Sepracor in the US is developing arformoterol [R,R-formoterol], a single isomer form of the beta(2)-adrenoceptor agonist formoterol [eformoterol]. This isomer contains two chiral canters and is being developed as an inhaled preparation for the treatment of respiratory disorders. Sepracor believes that arformoterol has the potential to be a once-daily therapy with a rapid onset of action and a duration of effect exceeding 12 hours. Sepracor stated in July 2003 that it had completed more than 100 preclinical studies and initiated or completed 15 clinical studies for arformoterol inhalation solution for the treatment of bronchospasm in patients with COPD. The pharmacologic effects of beta2-adrenoceptor agonist drugs, including arformoterol, are at least in part attributable to stimulation of intracellular adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3′,5′-adenosine monophosphate (cyclic AMP). Increased intracellular cyclic AMP levels cause relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells. In vitro tests show that arformoterol is an inhibitor of the release of mast cell mediators, such as histamine and leukotrienes, from the human lung. Arformoterol also inhibits histamine-induced plasma albumin extravasation in anesthetized guinea pigs and inhibits allergen-induced eosinophil influx in dogs with airway hyper-responsiveness. The relevance of these in vitro and animal findings to humans is unknown.