What are vasodilators, and how do they work (mechanism of action)?
A vasodilator is a drug that causes vasodilation, a widening (opening) of blood vessels that results from relaxation of the smooth muscle of the vessels. What widens in vasodilation actually is the diameter of the interior (lumen) of the vessel. The opposite of vasodilation is vasoconstriction.
This type of medicine works through several mechanisms. For example:
- ACE (angiotensin converting enzyme) inhibitors: ACE inhibitors slows (inhibits) the activity of the enzyme ACE, which decreases the production of a chemical (angiotensin) that causes the blood vessels to narrow. As a result, blood pressure reduces (lowers) because of the enlarged (dilated) blood vessels.
- ARBs (angiotensin receptor blockers): ARBs is another type of medicine that enlarges blood vessels. They work by blocking angiotensin from attaching to the smooth muscle of blood vessels. This causes vasodillation.
- CCBs (calcium channel blockers): The smooth muscles cells of the arteries use calcium for muscle contraction. CCBs block calcium from entering into the smooth cells, which relax the artery muscles. This leads to dilation (opening) of the artery.
- Nitrates: Nitrates are converted to nitric oxide, which activates another chemical that causes the veins and arteries to open. Doctors prescribe nitrates to treat angina (heart or cardiac pain).
This article does not contain the complete information about vasodilators. Please refer to the individual drug class or drug articles for further medical reference.
Why does a blood vessel dilate?
A blood vessel carries blood. They also help the body regulate blood pressure and blood flow to organs. When a blood vessel dilates (opens), it allows more blood flow.
Widening of arteries (a type of blood vessel) reduces blood pressure because dilation of the arteries makes it is easier for the heart to pump blood to the rest of the body.
- When arteries open, it increases the blood flow and oxygen supply to the heart.
- When veins open, it reduces the amount of blood returned to the heart chambers.
What diseases or other health conditions are vasodilators used to treat?
Doctors prescribe this type of medicine to treat several diseases and health conditions, and their symptoms. Some of the cardiovascular diseases and other health problems treated with these medications include:
- High blood pressure (hypertension)
- Congestive heart failure (CHF)
- Cardiac pain or heart pain (angina)
- Prevention of stroke
- Prevention of a heart attack
- Prevention of heart failure after a heart attack
- High blood pressure in pregnant women (Preeclampsia)
- High blood pressure in the lungs (pulmonary hypertension)
- Diabetic nephropathy
- Raynaud's syndrome
- Subarachnoid hemorrhage
Are there herbal, natural, or over-the-counter (OTC) vasodilator products available?
Examples of natural herbs or supplements that cause blood vessels to open include:
Is caffeine a vasodilator?
No. Caffeine is a vasoconstrictor. It is the opposite of a dilator, meaning that it causes blood vessels to constrict.
Vasodilator side effects and adverse effects
If you take this type of drug therapy for high blood pressure (hypertension) or another medical condition, it may reduce your blood pressure too much. If your blood pressure is too low (hypotension), you may feel dizzy, which is a symptom of low blood pressure.
Other side effects patients may experience include:
- Edema (fluid retention)
- Pulmonary edema
- Low blood glucose
- Abdominal pain
- Kidney failure
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Drug, Supplement, and Food interactions with vasodilators
Combining vasodilators may reduce blood pressure too much. However, in some patients, two or more vasodilators are combined to treat high blood pressure that cannot be controlled with only one antihypertensive medication. This is a list of examples of drug interactions that patients being treated with some types of vasodilators may experience.
Examples of ACE inhibitor interactions
- The use of potassium supplements, salt substitutes (which often contain potassium), or any medication that increase the body's potassium may result in excessive blood potassium levels because ACE inhibitors also increase blood levels of potassium.
- Angiotensin converting enzyme inhibitors also may increase the blood concentration of lithium (Eskalith, Lithobid) and lead to an increase in side effects from lithium. Symptoms of too much lithium include nausea, vomiting, cramping, and sometimes diarrhea.
- Combining ACE inhibitors with ARBs increases the risk of low blood pressure, high blood potassium, and kidney problems.
