betablocking

Betablocking, or beta-adrenergic receptor blockade, refers to the action of beta-blockers, drugs that antagonize beta-adrenergic receptors. By blocking beta-1 receptors in the heart, they reduce heart rate, myocardial contractility, and atrioventricular conduction, and decrease renin release from the kidney. Blockade of beta-2 receptors in the lungs and vasculature can cause bronchoconstriction and metabolic effects. At typical doses, some agents are cardioselective for beta-1 while others are non-selective for both beta-1 and beta-2.

Beta-blockers are commonly classified as cardioselective or non-selective. Cardioselective agents include metoprolol, bisoprolol, atenolol, and nebivolol; non-selective agents include propranolol, nadolol, timolol, and pindolol. Some drugs, such as carvedilol and labetalol, block both beta and alpha receptors and can promote vasodilation. Sotalol provides non-selective beta-blockade with additional class III antiarrhythmic activity.

Indications span cardiovascular and other conditions. They are used for hypertension, angina, myocardial infarction, and various arrhythmias, and to treat heart failure with reduced ejection fraction (notably carvedilol, metoprolol succinate, and bisoprolol). Propranolol is used for migraine prophylaxis and certain tremors; beta-blockers may also reduce symptoms of thyrotoxicosis and, off-label, performance anxiety.

Common considerations include potential adverse effects such as bradycardia, fatigue, hypotension, and sexual dysfunction. Non-selective agents can provoke bronchospasm in asthma or COPD. They may mask symptoms of hypoglycemia in diabetes. Abrupt withdrawal should be avoided to prevent rebound tachycardia and hypertension. Contraindications include high-grade heart block, symptomatic bradycardia, and acute decompensated heart failure.