Beta blockers are medications that are used for a variety of conditions. One use for these drugs is to treat angina pectoris---chest pain that is caused by a decreased supply of oxygen to the heart. Beta blockers, as the name suggests, work by blocking cell receptors called beta receptors. Several types of beta blockers may be used in the treatment of angina.
Propanalol
According to the medical reference UpToDate, propranalol was the first medication to be used clinically as a treatment for angina. It is known as a nonselective beta blocker because it blocks both types of beta receptors: beta-1 and beta-2. Beta-1 receptors are found mainly in the heart; beta-2 receptors are found in the heart but mainly in the airway muscles and the blood vessels of the body. Blocking the beta-1 receptors decreases the amount of oxygen the heart needs in several ways; this results in an improvement in angina symptoms. However, when the beta-2 receptors are blocked, the airways may not be able to dilate properly; similarly, blocking, or inhibiting, the beta-2 receptors of the blood vessels will interfere with their ability to dilate correctly. Side effects of propranolol include fainting, decreased blood pressure, and chest pain, along with a variety of neurological side effects such as amnesia or catatonia. Skin-related side effects include hair loss, and rashes. Nausea, vomiting, and diarrhea may also occur. The list of potential side effects is a long one; fortunately, as the pharmacology database MicroMedex indicates, these are all extremely rare, often being reported as case reports of individuals or very small groups of people experiencing a certain effect.
Atenolol
Atenolol is considered a "cardioselective" beta blocker, indicating that the medication mainly inhibits the beta-1 receptors without interfering with the beta-2 receptors. This means that the ability of the blood vessels throughout the body, as well as the ability of the bronchial, or airway muscles to dilate correctly, are minimally affected. Studies looking at the effectiveness of this medication are over 30 years old, but are conclusive in their findings that this medication is as effective as propranolol in decreasing the number of episodes of chest pain patients experience. Atenolol has also been found to increase the ability of people with angina to exercise without pain.
According to UpToDate, important side effects that may occur with atenolol include a constant, decreased heart rate; swelling of the hands and feet---known as edema; heart failure; abnormal heart rhythms; or, ironically, chest pain. Dizziness, fatigue or insomnia, erectile dysfunction, diarrhea or constipation are also quite common, occurring in up to 10 percent of patients taking atenolol.
Pindolol
Pindolol is an example of a beta blocker that also has the ability to "rev up" the part of the nervous system known as the sympathetic nervous system. This is a potential advantage because when the beta-1 receptors of the heart are blocked, one result is a decrease in heart rate. A heart rate that is too slow can be dangerous, so a medication that can treat the angina without causing as much of a decline in the heart's ability to function is a potential benefit. However, UpToDate contributors Joseph Kannam, M.D., Julian Aroesty, M.D., and Bernard Gersh, M.B., Ch.B., point out that this potential benefit does not always occur, and report that as a result, this medication is only used for angina in specific cases. For instance, if a person tends to have a low heart rate while resting while not on medication, his physician may use pindolol to treat angina in the hopes that the patient's heart rate will not decrease further. MicroMedex reports that side effects of pindolol include edema as well as joint or muscle pain. Fatigue and dizziness are also quite common.
Carvedilol
Carvedilol is an example of a beta blocker that is nonselective--it blocks both beta-1 and beta-2 receptors--but also blocks another type of receptor called the alpha-1 receptor. This results in blood vessel dilation, instead of the potential constriction of blood vessels seen with other nonselective medications such as propranolol. A study of over 100 patients, published in 1998 in the American Journal of Cardiology, found that patients who took carvedilol experienced longer periods of time without angina symptoms and tolerated the medication well. According to MicroMedex, possible side effects include decreased heart rate, weight gain, diarrhea, dizziness, and fatigue. More severe side effects are rare and include blood cell abnormalities, asthma, and a life-threatening skin condition called Stevens-Johnson syndrome.
References
- "American Journal of Cardiology"; Effectiveness of three different doses of carvedilol for exertional angina. Carvedilol-Angina Study Group.; R. Weiss et. al.; October 1998
- "UpToDate"; Denise S. Basow; 2010
- MicroMedex: Carvedilol, Propranolol, Pindolol