- Facial flushing, nausea, vomiting and low blood pressure (nitritoid reactions) may occur when injectable (gold sodium aurothiomalate [Myochrysine]), used in the treatment of patients with rheumatoid arthritis, is combined with ACE inhibitors.
Example of calcium channel blocker (CCBs) interactions
- Verapamil (Calan, Isoptin) and diltiazem (Cardizem) decrease the elimination of a number of medications that are broken down by the liver. Through this mechanism, verapamil and diltiazem may reduce the elimination and increase the blood levels of carbamazepine (Tegretol), simvastatin (Zocor), atorvastatin (Lipitor), and lovastatin (Mevacor). This can lead to toxicity from these medications.
- Grapefruit juice (approximately 200 ml) may increase blood concentrations of felodipine (Plendil), verapamil (Calan, Isoptin), nisoldipine (Sular), nifedipine (Adalat, Procardia), nicardipine (Cardene), and possibly amlodipine (Norvasc). Patients should not drink grapefruit juice within 2 hours before or 4 hours after taking of affected CCBs.
Examples of nitrate drug interactions
- Sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) increase the blood pressure lowering effects of nitrates and may cause excessive blood pressure reduction. Patients taking a medicine that is a nitrate should not take sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra).
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List of types and examples of generic and brand name vasodilators
List of ACE inhibitors
- benazepril (Lotensin)
- captopril (Capoten)
- enalapril (Vasotec, Epaned)
- fosinopril (Monopril)
- lisinopril (Prinivil, Zestril)
- moexipril (Univasc)
- perindopril (Aceon)
- quinapril (Accupril)
- ramipril (Altace)
- trandolapril (Mavik)
List of ARBs
- azilsartan (Edarbi)
- candesartan (Atacand)
- eprosartan (Teveten)
- irbesartan (Avapro)
- telmisartan (Micardis)
- valsartan (Diovan)
- losartan (Cozaar)
- olmesartan (Benicar)
List of CCBs
- amlodipine (Norvasc)
- clevidipine (Cleviprex)
- diltiazem (Cardizem)
- felodipine (Cardene, Cardene SR)
- nisoldipine (Sular)
- verapamil (Calan)
List of nitrates
- nitroglycerin (Gonitro, Nitrobid, Nitromist, Nitrolingual, Nitrostat, Nitrobid)
- isosorbide mononitrate (Ismo, Moneket)
- isosorbide dinitrate (Imdur, Isordil))
- Hydralazine (apresoline)
- Fenoldopam (carlopam)
- Nitroprusside (Nipride, Nitropress)
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What are pulmonary vasodilators?
Pulmonary vasodilators are medicines that dilate small arteries in the lungs. Doctors prescribe pulmonary vasodilators to treat patients with pulmonary arterial hypertension, a health condition that involves constriction of pulmonary arteries. Examples of pulmonary vasodilators include:
- Nitric oxide
- Nitroprusside (Nipride, Nitropress)
- Sildenafil (Revatio, Viagra)
- Tadalafil (Adcirca, Cialis)
- Bosentan (Tracleer)
Is it safe to use these drugs if I’m pregnant or breastfeeding?
- ACE inhibitors and ARBs: You should not take Ace inhibitors or ARBs if you are pregnant because they cause birth defects in the newborn. Doctor’s also do not recommend taking this type of drug if you are breastfeeding.
- CCBs: Researchers have not evaluated the safety of calcium channel in pregnant women.
- Verapamil crosses the placenta and affects the fetus. Verapamil and diltiazem are present in breast milk and doctors and other medical professionals do not recommend them for nursing mothers.
- Nitrates: Researchers have not adequately evaluated the safety of nitrates in pregnant or nursing women.
- Minoxidil and hydralazine: Researchers have not adequately evaluated the safety of these medicines in pregnant women. They are present in breast milk, and doctors and other health care professionals do not recommend in women who are breastfeeding.
What forms (preparations) are available for these drugs?
Vasodilators are available as tablets, capsules, and injections. Nitrates are available as sublingual tablets or spray, translingual spray, ointment, transdermal patches, and injectable solution.