Metoprolol is preferred over propranolol in some patients because it

Propranolol is a nonselective blocker of beta adrenoceptors, whereas metoprolol is b1 -selective. Metoprolol is less likely to block receptors in the bronchiolar smooth muscle and is less likely to cause bronchoconstriction, especially in asthmatic patients. Propranolol and metoprolol are considered to be equally effective as antiarrhythmics and in post-MI prophylaxis, and both are cardiodepressant. Drugs that appear to have both alpha- and beta-blocking actions include carvedilol and labetalol.