Terbutaline is a sympathomimetic amine synthesized in the mid-1960's that has been shown by in vitro and in vivo pharmacologic studies in animals to exert a preferential effect on beta 2-adrenergic receptors (beta2-AR), such as those located in bronchial smooth muscle. It has been available for clinical use since the 1970's and has been approved by the FDA for use in the treatment of asthma in children. Terbutaline binds to the beta-2 adrenergic receptor resulting in Gs-protein stimulation which in turn activates adenylyl cyclase increasing intracellular levels of 3'-5' cyclic adenosine monophosphate (cAMP). cAMP then activates protein kinase A (PKA) that phosphorylates several proteins that contribute to smooth muscle relaxation and resultant bronchodilation.