Cardiovascular · Medicine Class
Competitive antagonism of beta-adrenergic receptors
Beta blockers competitively antagonize the effects of catecholamines (epinephrine, norepinephrine) at beta-adrenergic receptors. Beta-1 receptors in the heart mediate increased heart rate (chronotropy) and contractility (inotropy). Beta-2 receptors in the lungs mediate bronchodilation; in blood vessels, vasodilation. Beta-1 selective blockers (cardioselective) preferentially block cardiac receptors at standard doses, minimizing bronchoconstriction. Non-selective blockers block both beta-1 and beta-2.
Metoprolol succinate (Toprol-XL)
Beta-1 selective; once-daily XL formulation; first-line in HF and post-MI. Avoid immediate-release in HF decompensation.
Carvedilol (Coreg)
Non-selective + alpha-1 blocker; proven mortality reduction in HFrEF (COPERNICUS, CAPRICORN). Twice daily.
Bisoprolol (Zebeta)
Highest beta-1 selectivity; once daily. CIBIS-II trial: 34% mortality reduction in HFrEF.
Atenolol (Tenormin)
Beta-1 selective; hydrophilic (less CNS penetration — fewer nightmares). Widely used for hypertension.
Propranolol (Inderal)
Non-selective; lipophilic; crosses BBB (effective for migraine, tremor, anxiety). Multiple daily dosing.
Labetalol (Trandate)
Non-selective beta + alpha-1 blocker; preferred for hypertension in pregnancy; IV form for hypertensive emergency.
Calcium channel blockers (diltiazem, verapamil) — additive negative chronotropy/inotropy → heart block
Digoxin — additive bradycardia and AV block
Clonidine — rebound hypertension worsened; stop beta-blocker before clonidine
Insulin/sulfonylureas — mask tachycardia of hypoglycemia
MAOIs — hypertensive crisis risk (with non-selective beta-blockers)
Cardioselective beta-1 blockers (metoprolol, bisoprolol, atenolol) have a better safety profile in mild-moderate asthma than non-selective agents, but still carry some bronchoconstriction risk. In severe or uncontrolled asthma, all beta-blockers are generally avoided. When strongly indicated (post-MI, HFrEF), a cardioselective agent at low dose can be used with careful monitoring.
No — abrupt discontinuation of beta-blockers can cause rebound tachycardia, angina, hypertension, and myocardial infarction (especially dangerous in coronary artery disease). Beta-blockers should always be tapered over 1-2 weeks when discontinuation is necessary. This rebound occurs because chronic blockade upregulates beta-adrenergic receptors.