## **Core Concept**
The question revolves around a drug that causes severe bronchospasm as a significant side effect, leading to its cessation in clinical use. This scenario is commonly associated with non-selective beta-blockers, particularly those with a higher affinity for beta-2 adrenergic receptors.

## **Why the Correct Answer is Right**
Propranolol, a non-selective beta-blocker, blocks both beta-1 and beta-2 adrenergic receptors. Beta-2 receptors are predominantly found in the smooth muscle of the bronchi, and their blockade can lead to bronchoconstriction. This is particularly problematic in patients with asthma or chronic obstructive pulmonary disease (COPD), as it can precipitate severe bronchospasm. The use of propranolol in such patients is contraindicated, and its administration can indeed be stopped or avoided due to this severe side effect.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Atenolol is a beta-1 selective beta-blocker. While it can still cause bronchospasm, its beta-1 selectivity means it is less likely to cause severe bronchospasm compared to non-selective beta-blockers like propranolol, especially at lower doses.
- **Option B:** Metoprolol is also a beta-1 selective beta-blocker, similar to atenolol. Its use is less likely to be stopped due to bronchospasm compared to non-selective agents.
- **Option D:** Labetalol has both alpha-1 and non-selective beta-blocking activity. While it can cause bronchospasm due to its beta-blocking effects, it is not as commonly associated with severe bronchospasm as a pure non-selective beta-blocker like propranolol.

## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that in patients with asthma or COPD, beta-1 selective blockers (e.g., metoprolol, atenolol) are preferred over non-selective beta-blockers when beta-blockade is necessary, to minimize the risk of inducing bronchospasm.

## **Correct Answer:** . Propranolol