Beta-blockers, also known as beta antagonists, beta-adrenergic blocking agents, or beta-adrenergic antagonists, are drugs that are prescribed to treat several different types of conditions, including hypertension (high blood pressure), angina, some abnormal heart rhythms, heart attack (myocardial infarction), anxiety, migraine, glaucoma, and overactive thyroid symptoms.
Beta-blockers block the action of the sympathetic nervous system of the heart, thus reducing stress on the heart. The sympathetic nervous system activates the "fight or flight" response. It is part of the autonomic nervous system.
Beta-blockers block beta-adrenergic substances, such as apinephrine (adrenaline) in the autonomic nervous system (involuntary nervous system). They slow down the heart beat, decrease the force of the contractions of the heart muscles, and reduce blood vessel contraction in the heart, brain, as well as the rest of the body.
Doctors may prescribe beta-blockers for patients with tachycardias (rapid heart rates). They help patients with angina by lowering the amount of oxygen the heart muscles require. Angina pectoris occurs when the heart requires more oxygen than it is getting.
Beta-blockers can help hypertensive patients because their effects on blood vessels lower blood pressure.
Patients with hereditary tremors as well as those who suffer from migraines may benefit from taking beta-blockers.
In other words, beta-blockers are known as beta-adrenoreceptor blocking agents and are used to treat the following:
- Heart failure
- High blood pressure (hypertension)
- Irregular heart beat (atrial fibrillation)
- Myocardial infarction (heart attack)
- Prevention of migraine
- Thyrotoxicosis (overactive thyroid)
- 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.
Types of beta-blockers
There are various types of beta-blockers (beta-adrenoceptor blocking agents). Which one a patient is prescribed will depend on his/her condition.
Common types of beta-blockers:
Atenolol (Tenormin) is a common type of beta-blocker.
- 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.
On the next page we look at the side effects of beta-blockers and the possible interactions of beta-blockers with other drugs.