In conditions where there is narrowing of the airways, such as asthma or chronic obstructive pulmonary disease (COPD, eg emphysema and chronic bronchitis), it is difficult for air to get in and out of the lungs. By opening the airways, salmeterol makes it easier to breathe. Salmeterol doesn’t open the airways as quickly as short-acting beta 2 agonists such as salbutamol or terbutaline, however, it does keep the airways open for much longer. The effects of salmeterol last for about 12 hours, whereas those of salbutamol or terbutaline last for about 3 to 5 hours. This means salmeterol is used to prevent asthma attacks, wheezing, chest tightness or shortness of breath, rather than to relieve them.