How Vasodilator Drugs Work

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Introduction to How Vasodilator Drugs Work

High blood pressure is a growing public health problem not only in the United States, but worldwide. Among the people in the United States who have high blood pressure, only 37 percent have the condition under control.

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Among the people in the United States who have high blood pressure, only 37 percent have the condition under control.

Vasodilator drugs are medications that get their name from the Latin words "vasa," which means "vessel," and "dilate," which means "to make wider." These drugs work by relaxing the smooth muscles that line the walls of blood vessels -- causing the blood vessels to increase in diameter and allow blood to flow through more easily. As a result, the heart doesn't need to work as hard to pump blood through them, and blood pressure is lowered because there's less force in the vessels. Vasodilators aren't a cure for high blood pressure; however, they can help control the condition.

Doctors prescribe vasodilators for the treatment of high blood pressure and angina (chest pain caused by heart disease). Vasodilators can also relieve symptoms associated with heart failure, a condition in which the heart cannot pump enough blood to nourish the cells throughout the body.

High blood pressure is dangerous because it puts stress on the heart and the blood vessels, which, over time, can lead to permanent damage. If untreated, high blood pressure increases a person's risk of having a heart attack or stroke, or developing heart failure or kidney failure.

There are several classifications of vasodilator drugs. Arterial dilators primarily affect arteries, venous dilators work on veins and mixed dilators have an effect on both arteries and veins. Most vasodilator drugs fall into the last category.

Doctors prescribe arterial dilators for high blood pressure and heart failure, but not for angina. Venous dilators are very effective for angina and are sometimes used for heart failure, but they're not used as primary treatment for high blood pressure.

We'll learn more about types of vasodilators on the next page.

Types of Vasodilator Drugs

It's more common to classify vasodilator drugs based on the way they work to widen blood vessels. Some act directly on blood vessels, making them relax and become wider. Others inhibit specific actions of the body that would cause the blood vessels to tighten and become narrower.

ACE inhibitors (angiotensin-converting enzyme inhibitors) work by blocking the body's production of a chemical called angiotensin II. This chemical causes blood vessels to narrow -- so, blocking its production allows blood vessels to become wider. As a result, more blood can flow into the vessels, and the heart's workload is decreased. For heart failure patients, doctors prescribe ACE inhibitors more often than any other type of vasodilator. In patients with chronic heart failure, ACE inhibitors not only help relieve symptoms but also slow disease progression and increase life span. ACE inhibitors also increase blood flow to the kidneys, which helps the kidneys excrete more sodium and water and helps reduce fluid overload, a common symptom of heart failure.
Angiotensin II receptor blockers achieve the same effect as ACE inhibitors, but they work in a different way. Instead of preventing the production of angiotensin II, they block it from being able to act in the muscles that line the blood vessels. So they indirectly decrease the heart's workload.
Alpha blockers reduce the workload of the heart by blocking certain chemicals from acting.

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This plate of food would definitely not be a part of a
heart-healthy diet to lower blood pressure.

Calcium channel blockers reduce the workload of the heart by blocking signals that tell blood vessels in the heart to tighten They have a direct slowing effect on the heart muscle.
Nitrates work by dilating the veins of the body and by working directly on the muscles of the heart's blood vessels, causing them to relax and increasing the flow of oxygen-rich blood to the heart.
Thiazide diuretics are one of four types of diuretic drugs. These medications increase the kidney's production of urine, thus removing fluid and minerals (including sodium) from the body. Low-dose thiazide diuretics also work as vasodilators.
Central adrenergic inhibitors interfere with signals from the brain that tell blood vessels to tighten. This class of vasodilator drugs is also used for other conditions, including panic attacks and migraine headaches.

Many vasodilator drugs have other effects that can sometimes provide additional benefits. For example, some calcium channel blockers not only dilate blood vessels but also lessen the heart's mechanical and electrical functions, which in turn can enhance their blood-pressure-lowering action and may also help regulate arrhythmias (irregular heart rhythms).

Doctors decide which type of vasodilator drug to prescribe based on medical history, current symptoms and other medical conditions. Vasodilator drugs are rarely used alone -- they're usually prescribed in combination with other types of blood pressure drugs.

Once people who have high blood pressure begin taking vasodilator drugs, they generally need to keep taking them for the rest of their lives. Without these medicines, they would be at risk of developing serious health problems. And medicine alone may not be enough. People who are taking vasodilator drugs are usually encouraged by their doctors to make healthy lifestyle changes, like eating a heart-healthy diet, getting regular exercise and practicing stress-management techniques.

Side Effects of Vasodilator Drugs

Some of the side effects of vasodilator drugs are just temporary. The following side effects usually pass after the person's body gets used to the medicine.

Loss of appetite
Headache
Diarrhea
Nausea or vomiting

Other side effects call for medical attention. If any of the following side effects occurs, a patient should check with his or her doctor.

Abnormal heart rhythm
Pounding heartbeat
Dizziness or lightheadedness
Sneezing, respiratory congestion, itching, skin rashes or other allergic reactions)
Low blood pressure
Shallow, dry cough
Fainting
Weight gain
Fluid retention
Sleepiness or weakness
Abnormal sensitivity to sunlight, resulting in severe sunburn or rash
Pain in joints or back
Unusual bleeding (like nosebleeds)
Unusual changes in appearance of skin (rash, change in coloration)

In general, older people tend to be more sensitive to the side effects (especially dizziness and lightheadedness) of vasodilators.

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If you're taking vasodilator drugs, you shouldn't drink grapefruit juice.

Patients who are taking vasodilators shouldn't take any other medicines (either prescription or over-the-counter) or dietary supplements (including herbal remedies) without first talking with their doctor. The following substances may intensify the effects of vasodilators and lead to severe low blood pressure:

Other vasodilators, unless prescribed as part of a combination therapy
Alcohol, which is itself a vasodilator
Medications for sexual dysfunction
Nicotinic acid, a form of vitamin B3 that is sometimes used as a cholesterol-reducing drug
Grapefruit juice, which interferes with the liver's ability to rid the body of vasodilators and many other substances. This could lead to a buildup of vasodilators to dangerous levels in the body.

Substances that can counteract the effects of some vasodilators and increase blood pressure include:

Aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs)
Nicotine
Narcotics (prescription-strength painkillers)

In addition, some over-the-counter medications for cough, colds, flu, sinus problems, hay fever, and asthma, as well as those for bloodshot (red) eyes or appetite control, may adversely react with vasodilators.

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How Vasodilator Drugs Work