Which of the following beta blockers is cardioselective (β₁-selective) and is therefore the preferred agent in patients with concurrent asthma or COPD?

Explanation

## Cardioselective (β₁-Selective) Beta Blockers **Key Point:** Cardioselective beta blockers preferentially block β₁ receptors on the heart at therapeutic doses, sparing β₂ receptors in bronchial and vascular smooth muscle. This selectivity is dose-dependent and is lost at higher doses. ### Cardioselective Beta Blockers Bisoprolol is a highly selective β₁ blocker with the highest cardioselectivity among commonly used agents: - **Bisoprolol** (very high selectivity, β₁/β₂ ratio ~170:1) - **Atenolol** (high selectivity, β₁/β₂ ratio ~74:1) - **Metoprolol** (moderate selectivity, β₁/β₂ ratio ~26:1) - **Acebutolol** (moderate selectivity, β₁/β₂ ratio ~7:1) ### Why Cardioselectivity Matters in Respiratory Disease **High-Yield:** Non-selective beta blockers block β₂ receptors on bronchial smooth muscle, causing: - Bronchoconstriction - Increased airway resistance - Exacerbation of asthma and COPD Cardioselective agents at therapeutic doses preserve β₂-mediated bronchodilation. ### Comparison Table | Agent | Selectivity | β₁/β₂ Ratio | Safe in Asthma/COPD | | --- | --- | --- | --- | | Propranolol | Non-selective | 1:1 | No | | Nadolol | Non-selective | 1:1 | No | | Bisoprolol | β₁-selective | ~170:1 | Yes (preferred) | | Carvedilol | Non-selective (α + β blocker) | 1:1 | No | **Clinical Pearl:** Even cardioselective agents should be used with caution in severe asthma or COPD. If a beta blocker is essential, bisoprolol or atenolol at the lowest effective dose is preferred, with concurrent bronchodilators available. **Warning:** Carvedilol is a combined α and β blocker with non-selective beta-blocking properties and is NOT suitable for asthma/COPD patients.