An advantage of Salmeterol over Isoproterenol in the treatment of bronchial asthma is that Salmeterol:

• A. is more selective for β2 adrenergic receptors
• B. has more β-agonist activity than Isoproterenol
• C. has a more rapid onset of action
• D. has an action against cardiogenic shock

Answer: (A)

The main idea here is how receptor selectivity shapes the usefulness and safety of beta-agonists in asthma. Salmeterol is a long-acting beta-2 (β2) adrenergic receptor agonist, so it mainly targets receptors in bronchial smooth muscle to produce bronchodilation with minimal stimulation of the heart. Isoproterenol, on the other hand, is non-selective and activates both β1 (heart) and β2 receptors. That means while it can open airways, it also stimulates the heart, causing tachycardia and other unwanted beta-1 effects, which is not ideal for chronic asthma management. Because of its higher β2 selectivity, salmeterol provides effective bronchodilation with fewer cardiac side effects, making it a better option for ongoing control of asthma. (Note: its onset is slower and it’s used for maintenance, not acute relief.)