Formoterol is a long-acting β2 agonist (LABA) that has an extended duration of action (up to 12 hours) compared to short-acting β2 agonists such as salbutamol, which are effective for 4–6 hours. LABAs such as formoterol are used as "symptom controllers" to supplement prophylactic corticosteroid therapy (e.g., fluticasone). A "reliever" short-acting β2 agonist (e.g., salbutamol) is still required, since LABAs are not recommended for the treatment of acute asthma. Inhaled formoterol works like other β2 agonists, causing bronchodilation by relaxing the smooth muscle in the airway so as to treat the exacerbation of asthma. The long duration of formoterol action occurs because the formoterol molecules initially diffuse into the plasma membrane of the lung cells, and then are slowly released back outside, where they can come into contact with β2 adrenergic receptors.
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