Meluadrine (Hoku 81) is a beta-adrenergic receptor agonist with tocolytic activity. Meluadrine binds to and activates beta-2 adrenergic receptors of myometrial smooth muscle in the uterus, thereby activates adenyl cyclase, an enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3',5'-adenosine monophosphate (cAMP). Increased cAMP levels leads to a reduction in intracellular calcium concentration, thereby causes smooth muscle relaxation and decreases the intensity of uterine contractions. Meluadrine is a bronchodilator, and one of the metabolites of tulobuterol. Meluadrine was approximately 8 times more potent than tulobuterol, approximately twice as potent as salbutamol, and approximately as potent as isoprenaline in relaxing effect on the isolated tracheal smooth muscle preparation of guinea pigs.