Salmeterol (sold in China as Qitai) is a long-acting β2 adrenergic receptor agonist (LABA) used in the maintenance and prevention of asthma symptoms and maintenance of chronic obstructive pulmonary disease (COPD) symptoms. Symptoms of bronchospasm include shortness of breath, wheezing, coughing and chest tightness. It is also used to prevent breathing difficulties during exercise (exercise-induced bronchoconstriction). It was patented in 1983 and came into medical use in 1990. It is marketed as Serevent in the US. It is available as a dry-powder inhaler (DPI) that releases a powdered form of the drug. It was previously available as a metered-dose inhaler (MDI) but was discontinued in the US in 2002. It is available as an MDI in other countries as of 2020. Mechanism of action Inhaled salmeterol belongs to a group of drugs called beta-2 agonists. These drugs stimulate beta-2 receptors present in the bronchial musculature. This causes them to relax and prevent the onset and worsening of symptoms of asthma. They act on the enzyme adenyl cyclase which increases the concentration of cAMP (Cyclic adenosine monophosphate). This cyclic AMP decreases the smooth muscle tone. This drug is 10,000-times more lipid soluble than the short acting beta-2 adrenoceptor agonist, albuterol. Unlike albuterol, salmeterol becomes dissolved in the lipid bilayer of the cell membrane, and its gradual dissociation from the cell membrane provides beta-2 adrenoceptors with a supply of agonist for an extended period of time. The primary noticeable difference of salmeterol from salbutamol, and other short-acting β2 adrenoreceptor agonists (SABAs), is its duration of action. Salmeterol lasts approximately 12 hours in comparison with salbutamol, which lasts about 4–6 hours. When used regularly every day as prescribed, inhaled salmeterol decreases the number and severity of asthma attacks. Formoterol has been demonstrated to have a faster onset of action than salmeterol as a result of a lower lipophilicity, and has also been demonstrated to be more potent—a 12 µg dose of formoterol has been demonstrated to be equivalent to a 50 µg dose of salmeterol. Medical uses Salmeterol is used in moderate-to-severe persistent asthma following previous treatment with a short-acting β2 adrenoreceptor agonist (SABA) such as salbutamol (albuterol). LABAs should not be used as a monotherapy, instead, they should be used concurrently with an inhaled corticosteroid, such as beclometasone dipropionate or fluticasone propionate in the treatment of asthma to minimize serious reactions such as asthma-related deaths. Combination of inhaled corticosteroids and salmeterol (LABA)