Bronchodilator drugs are usually administered by inhalation. They are used to relieve symptoms in obstructive lung disease, such as in asthma or COPD. Short-acting bronchodilators are effective within minutes, for up to 6-8 hours. Such drugs are very useful when used by the patient ‘if needed’. Long-acting bronchodilator drugs are effective for 12 or more hours. They are usually administered to patients who use inhaled corticosteroids, for example to relieve nocturnal airway obstruction.
Bronchodilators relax smooth muscles in a contractile state. This induces acute bronchodilatation, which can be assessed for example by spirometry. In the absence of increased smooth muscle tone, or if inflammatory mechanisms predominate, bronchodilator drugs have little effect. On that account bronchodilators are usually least effective in patients with either a normal or a very low FEV1.
Bronchodilators are suitable for relieving increased smooth muscle tone as well as in preventing it from occurring. Hence they may be used to protect against the effects of bronchoconstricting stimuli, such as exercise or exposure to allergens.
Please note that historically the effectiveness of a bronchodilator drug has been tested by looking at improvements in the FEV1. However, in severe COPD clinically relevant improvements occur in the VC even if the FEV1 does not improve.