Beta-2 receptor agonists relax airway smooth muscle and are central bronchodilators for asthma and COPD. They differ mainly by onset and duration rather than by an absolute difference in receptor selectivity.

Beta-2 receptors couple to Gs and increase cyclic AMP, promoting smooth-muscle relaxation. In skeletal muscle and liver, beta-2 stimulation contributes to tremor, glycogenolysis, insulin release and intracellular potassium shift.

Salbutamol, terbutaline, formoterol, salmeterol, indacaterol, olodaterol and vilanterol are important examples. Ritodrine is an older uterine relaxant with limited use.

Short-acting inhaled beta-2 agonists provide rapid relief of bronchospasm. Long-acting agents are maintenance bronchodilators; in asthma they are used within an inhaled-corticosteroid-containing strategy, while COPD regimens follow symptom and exacerbation assessment.

Tremor, palpitations, tachycardia, nervousness, headache, hyperglycaemia and hypokalaemia may occur. Excessive use can cause arrhythmia and lactic acidosis and may signal poorly controlled airway disease.

Use cautiously in significant tachyarrhythmia, unstable cardiovascular disease, hyperthyroidism and hypokalaemia. Long-acting beta-2 agonist monotherapy is not appropriate controller treatment for asthma.