Salmeterol is a bronchodilator. It works by relaxing muscles in the airways to improve breathing. Salmeterol inhalation is used to prevent asthma attacks. It will not treat an asthma attack that has already begun. Salmeterol inhalation is also used to treat chronic obstructive pulmonary disease (COPD) including emphysema and chronic bronchitis. Salmeterol inhalation may also be used for other purposes not listed in this medication guide.