Why are long-acting beta-agonists not used as monotherapy in asthma management?

• A. B2 receptor downregulation
• B. Tachyphylaxis
• C. Hypersensitivity
• D. Mucus hypersecretion

Answer: (A)

Chronic exposure to long-acting beta-agonists leads to desensitization of the beta-2 receptors on airway smooth muscle, meaning the receptors become less responsive and fewer receptors are available on the cell surface. This receptor downregulation underlies tachyphylaxis—a waning bronchodilatory effect with continued use. Because of this loss of efficacy over time, using a LABA alone fails to provide sustained control and can mask worsening inflammation, increasing the risk of severe exacerbations. That’s why LABAs are paired with an inhaled corticosteroid to address the underlying inflammation and preserve efficacy. The other options don’t capture the central pharmacologic reason: hypersensitivity and mucus hypersecretion aren’t the key drivers of why LABAs shouldn’t be used alone, and while tachyphylaxis is related, the specific mechanism is beta-2 receptor downregulation.