Terbutaline Sulfate

Terbutaline is a relatively selective β2-adrenergic bronchodilator, with little or no effect on alpha-adrenergic receptors. It has a preferential effect on β2-adrenergic receptors, but it stimulates beta-adrenergic receptors less selectively than the relatively selective β2-agonists do. Terbutaline appears to act more strongly on the beta-receptors of bronchial, vascular and uterine smooth muscle (β2 receptors) than on the beta-receptors of the heart (β1 receptors). The medicine relaxes smooth muscle and inhibits uterine contractions, but it may also cause some cardiostimulatory effects and CNS stimulation. Its pharmacologic effects are at least in part due to stimulation, through beta-adrenergic receptors, of intracellular adenyl cyclase. This is the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3',5'-adenosine monophosphate (c-AMP). Higher c-AMP levels are associated with relaxation of bronchial smooth muscle and with inhibition of the release of mediators of immediate hypersensitivity from cells, especially mast cells.