A 62-year-old man with mild asthma needs a beta-blocker after a myocardial infarction. Which property of the prescribed drug best minimises the risk of precipitating bronchospasm?
- A Intrinsic sympathomimetic activity
- B Beta-1 cardioselectivity ✓
- C Alpha-1 blocking activity
- D Nitric oxide mediated vasodilation
Correct answer: B. Beta-1 cardioselectivity
Explanation
Bronchial smooth muscle tone is regulated mainly by beta-2 receptors, so blockade of these receptors can trigger bronchospasm in asthmatics. Cardioselective agents such as atenolol and metoprolol preferentially occupy beta-1 receptors at therapeutic doses and spare bronchial beta-2 receptors, making them relatively safer in reactive airway disease, though caution is still advised. Nitric oxide release by nebivolol affects vessels, and intrinsic sympathomimetic activity relates to resting heart rate rather than airway safety.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
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