Beta-adrenergic blocking agents

Beta-adrenergic blocking agents are a class of medicines that bind to beta-adrenoreceptors and prevent the binding of norepinephrine and epinephrine at these receptors. This prevents sympathetic stimulation of the heart and reduces heart rate, cardiac contractility, conduction velocity, and relaxation rate which decreases myocardial oxygen demand and increases exercise tolerance. Beta-adrenergic blocking agents are commonly referred to as beta-blockers.

Beta-blockers can be grouped into those that are non-selective (block both beta-1 and beta-2 receptors, such as nadolol, penbutolol, pindolol, propranolol, sotalol, and timolol), and those that are cardioselective (only block beta-1 receptors, and include acebutolol, betaxolol, bisoprolol, esmolol, and metoprolol). Some, like atenolol, are only cardioselective at low dosages.

Beta-1 and beta-2 receptors are both found in the heart, although beta-1 receptors are the predominant type. Beta-2 receptors are found in vascular smooth muscle such as in the blood vessels and the muscle lining the airways. Some beta-blockers (for example acebutolol, carteolol, labetalol, penbutolol, pindolol) are called partial agonists and possess intrinsic sympathomimetic activity (ISA) because they partially activate the beta-receptor while preventing norepinephrine from binding to the receptor. Others (such as betaxolol, metoprolol, pindolol, and propranolol) have membrane stabilizing activity. Carvedilol and labetalol block alpha-1 adrenergic receptors in addition to beta receptors, which lowers blood pressure and further vasodilates the arteries.

Beta-adrenergic blocking agents are used to treat angina, control abnormal heart rhythms and to reduce high blood pressure. They may be used following a myocardial infarction (heart attack) to improve survival rates. Blocking of beta-receptors, especially by nonselective beta-blockers, may cause bronchial constriction (narrowing of the airways). People with pre-existing respiratory conditions are more at risk.