Why is the chronic use of long-acting beta agonists (LABAs) alone without the concomitant use of an inhaled corticosteroid contraindicated in asthma? What about short-acting beta agonists (SABAs), can they be used without taking an inhaled corticosteroid at the same time?
Activation of β2-adrenoceptor promotes bronchodilation. β2-adrenoceptor agonists are the most potent bronchodilators in current clinical use. Inhaled short-acting beta agonists (SABAs), for example salbutamol (known as albuterol in the USA) have a bronchodilator effect that lasts for 4 to 6 hours, while long-acting beta agonists (LABAs), for example salmeterol, have a bronchodilator effect that lasts for 12 to 24 hours (depending upon the drug). SABAs are used to relieve acute bronchoconstriction. Use of a SABA can be a life-saving intervention during an asthma attack. In contrast, LABAs are used chronically to mainain bronchodilation improving airway function and controlling occurance of symptoms.
Chronic use of LABAs causes tolerance due to downregulation of β2-adrenoceptors. This is associated with an increased risk of mortality in patients with asthma. Therefore the use of LABAs alone is contraindicated. The downregulation of β2-adrenoceptors by chronic use of LABAs can impair the response to SABAs when they are need for acutre relief of symptoms during an asthma attack.