Which type of beta-blocker is contraindicated in patients with asthma?

Nonselective beta-blockers are contraindicated in patients with asthma primarily because they block both beta-1 and beta-2 adrenergic receptors. While beta-1 receptors are primarily located in the heart and mediate cardiac effects, beta-2 receptors are found in the lungs and play a crucial role in bronchodilation. When nonselective beta-blockers are administered, the blockade of beta-2 receptors can lead to bronchoconstriction, exacerbating asthma symptoms and potentially leading to severe respiratory distress.

In contrast, cardioselective beta-blockers primarily target beta-1 receptors and have a lesser effect on beta-2 receptors. This selectivity makes them generally safer for use in patients with asthma, as they are less likely to provoke bronchospasm. Alpha/beta-blockers also have a mixed mechanism, but their use in asthma can vary depending on the specific medication and its properties.

Hence, the contraindication of nonselective beta-blockers in asthma patients is closely related to their potential to cause or worsen bronchoconstriction.