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What are beta bIockers and how do they work?
Beta blockers, also known as beta-adrenergic blocking agents, are drugs that block norepinephrine
and epinephrine (adrenaline) from binding to beta receptors on nerves. There are three types of beta
receptors and they control several functions based on their location in the body.
O Beta-1 (1) receptors are located in the heart, eye, and kidneys;
O beta (2) receptors are found in the lungs, gastrointestinal tract, liver,uterus, blood vessels,
and skeletal muscle; and
O beta (3) receptors are located in fat cells.
Beta blockers primarily block 1 and 2 receptors. By blocking the effect of norepinephrine and
epinephrine, beta blockers reduce heart rate; reduce blood pressure by dilating blood vessels; and
may constrict air passages by stimulating the muscles that surround the air passages to contract.
or what conditions are beta bIockers used?
Beta blockers are used for treating:
O abnormal heart rhythm,
O high blood pressure,
O heart failure,
O angina (chest pain),
O tremor,
O pheochromocytoma, and
O prevention of migraines.
They also have been found to prevent further heart attacks and death after a heart attack. Other
uses include the treatment of hyperthyroidism,akathisia (restlessness or inability to sit still),
and anxiety. Some beta blockers reduce the production of aqueous humor in the eye and therefore
are used for reducing pressure in the eye caused by glaucoma.
re there any differences between beta bIockers?
Beta blockers differ in the type of beta receptors they block and, therefore, their effects.
O Non-selective beta blockers, for example, propranolol (nderal), block 1 and 2 receptors and,
therefore, affect the heart, blood vessels, and air passages.
O Selective beta blockers, for example, metoprolol (Lopressor, Toprol XL) primarily block 1
receptors and, therefore, mostly affect the heart and do not affect air passages.
O Some beta blockers, for example, pindolol (Visken) have intrinsicsympathomimetic activity (SA),
which means they mimic the effects of epinephrine and norepinephrine and can cause an
increase in blood pressure and heart rate. Beta blockers with SA have smaller effects on heart
rate than agents that do not have SA.
O Labetalol (Normodyne, Trandate) and carvedilol (Coreg) block beta andalpha-1 receptors.
Blocking alpha receptors adds to the blood vessel dilating effect of labetalol (Normodyne,
Trandate) and carvedilol (Coreg).