beta-adrenergic blocking agent

beta-adrenergic blocking agent

n.

See beta-blocker.

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beta-adrenergic blocking agent.

See antiadrenergic.

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beta [ba´tah]

second letter of the Greek alphabet, β; used to denote the second position in a classification system. Often used in names of chemical compounds to distinguish one of two or more isomers or to indicate the position of substituent atoms or groups in certain compounds. Also used to distinguish types of radioactive decay; brain rhythms or waves; adrenergic receptors; secretory cells of the various organs of the body that stain with basic dyes, such as the beta cells of the pancreas; and the type of hemolytic streptococci that produce a zone of decolorization when grown on blood media.

beta-adrenergic blocking agent (beta-blocker) any of a group of drugs that block the action of epinephrine at beta-adrenergic receptors on cells of effector organs. There are two types of these receptors: β₁-receptors in the myocardium and β₂-receptors in the bronchial and vascular smooth muscles. The principal effects of beta-adrenergic stimulation are increased heart rate and contractility, vasodilation of the arterioles that supply the skeletal muscles, and relaxation of bronchial muscles.

Because of their effects on the heart, these agents are used to treat angina pectoris, hypertension, and cardiac arrhythmias. And, because they decrease the workload of the heart, they are effective in reducing the long-term risk of mortality and reinfarction after recovery from the acute phase of a myocardial infarction. They are an important adjunct in treatment of heart failure and are also used for prophylaxis of migraine.

Nonselective beta-adrenergic blocking agents affect both types of receptors and can produce bronchospasm in patients with asthma or chronic obstructive pulmonary disease. If such patients need one of these drugs, they should be given a cardioselective one that preferentially blocks the β₁-receptors in the heart.

Nonselective agents include propranolol (Inderal), used for treatment of angina, hypertension, arrhythmias, and migraine and for prophylaxis after the acute phase of a myocardial infarction; nadolol (Corgard), used for treatment of angina and hypertension; and timolol, used as an ophthalmic preparation (Timoptic) for treatment of glaucoma and as an oral preparation (Blocadren) for treatment of hypertension and for prophylaxis after the acute phase of a myocardial infarction. Cardioselective beta-adrenergic blocking agents are used for treatment of hypertension and include atenolol (Tenormin) and metoprolol (Lopressor).

beta particles negatively charged particles emitted by radioactive elements, the result of disintegration of neutrons; their source is the unstable atoms of radioactive metals such as radium and uranium. There are three general types of emissions from radioactive substances: alpha and beta particles and gamma rays. Beta particles are less penetrating than gamma rays and may be used to treat certain conditions on or near the surface of the body. See also radiation and radiation therapy.

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beta-blocker 

A drug that blocks or reduces the action of neurotransmitters on beta-adrenergic receptors. It reduces secretion of aqueous humour and consequently intraocular pressure and it is used in the treatment of glaucoma. Common beta-blockers include timolol maleate, betaxolol hydrochloride, carteolol hydrochloride, levobunolol hydrochloride and metipranolol. Timolol is often used together with another agent (combination drugs), e.g. timolol and brimonidine, timolol and dorzolamide, timolol and latanoprost. Syn. beta-adrenergic antagonist; beta-adrenergic blocking agent. See adrenergic receptors; miotics; sympatholytic drugs.