Beta blockers Health Dictionary

Calcium-channel blockers inhibit the inward ?ow of calcium through the specialised slow channels of cardiac and arterial smooth-muscle cells. By thus relaxing the smooth muscle, they have important applications in the treatment of HYPERTENSION and ANGINA PECTORIS. Various types of calcium-channel blockers are available in the United Kingdom; these di?er in their sites of action, leading to notable di?erences in their therapeutic effects. All the drugs are rapidly and completely absorbed, but extensive ?rst-pass metabolism in the liver reduces bioavailability to around one-?fth. Their hypotensive e?ect is additive with that of beta blockers (see BETA-ADRENOCEPTOR-BLOCKING DRUGS); the two should, therefore, be used together with great caution – if at all. Calcium-channel blockers are particularly useful when beta blockers are contraindicated, for example in asthmatics. However, they should be prescribed for hypertension only when THIAZIDES and beta blockers have failed, are contraindicated or not tolerated.

Verapamil, the longest-available, is used to treat angina and hypertension. It is the only calcium-channel blocker e?ective against cardiac ARRHYTHMIA and it is the drug of choice in terminating supraventricular tachycardia. It may precipitate heart failure, and cause HYPOTENSION at high doses. Nifedipine and diltiazem act more on the vessels and less on the myocardium than verapamil; they have no antiarrhythmic activity. They are used in the prophylaxis and treatment of angina, and in hypertension. Nicardipine and similar drugs act mainly on the vessels, but are valuable in the treatment of hypertension and angina. Important di?erences exist between di?erent calcium-channel blockers so their use must be carefully assessed. They should not be stopped suddenty, as this may precipitate angina. (See also HEART, DISEASES OF.)... calcium-channel blockers

Also called adrenoceptor-blocking agents or alpha blockers, these drugs stop the stimulation of alpha-adrenergic receptors at the nerve endings of the SYMPATHETIC NERVOUS SYSTEM by HORMONES with ADRENALINE-like characteristics. The drugs dilate the arteries, causing a fall in blood pressure, so they are used to treat HYPERTENSION and also benign enlargement of the PROSTATE GLAND. Examples of this group of drugs are doxazosin, indoramin, phentolamine and prazosin. The drugs should be used with caution as some may cause a severe drop in blood pressure when ?rst taken.... alpha adrenergic blockers

See “Type II error”.... beta (i) error

See ADRENERGIC RECEPTORS.... beta adrenoceptor

Antibiotics with a beta-lactam ring in their molecular structure, including the penicillins and the cephalosporins. Act on penicillin binding proteins in the mucopeptides of the bacterial cell wall. Can be destroyed bybacterial beta-lactamases.... beta lactams

Linn. subsp. cicla (L.) Moq.

Synonym: B. vulgaris auct. non L.

Family: Chenopodiacae.

Habitat: Native to Mediterranean region; cultivated in North India, Maharashtra and South India.

English: Beet Root, Garden Beet, Chard.

Ayurvedic: Palanki.

Folk: Chukandar.

Action: Leaf—used in burns and bruises, also for diseases of spleen and liver. Tuber and seed— expectorant. Leaf and seed— diuretic. Leaf, tuber and seed— anti-inflammatory. Seed oil— analgesic.

Beet roots are eaten raw as salad or cooked. The leaves are nutritionally superior to roots and are a good source of vitamins and minerals.

The plant contains alkaloids ofwhich betaine is a mild diuretic and emme- nagogue.

In research, using rats, chard increased regeneration of beta cells in pancreas. Maximum reduction of blood glucose was after 42 days of administration. (J Ethnopharmacol, 2000, 73: 251-259.)

Beets are used orally as a supportive therapy in the treatment of liver diseases and fatty liver (possibly due to betaine). Ingestion of large quantities might worsen kidney disease. (Natural Medicines Comprehensive Database, 2007.)... beta vulgaris

see sympathomimetic.... beta agonist

see islets of Langerhans.... beta cells

one of a group of drugs that includes the *penicillins and the *cephalosporins. All have a four-membered beta-lactam ring as part of their molecular structure. Beta-lactam antibiotics function by interfering with the growth of the cell walls of multiplying bacteria. Bacteria become resistant to these antibiotics by producing beta-lactamases, enzymes (such as *penicillinase) that disrupt the beta-lactam ring. To counteract this, beta-lactamase inhibitors (e.g. *clavulanic acid) may be added to beta-lactam antibiotics. For example, co-amoxiclav is a mixture of *amoxicillin and clavulanic acid.... beta-lactam antibiotic

Also called beta blockers, these drugs interrupt the transmission of neuronal messages via the body’s adrenergic receptor sites. In the HEART these are called beta1 (cardioselective) receptors. Another type – beta2 (non-cardioselective) receptors – is sited in the airways, blood vessels, and organs such as the eye, liver and pancreas. Cardioselective beta blockers act primarily on beta1 receptors, whereas non-cardioselective drugs act on both varieties, beta1 and beta2. (The neurotransmissions interrupted at the beta-receptor sites through the body by the beta blockers are initiated in the ADRENAL GLANDS: this is why these drugs are sometimes described as beta-adrenergic-blocking agents.)

They work by blocking the stimulation of beta adrenergic receptors by the neurotransmitters adrenaline and noradrenaline, which are produced at the nerve endings of that part of the SYMPATHETIC NERVOUS SYSTEM – the autonomous (involuntary) network

– which facilitates the body’s reaction to anxiety, stress and exercise – the ‘fear and ?ight’ response.

