Beta Blockers
 |
Beta blockers, or beta-adrenergic blocking agents, are a class of drugs that reduce blood pressure by blocking the effects of the hormone epinephrine (adrenaline). These drugs have various indications, but are mainly used for the management of hypertension, cardiac arrhythmias, and cardio protection after myocardial infarction (heart attack).
General pharmacology
Beta receptors are proteins located on cells of different organs. These beta receptors can bind to epinephrine (adrenaline) and cause a metabolic change in the cell.
There are three known types of beta receptors: ß1-adrenergic receptors are located generally in the heart and kidney; ß2-adrenergic receptors are located mainly in the lungs, liver, uterus, gastrointestinal tract, vascular smooth muscles, and skeletal muscles; ß3-adrenergic receptors are located in fat cells.
Non-selective beta-blockers block ß1 and ß2-adrenergic receptors. But there are also cardio selective beta-blockers, meaning they block only ß1 receptors and others are selective to ß2 receptors. Selectivity can be lost at high drug doses.
When ß1 receptors are stimulated by epinephrine (adrenaline), there’s an increase of cardiac output, which means an increase of the heart rate and the volume of blood expelled with each beat. Beta-blockers prevent the binding of epinephrine to ß1 receptors, making the heart beat more slowly and with less force. This effect reduces the volume of blood expelled in blood vessels, which decreases blood pressure. Note that the heart has mainly ß1 receptors and some ß2 receptors.
When ß2 receptors are stimulated, smooth muscles around blood vessels relax. Beta-blockers therefore induce a small degree of contraction of blood vessels, which should usually increase blood pressure. But the effect is very mild and is countered by the reduced heart rate from the outcome of beta-blockers on the heart.
Examples of beta blockers
Examples of non-selective beta-blockers include:
- Alprenolol (Gubernal)
- Carteolol (Cartrol)
- Levobunolol (Liquifilm)
- Mepindolol (Betagon)
- Metipranolol (OptiPranolol)
- Nadolol (Corgard)
- Oxprenolol (Trasacor)
- Penbutolol (Levatol)
- Pindolol (Visken)
- Propranolol (Inderal LA)
- Sotalol (Betapace)
- Carvedilol (Coreg)
- Timolol (Blocadren)
Examples of ß1-Selective beta-blockers include:
- Acebutolol (Sectral)
- Atenolol (Tenormin)
- Betaxolol (Betoptic)
- Bisoprolol (Zebeta)
- Esmolol (Brevibloc)
- Metoprolol (Lopressor, Toprol XL)
- Nebivolol (Bystolic)
- Tilisolol (Selecal)
Therapeutic indications
Beta blockers aren't usually prescribed until other blood pressure medications, such as diuretics, haven't worked effectively. Doctors recommend beta blockers to treat certain conditions such as:
- High blood pressure.
- Irregular heart rhythm (arrhythmia).
- Heart failure.
- Chest pain (angina).
- Myocardial infarction (heart attacks).
- Glaucoma.
- Migraines.
- Generalized anxiety disorder.
- Hyperthyroidism.
- Certain types of tremors.
- Marfan syndrome.
- Depression.
Side effects
Most people who use beta blockers do not feel any adverse effects. But sometimes side effects occur with these drugs, which generally affect the heart.
Common side effects of beta blockers include:
- Fatigue.
- Cold hands.
- Dizziness.
- Weakness.
- Shortness of breath (less common).
- Trouble sleeping (less common).
- Loss of sex drive (less common).
- Depression (less common).
Cautions
Beta blockers are not usually prescribed to people suffering from asthma because the medication may trigger severe asthma attacks. In people who have diabetes, beta blockers may block signs of low blood sugar, such as rapid heart beat. It's therefore important to monitor blood sugar on a regular basis.
Beta blockers can also affect the cholesterol and triglyceride levels, causing a slight increase in triglycerides and a modest decrease in high-density lipoprotein (the "good" cholesterol). These changes generally are temporary. Taking beta blockers should not be abruptly stopped because doing so could increase the risk of a heart attack or other heart problems.
Major drug groups
Cardiovascular system
References
Sélection Reader's Digest, Le Guide canadien des médicaments, 2002.
Wikipedia, the free encyclopedia (www.wikipedia.org).
Mayo Clinic, medical information and tools for better living (www.mayoclinic.com).
CV Pharmacology, cardiovascular pharmacology concepts (www.cvpharmacology.com).
The information above should be used as a reference only. Any medical decision should not be done before consulting a health care professional.
Last update: 29th of July 2009.