<p>Formoterol fumarate is a long-acting &beta;2-adrenergic receptor agonist (&beta;2-agonist). Inhaled formoterol fumarate acts locally in the lung as a bronchodilator. In vitro studies have shown that formoterol has more than 200-fold greater agonist activity at &beta;2-receptors than at &beta;1-receptors. Although &beta;2-receptors are the predominant adrenergic receptors in bronchial&nbsp;smooth muscle&nbsp;and &beta;1-receptors are the predominant receptors in the heart, there are also &beta;2-receptors in the human heart comprising 10%-50% of the total beta-adrenergic receptors. The precise function of these receptors has not been established, but they raise the possibility that even highly selective &beta;2-agonists may have cardiac effects.<br />
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The pharmacologic effects of &beta;2-adrenoceptor agonist drugs, including formoterol, are at least in part attributable to stimulation of&nbsp;intracellular&nbsp;adenyl cyclase, the&nbsp;enzyme&nbsp;that catalyzes the conversion of&nbsp;adenosine triphosphate&nbsp;(ATP) to cyclic-3&#39;, 5&#39;-adenosine monophosphate (cyclic AMP). Increased cyclic AMP levels cause relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.<br />
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In vitro tests show that formoterol is an inhibitor of the release of&nbsp;mast cell&nbsp;mediators, such as histamine and leukotrienes, from the human lung. Formoterol 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&nbsp;in vitro&nbsp;and animal findings to humans is unknown.</p>