What are long-acting beta-2 agonists and why should they not be used alone?

Long-acting beta-2 agonists, or LABAs, like salmeterol and formoterol provide sustained bronchodilation lasting 12 hours and are used as add-on controller therapy for asthma and chronic obstructive pulmonary disease. LABAs must never be used alone for asthma because an FDA black box warning found increased asthma-related death risk when used without an inhaled corticosteroid. They are always prescribed in combination inhalers with an ICS, such as fluticasone-salmeterol or budesonide-formoterol. LABAs are not rescue medications and should not be used for acute bronchospasm.