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Vasodilators are medicines that act directly on muscles in blood vessel walls to make blood vessels widen (dilate).
Vasodilators are used to treat high blood pressure (hypertension). By widening the arteries, these drugs allow blood to flow through more easily, reducing blood pressure. Controlling high blood pressure is important because the condition puts a burden on the heart and the arteries, which can lead to permanent damage over time. If untreated, high blood pressure increases the risk of heart attack, heart failure, stroke, or kidney failure. Vasodilators usually are prescribed with other types of blood pressure drugs and rarely are used alone.
Examples of vasodilators are hydralazine (Apresoline) and minoxidil (Loniten). The vasodilator hydralazine also may be used to control high blood pressure in pregnant women or to bring down extremely high blood pressure in emergency situations. In the forms used for treating high blood pressure (tablets or injections), these drugs are available only with a physician's prescription. A liquid form of minoxidil, used to promote hair growth in people with certain kinds of baldness and is applied directly to the scalp, and is sold without a prescription.
The recommended dosage depends on the type of vasodilator. The physician who prescribed the drug or the pharmacist who filled the prescription can recommend the correct dosage. This medicine should only be used as directed.
Physicians usually prescribe vasodilators along with other blood pressure medicines. Taking each drug at the correct time is extremely important. Health care providers can offer suggestions on how to remember when to take each drug.
Seeing a physician regularly while taking a vasodilator is important, especially during the first few months. The physician will check to make sure the medicine is working as it should and will watch for unwanted side effects. People who have high blood pressure often feel fine. But even when they feel well, patients should keep seeing their physicians and taking their medicine.
Vasodilators will not cure high blood pressure, but will help control the condition. To avoid the serious health problems that high blood pressure can cause, patients may have to take medicine for the rest of their lives. Furthermore, medicine alone may not be enough. People with high blood pressure also may need to avoid certain foods and keep their weight under control. The health care professional who is treating the condition can offer advice on what measures may be necessary.
Some people feel dizzy or have headaches while using this medicine. These problems are especially likely to occur in older people, who are more sensitive than younger people to the medicine's effects. Anyone who takes these drugs should not drive, use machines, or do anything else that might be dangerous until they know how the drugs affect them.
People who have certain medical conditions or who are taking certain other medicines may have problems if they take vasodilators. In the past, patients with severe aortic stenosis could not use vasodilators because they could cause blood pressure to drop too low and result in severe complications. However, in 2003, a report announced that the vasodilator nitroprusside was safe in these patients and rapidly improved their cardiac function. Before a patient takes vasodilators, he or she should be sure to let the physician know about any of these conditions:
ALLERGIES. Anyone who has had an unusual reaction to a vasodilator in the past should let his or her physician know before taking this type of drug again. The physician also should be told about any allergies to foods, dyes, preservatives, or other substances.
PREGNANCY. Several problems—from excess hair growth to blood abnormalities—have been reported in babies whose mothers take certain vasodilators during pregnancy. In studies of laboratory animals, hydralazine caused birth defects in mice and rabbits, but not in rats. The effects of taking vasodilators during pregnancy have not been specifically studied in humans. Women who are pregnant or who may become pregnant should check with their physicians before using this medicine. Women who become pregnant while taking a vasodilator should tell their physicians right away.
BREASTFEEDING. Women who are breastfeeding their babies or who plan to breastfeed should check with their physicians before using this medicine.
OTHER MEDICAL CONDITIONS. Using a vasodilator to lower blood pressure may worsen the problems that result from heart disease, blood vessel disease, or a recent heart attack or stroke. This medicine also may make angina (chest pain) worse. Vasodilators may make pheochromocytomas (tumors of the adrenal medulla), more active. Before using a vasodilator, people with any of these medical problems should make sure their physicians are aware of their conditions.
People with kidney disease also should check with their physicians before using a vasodilator. Side effects may be greater in these people because their kidneys are slow to clear the medicine from the body.
USE OF CERTAIN MEDICINES. Taking vasodilators with certain other drugs may affect the way the drugs work or may increase the chance of side effects. Any other prescription or nonprescription (over-the-counter) medicine should not be taken along with a vasodilator unless it has been discussed with the physician who prescribed the vasodilator.
Some side effects of vasodilators go away as the body adjusts to the drug and do not need medical attention unless they continue or interfere with normal activities. These include:
- nausea or vomiting
- loss of appetite
In addition, minoxidil may cause a temporary increase in hair growth, especially on the face, arms, and back. Patients who are bothered by this should check with their physicians.
Other side effects of vasodilators should have medical attention. Rapid or irregular heartbeat are reasons to check with a physician immediately. And if any of the following problems occur, a physician should be consulted as soon as possible:
Additional side effects are possible. Anyone who has unusual symptoms while taking a vasodilator should get in touch with his or her physician.
Vasodilators may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the chance of side effects may be greater. In addition, many prescription and nonprescription (over-the-counter) drugs may affect blood pressure. No other medication should be taken without the approval of the physician who prescribed the vasodilator. In particular, avoiding over-the-counter medicines for appetite control, colds, cough, sinus problems, asthma, hay fever and other allergies, should be avoided as these may increase blood pressure. At the other extreme, dangerously low blood pressure may result when drugs such as the blood pressure medicine guanethidine (Ismelin) or nitrates, used to treat chest pain, are combined with vasodilators.
Adrenal gland — One of a pair of organs located next to the kidneys. The adrenal glands produce hormones that control many body functions.
Adrenal medulla — The inner part of the adrenal gland. The adrenal medulla produces the hormones epinephrine (adrenaline), which stimulates the heart, tightens blood vessels, and relaxes some smooth muscles; and norepinephrine, which has similar effects.
Arteries — Blood vessels that carry blood away from the heart to the cells, tissues, and organs of the body.
Moon, Mary Ann. "Vasodilators Can Help, Not Hurt." Internal Medicine News June 1, 2003: 40-41.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.