Metoprolol is preferred over Propranolol as it: September 2010
**Core Concept**
Metoprolol is a selective beta-1 adrenergic receptor blocker, primarily acting on the heart, whereas propranolol is a non-selective beta-blocker affecting both beta-1 and beta-2 receptors. This selectivity influences its clinical use, especially in conditions like hypertension and angina where cardiac effects are desired without bronchial or peripheral vasodilatory side effects.
**Why the Correct Answer is Right**
Metoprolol has higher affinity and selectivity for beta-1 receptors (found predominantly in the heart) compared to propranolol. This means it more effectively reduces heart rate, cardiac output, and myocardial oxygen demand with minimal effects on beta-2 receptors in the lungs or blood vessels. Its selectivity reduces the risk of bronchoconstriction and hypotension, making it safer in patients with asthma or chronic obstructive pulmonary disease (COPD).
**Why Each Wrong Option is Incorrect**
Option B: Propranolol blocks beta-2 receptors more than metoprolol, not less. Metoprolol’s selectivity makes it *less* effective at blocking beta-2 receptors, so this statement is false.
Option C: Propranolol is more effective in suppressing essential tremors than metoprolol; metoprolol has weaker antitremor effects.
Option D: Metoprolol does not impair exercise capacity; in fact, it may improve exercise tolerance by reducing cardiac workload, unlike non-selective agents that can cause fatigue or reduced performance.
**Clinical Pearl / High-Yield Fact**
Always remember: **Metoprolol > Propranolol in beta-1 selectivity** — this makes it the preferred choice in cardiac conditions, especially in patients with asthma or COPD.
✓ Correct Answer: A. Is more potent in blocking beta-1 receptors