What Are Beta-Blockers? What Are Beta-Blockers For?

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Main Category: Heart Disease
Also Included In: Cardiovascular / Cardiology;  Hypertension
Article Date: 04 Dec 2009 - 0:00 PDT

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Beta-blockers, also known as beta-adrenergic blocking agents, beta-adrenergic antagonists, or beta antagonists, are a type of drug that block the action of the sympathetic nervous system of the heart, resulting in a relief of stress on the heart.

A beta-blocker blocks beta-adrenergic substances, for example adrenaline (apinephrine) in the involuntary nervous system (autononomic nervous system). Beta-blockers slow down the heart beat, reduce the force of the heart muscle's contractions, and decrease blood vessel contraction in the heart, brain, and the rest of the body.

Patients with cardiac arrhythmias (abnormal heart rhythms), tachycardias (accelerated heart rates), or irregular heart rhythms (atrial fibrillation), such as premature ventricular beats may be prescribed beta-blockers. They may also be useful in treating angina because they lower the heart muscle's demand for oxygen - angina pectoris occurs when the heart's demand for oxygen is greater than the supply.

Beta-blockers are useful in the treatment of high blood pressure (hypertension) because their effects on blood vessels lowers blood pressure. They are also key drugs in improving survival rates for patients after a heart attack.

Beta-blockers are also used for preventing migraine headaches and some familial or hereditary tremors.

In other words, beta-blockers are known as beta- adrenoreceptor blocking agents and are used to treat:

Commonly

• Angina
• Heart failure
• High blood pressure (hypertension)
• irregular heart beat (atrial fibrillation)
• Myocardial infarction (heart attack)
  
  Less commonly
• Prevention of migraine
• Thyrotoxicosis (overactive thyroid)
• Anxiety
• Tremor
• Glaucoma (as eye drops)

The first clinically useful beta adrenergic receptor antagonist was called Propranolol. It was invented by Sir James W. Black (born 1924), a Scottish doctor and pharmacologist. Sir James also synthesized Cimetidine (for the treatment of heartburn and peptic ulcers) and was awarded the Nobel Prize for Medicine in 1988. Propranolol revolutionized the medical management of angina pectoris - it is considered as one of the major contributions to clinical medicine and pharmacology of the 20th century.

According to Medilexicon's medical dictionary

A beta-adrenergic blocking agent is "a class of drugs that competes with β-adrenergic agonists for available receptor sites; some compete for both Beta₁ and Beta₂ receptors (propranolol) whereas others are primarily either Beta₁ (metoprolol) or Beta₂ blockers; used in the treatment of a variety of cardiovascular diseases for which beta-adrenergic blockade is desirable."

Types of beta-blockers

There are various types of beta-blockers (beta-adrenoceptor blocking agents). Which one a patient has depends on his/her condition.

Below are some examples:

Acebutolol (Sectral)
Atenolol (Tenormin)
Betaxolol (Betoptic)
Bisoprolol (Cardicor, Emcor, Zebeta)
Carteolol (Teoptic)
Carvedilol (Coreg, Eucardic)
Celiprolol (Celectol)
Labetalol (Trandate)
Levobunolol (Betagan)
Metipranolol (Metipranolol Minims)
Metoprolol (Betaloc, Lopresor, Lopressor, Toprol XL)
Nadolol (Corgard)
Nebivolol (Bystolic, Nebilet)
Oxprenolol (Trasicor)
Pindolol (Visken)
Propranolol (Inderal LA)
Sotalol (Beta-Cardone, Sotacor)
Timolol (Betim, Nyogel, Timoptol)

What do beta-blockers do?

Beta-blockers block the release of noradrenalin in parts of the body. Noradrenalin is released by the nerves when they are stimulated - it is a chemical that conveys messages to other parts of the body, including muscles, blood vessels and the heart.

• Heart problems - for a patient with heart problems beta-blockers can reduce the workload for the heart; so that it does not have to work so hard to supply all parts of the body with oxygen-rich blood. For people with angina, heart failure, or after a heart attack, reducing the heart's workload is crucial.
  
  Beta-blockers can also block the stimulation of the heart form electrical impulses - they can control irregular heartbeats - thus lowering the activity of the heart and slowing down the heart rate.


