Betablocker

A beta-blocker, or beta-adrenergic blocker, is a drug that antagonizes beta-adrenergic receptors, reducing the effects of adrenaline and other catecholamines. They decrease heart rate, reduce myocardial contractility, and can inhibit renin release, thereby lowering blood pressure and myocardial oxygen demand.

Beta-blockers are categorized by receptor selectivity and intrinsic sympathomimetic activity (ISA). Cardioselective agents predominantly block beta-1 receptors in the heart (for example, metoprolol, atenolol, bisoprolol). Nonselective agents block beta-1 and beta-2 receptors and can affect airways (for example, propranolol, nadolol). Some drugs also block alpha-1 receptors (carvedilol, labetalol) and may have ISA (pindolol) or non-ISA properties.

Indications include hypertension, angina pectoris, certain arrhythmias (such as atrial fibrillation and other supraventricular tachycardias), and heart failure with reduced ejection fraction (notably carvedilol, metoprolol succinate, and bisoprolol). They are used after myocardial infarction to reduce mortality, and for other conditions such as migraine prophylaxis and essential tremor.

Administration and pharmacokinetics vary: beta-blockers can be given orally or intravenously, with varying half-lives and degrees of hepatic metabolism. Lipophilic agents cross the blood-brain barrier more readily. Some are renally excreted. Caution is advised with abrupt withdrawal to avoid rebound tachycardia or ischemia.

Adverse effects include bradycardia, fatigue, dizziness, and hypotension. Nonselective agents may provoke bronchospasm in asthma or COPD. Sexual dysfunction can occur, and hypoglycemia symptoms may be masked. Contraindications include severe bradycardia, higher-grade AV block, and decompensated heart failure; use requires caution in asthma/COPD and diabetes. Interactions with calcium channel blockers and other heart-rate–lowering medications can enhance effects.