascular permeability and also inhibits phospholipase a2 which produces inhibition of prostaglandins production.