Which β-blocker is least likely to worsen asthma symptoms?

Metoprolol is considered the least likely to worsen asthma symptoms because it is a selective beta-1 adrenergic receptor blocker. In contrast, the non-selective beta-blockers, like propranolol, block both beta-1 and beta-2 receptors, which can lead to bronchoconstriction and exacerbate asthma symptoms.

In asthmatic patients, it is essential to avoid non-selective beta-blockers due to their potential to block the beta-2 receptors found in the bronchial smooth muscle, which are responsible for mediating bronchodilation. Metoprolol, by selectively blocking the beta-1 receptors primarily located in the heart, poses a lower risk for causing bronchospastic events compared to non-selective agents.

Labetalol and carvedilol, although they have alpha-blocking activity, still present some beta-blocking effects and are not completely devoid of potential bronchoconstriction risk, specifically through the beta-2 receptor interaction. Therefore, metoprolol stands out as the better option among beta-blockers for patients with a history of asthma or reactive airway disease.