Formoterol hemifumarate is a potent, selective and long-acting β2-adrenoceptor agonist to β2 and β1 receptors with pKd of 8.12 and 5.58, respectively. Formoterol hemifumarate reveals 330-fold selectivity forβ2 over β1 receptors. Formoterol hemifumarate potently relaxes guinea pig trachea (pD2 = 9.29), and is longer-acting and 100-fold more potent than salbutamol. Formoterol hemifumarate 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.