• Hypertension - beta-blockers lower blood pressure by slowing down the heart rate, as well as reducing the force of the heart. Blood still gets to all parts of the body, but at reduced pressure.


• Glaucoma - pressure within the eyeball is reduced with beta-blocker eye drops. The medication lowers the production of fluid inside the eye ball (aqueous humor).

Things to bear in mind with beta-blockers

The following people should not take beta-blockers:

• Patients with a history of asthma (unless the doctor says so)
• Patients with a history of bronchospasm (unless the doctor says so)
• Patients with second or third degree heart block
• Patients with severe peripheral arterial disease (including Raynaud's syndrome)
• Patients with worsening, unstable heart failure (can be used for stable heart failure)

For the following people, beta-blockers should be used with caution:

• Patients with diabetes, especially those with regular episodes of low blood sugar (hypoglycemia)
• Patients with MG (myasthenia gravis)
• Patients with a slow heart rate (bradycardia)
• Patients with low blood pressure (hypotension)
• Patients with hypertension that results from an adrenal gland tumor (pheochromocytoma)
• Patients with high blood acid levels (metabolic acidosis)
• Patients with Prinzmetal angina

Pregnancy and breastfeeding - in some cases certain types of beta-blockers may be used.

Getting off beta-blockers - Patients must not stop taking beta-blockers suddenly without their doctor's advice and close supervision. Suddenly ceasing beta-blocker treatment may exacerbate the patient's condition, especially after a heart attack or for the treatment of angina.

What are the side effects of beta-blockers?

The most common side effects are:

• Cold feet
• Cold hands
• Diarrhea
• Fatigue
• Nausea
• Very slow heartbeat

The following less common side effects are also possible:

• Sleeping difficulties and disturbances
• Bad dreams (nightmares)
• Erectile dysfunction (male inability to achieve or sustain an erection during sex)

Driving - some patients may experience dizziness or fatigue; in such cases they should not drive. However, this is rare.

Beta-blocker interactions with other drugs

Drug interaction is the extra effects two different medicines can have on the body when taken together - effects beyond their primary purposes. Beta-blockers can interact with the following medications:

• Antipsychotics - these medications are commonly prescribed for patients with bipolar disorder or schizophrenia. When taken with some beta-blockers the risk of arrhythmias is greater.


• Clonidine - a medication prescribed for either patients with hypertension (high blood pressure) or migraines. A patient who is taking both clonidine and beta-blockers and then suddenly stops taking clonidine has a greater risk of experiencing a sudden and sharp rise in blood pressure (rebound hypertension).


• Digoxin - prescribed for patients with congestive heart failure and certain cardiac arrhythmias. When taken with beta-blockers there is a higher risk of slow heart rate (bradycardia).


• Diltiazem - a medication that dilates blood vessels, prescribed for patients with angina pectoris or hypertension. When taken with beta-blockers there is a higher risk of slow heart rate (bradycardia).


• Drugs to control high blood pressure (antihypertensives) - when taken with beta-blockers the patient may experience hypotension (a serious drop in blood pressure).


• Drugs to control irregular heartbeats (anti-arrhythmics) - when taken with beta-blockers the risk of impaired function of the heart (myocardial depression) is greater, as is the risk of irregular heartbeats (arrhythmias).


• Mefloquine - a drug for the treatment of malaria resistant to chloroquine phosphate. When taken with beta-blockers the result may be bradycardia.


• Nifedipine - this drug reduces calcium ions available to heart and smooth muscle, used in the treatment of angina pectoris. When taken with beta-blockers there is a higher risk of hypotension (low blood pressure).


• Nisoldipine - a calcium channel blocker used in the treatment of high blood pressure (hypertension). When taken with beta-blockers there is a higher risk of hypotension (low blood pressure).


• Verapamil - used in the treatment of hypertension, angina pectoris, and certain cardiac arrhythmias. When taken with beta-blockers there is a higher risk of hypotension (low blood pressure).

Check with your pharmacist or doctor for a more comprehensive and up-to-date list of beta-blocker interactions.

Written by Christian Nordqvist


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