Beta1 blockers reduce the frequency and force of the heartbeat; beta2 blockers prevent vasodilation (increase in the diameter of blood vessels), thus in?uencing the patient’s blood pressure. Beta1 blockers also affect blood pressure, but the mechanism of their action is unclear. They can reduce to normal an abnormally fast heart rate so the power of the heart can be concomitantly controlled: this reduces the oxygen requirements of the heart with an advantageous knock-on e?ect on the respiratory system. These are valuable therapeutic effects in patients with ANGINA or who have had a myocardial infarction (heart attack – see HEART, DISEASES OF), or who suffer from HYPERTENSION. Beta2 blockers reduce tremors in muscles elsewhere in the body which are a feature of anxiety or the result of thyrotoxicosis (an overactive thyroid gland – see under THYROID GLAND, DISEASES OF). Noncardioselective blockers also reduce the abnormal pressure caused by the increase in the ?uid in the eyeball that characterises GLAUCOMA.

Many beta-blocking drugs are now available; minor therapeutic di?erences between them may in?uence the choice of a drug for a particular patient. Among the common drugs are:

Primarily cardioselective	Non-cardioselective
Acebutolol	Labetalol
Atenolol	Nadolol
Betaxolol	Oxprenolol
Celiprolol	Propanolol
Metoprolol	Timolol

These powerful drugs have various side-effects and should be prescribed and monitored with care. In particular, people who suffer from asthma, bronchitis or other respiratory problems may develop breathing diffculties. Long-term treatment with beta blockers should not be suddenly stopped, as this may precipitate a severe recurrence of the patient’s symptoms – including, possibly, a sharp rise in blood pressure. Gradual withdrawal of medication should mitigate untoward effects.... beta-adrenoceptor-blocking drugs

Precursor of Vitamin A. Increases resistance against infection. Antioxidant. Together with Vitamins C and E form a vital line of defence in protection of strands of DNA, the genetic code, from cancerous mutation. Immune booster. Increases lymphocytes and T cells, part of the defence system.

Deficiency. Sun sensitivity; exposure inducing itching, burning and swelling of the skin. Kidney, bladder, and gut infections. Severe earache in young children. Strokes, heart attacks.

It is claimed that those who eat a diet rich in beta-carotene are less likely to develop certain types of cancer.

Smokers usually have low levels of beta-carotene in the blood. Statistics suggest that people who eat a lot of beta-carotene foods are less likely to develop lung, mouth or stomach cancer. In existing cases a slow-down of the disease is possible.

Daily dose. Up to 300mg. Excess may manifest as yellow discoloration of the skin, giving appearance of sun-tan.

Sources. Mature ripe carrots of good colour. A Finland study suggests that four small carrots contain sufficient beta-carotene to satisfy the recommended daily amount of Vitamin A. Orange and dark green fruits and vegetables. Broccoli, Brussels sprouts, spinach, pumpkin, apricots, peaches, oranges, tomatoes. Harvard Medical School study. Among 333 subjects with a history of heart disease, those who received beta-carotene supplements of 50 milligrams every other day suffered half as many heart attacks as those taking placebos. (Dr Charles Hennekens, Harvard Medical School) ... beta-carotene

A group of drugs, also known as beta-adrenergic blocking agents, prescribed principally to treat heart and circulatory disorders such as angina and hypertension. Beta-blockers block the effects of the sympathetic nervous system, which releases adrenaline (epinephrine) and noradrenaline (norepinephrine) at nerve endings that are known as beta receptors.

There are 2 types of beta receptor: beta 1 and beta 2. Beta 1 receptors are present in the heart and blood vessels, and beta 2 in the lungs. Some betablockers (such as acebutolol, atenolol, and metoprolol) are termed cardioselective and, because they act mostly on beta 1 receptors, are used mainly to treat heart disease such as angina, hypertension, and cardiac arrhythmia. The drugs are sometimes given after a myocardial infarction (heart attack) to reduce the likelihood of further damage to the heart muscle.

Other types of beta-blocker, such as oxprenolol, propranolol, and timolol, may be given to prevent migraine attacks by acting on blood vessels in the head; reduce the physical symptoms of anxiety; or control the symptoms of thyrotoxicosis. Beta-blocker drugs such as timolol are sometimes given in the

form of eye drops to treat glaucoma and work by lowering the fluid pressure in the eyeball.

Beta-blockers may reduce an individual’s capacity for strenuous exercise. The drugs may worsen the symptoms of asthma, bronchitis, or other forms of lung disease. They may also reduce the flow of blood to the limbs, causing cold hands and feet. In addition, sleep disturbance and depression can be side effects of beta-blockers.... beta-blocker drugs

(beta-adrenergic receptor blocker) a drug that prevents stimulation of the beta *adrenoceptors at the nerve endings of the sympathetic nervous system. Blockade of ?1 receptors causes a decrease in heart rate and force; blockade of ?2 receptors causes constriction of the airways and the arteries. Beta blockers include *acebutolol, *atenolol, *bisoprolol, *oxprenolol, *propranolol, and *sotalol; they are used to control abnormal heart rhythms, to treat angina, and to reduce high blood pressure (although they are no longer regarded by some experts as the first choice of drug for treating hypertension in the absence of heart disease, being less effective than newer antihypertensive drugs). Beta blockers that block both ?1 and ?2 receptor sites cause constriction of air passages in the lungs, and these drugs should not be used in patients with asthma and bronchospasm. Other beta blockers are relatively selective for the heart (cardioselective) and are less likely to constrict the airways. Some beta blockers (e.g. *carteolol, *levobunolol, and *timolol) reduce the production of aqueous humour and therefore the pressure inside the eye; they are taken as eye drops in the treatment of *glaucoma.... beta blocker