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Pharmacology · single question

A patient on salmeterol for asthma asks about its mechanism of action. Which BEST describes salmeterol's MOA?

  1. Long-acting beta-2 adrenergic agonist causing bronchodilation
  2. Phosphodiesterase inhibitor
  3. Muscarinic receptor antagonist (anticholinergic)
  4. Short-acting beta-1 adrenergic agonist
Show answer and explanation

Correct answer: A. Long-acting beta-2 adrenergic agonist causing bronchodilation

  • A. Correct. Salmeterol is a long-acting beta-2 adrenergic agonist (LABA). It selectively binds beta-2 receptors in bronchial smooth muscle, causing relaxation and bronchodilation. Unlike albuterol (short-acting), salmeterol provides 12-hour bronchodilation and is used for maintenance, not rescue.
  • B. Phosphodiesterase inhibitors (e.g., theophylline) prevent cAMP breakdown; not the mechanism of salmeterol.
  • C. Muscarinic antagonists (e.g., ipratropium, tiotropium) block acetylcholine-mediated bronchoconstriction — a different mechanism from beta-2 agonism.
  • D. Beta-1 adrenergic agonists primarily act on the heart (increased rate and contractility); salmeterol is selective for beta-2 (pulmonary) receptors.

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