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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.


something that blocks or obstructs a passage or activity; see also antagonist and blocking agent.
β-blocker (beta-blocker) beta-adrenergic blocking agent.
calcium channel blocker calcium channel blocking agent.
potassium channel blocker potassium channel blocking agent.
sodium channel blocker sodium channel blocking agent.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

β-ad·re·ner·gic block·ing a·gent

a class of drugs that competes with β-adrenergic agonists for available receptor sites; some compete for both β1 and β2 receptors (for example, propranolol) whereas others are primarily either β1 (for example, metoprolol) or β2 blockers; used in the treatment of a variety of cardiovascular diseases for which β-adrenergic blockade is desirable.
Farlex Partner Medical Dictionary © Farlex 2012


(bā′tə-blŏk′ər, bē′-)
A drug that blocks beta-receptors, thus counteracting the excitatory effects of norepinephrine and other beta-agonists released from sympathetic nerve endings. Beta-blockers are used primarily to treat angina, hypertension, arrhythmia, and migraine. Also called beta-adrenergic antagonist, beta-adrenergic blocker.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Any of a class of agents that blocks 1 and/or 2 adrenergic receptors in the nervous system, modulating cardiac functions, respiratory functions and the dilation of blood vessels.
Slowed heart rate, lowered blood pressure, reduced anxiety.
• General medicine
Angina, arrhythmias, hypertension, mitral valve prolapse, tachycardia, migraine, etc.
• Psychiatry
Aggression and violence, anxiety-related tremors and lithium-induced tremors, neuroleptic-induced akathisia, social phobias, panic states and alcohol withdrawal.

Carvedilol, sotalol, metoprolol, propranolol, atenolol, esmolol.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


A drug that blocks some of the effects of fight-or-flight hormone adrenaline (epinephrine and norepinephrine), slowing the heart rate and lowering the blood pressure.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


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.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
Beta-blockers are also important for the treatment of arrhythmias and coronary artery disease, in which they have been shown to improve survival and reduce the risk of future heart attacks and hospitalizations.
IOP at week 4 (IOP in TTFC group lower than IOP in beta-blocker group) if the true difference was >1.5 mmHg between treatments based on the assumption of a standard deviation (SD) of 3.5 mmHg and the use of a two-sample, one-sided t-test performed at a = 0.05 level of significance.
Patients who used beta-blockers had higher SBP and DBP and more acceptable MAP values than those who did not use beta-blockers.
The 2013 American College of Cardiology Foundation/American Heart Association heart failure guideline recommends the use of one of the 3 beta-blockers proven to reduce mortality (bisoprolol, carvedilol, or sustained-release metoprolol succinate) for all patients with current or previous symptoms of heart failure with reduced ejection fraction, unless contraindicated, to reduce morbidity and mortality.
Several recent meta-analyses have questioned the usefulness of beta-blockers as the primary tools to treat hypertension [1-3].
The rate of effective perioperative beta-blockade (the primary outcome) was assessed in the patients who met our definition of perioperative beta-blockade (at least one dose of beta-blocker administered anytime before or soon after induction of anaesthesia, as well as a prescription for beta-blocker for the duration of hospital admission).
Overall, the researchers found that adding beta-blockers as the second-line drug, in combination with thiazide diuretics or calcium channel blockers, caused an additional blood pressure reduction.
Evidence supports beta-blocker use in coronary artery disease and congestive heart failure.
For people who have type 2 diabetes and use beta-blockers, regular blood-sugar monitoring is especially important, because the drugs may mask the signs of low blood sugar (hypoglycemia), such as a rapid heartbeat.
PITTSBURGH -- Beta-blockers may have a protective effect in patients with traumatic brain injury, significantly reducing mortality, based on a retrospective study of more than 2,000 patients.
The use of cardioselective beta-blockers can improve survival in "carefully selected" patients with chronic obstructive pulmonary disease (COPD) undergoing vascular surgery, according to a report in the first October issue of the American Journal of Respiratory and Critical Care Medicine.