Aformoterol is the (R,R)-enantiomer of the β-adrenergic receptor (β-AR) agonist formoterol . It selectively binds to β- over β-ARs (Ks = 2.9 and 113 nM, respectively) as well as β-adrenergic, B bradykinin, neurokinin 1 (NK) and NK receptors when used at concentrations up to 3 μM. Aformoterol induces cAMP accumulation in cultured human bronchial epithelial cells. Ex vivo, aformoterol (0.01-1,000 nM) induces dose-dependent relaxation of guinea pig tracheal strips precontracted with carbamoylcholine , ovalbumin, or histamine (pDs = 8.4, 9.5, and 9.5, respectively). In vivo, aformoterol reverses histamine- and ovalbumin-induced bronchoconstriction in guinea pigs (EDs = 1 and 40 nmol/kg, respectively). Formulations containing aformoterol have been used in the treatment of chronic obstructive pulmonary disease (COPD).