Type of Surgery
Last updated: 01/28/2009
Diuretics are medicines that help reduce the amount of water in the body.
Diuretics are used to treat the buildup of excess fluid in the body that occurs with some medical conditions such as congestive heart failure, liver disease, and kidney disease. Some diuretics are also prescribed to treat high blood pressure. Most of these drugs act on the kidneys to increase urine output. This reduces the amount of fluid in the bloodstream, which in turn lowers blood pressure.
Diuretics may be used in surgery to reduce blood pressure and swelling. Mannitol, an osmotic diuretic, may be used to reduce swelling in the brain, which may be necessary for some neurosurgical procedures.
There are several types of diuretics, also called water pills:
- Loop diuretics, such as bumetanide (Bumex) and furosemide (Lasix), get their name from the loop-shaped part of the kidneys where they have their effect.
- Thiazide diuretics include such commonly used diuretics as hydrochlorothiazide (HydroDIURIL, Esidrix), chlorothiazide (Diuril), and chlorthalidone (Hygroton).
- Potassium-sparing diuretics prevent the loss of potassium, which is a problem with other types of diuretics; examples of potassium-sparing diuretics are amiloride (Midamor) and triamterene (Dyrenium).
- Osmotic diuretics keep water from being reabsorbed in the kidney. Mannitol, which is given by intravenous drip, is commonly used to reduce cerebral edema (swelling of the brain).
- Carbonic anhydrase inhibitors are another form of diuretic. While they cause water loss through the kidneys by changing the acidity of urine, their most common use is in treatment of glaucoma, an eye disease caused by increased pressure inside the eyeball. Acetazolamide (Diamox) is the most commonly used carbonix anhydrase inhibitor. Acetazolamide is given by mouth, but other drugs may be given as eye drops.
In addition, some medicines contain combinations of two diuretics. The brands Dyazide and Maxzide, for example, contain the thiazide diuretic hydrochlorothiazide with the potassium-sparing diuretic triamterene.
Some nonprescription (over-the-counter) medicines contain diuretics. However, the medicines described here cannot be bought without a physician's prescription. They are available in tablet, capsule, liquid, and injectable forms.
Warnings and cautions apply to the thiazide and loop diuretics, which are given by mouth over a long period of time. They do not apply to a single dose of an osmotic diuretic, which may be given immediately before or during surgery.
The recommended dosage depends on the type of diuretic and may be different for different patients, but they should check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage, and take the medicine exactly as directed.
Seeing a physician regularly while taking a diuretic is important. The physician will check to make sure the medicine is working as it should and will watch for unwanted side effects.
Some people feel unusually tired when they first start taking diuretics. This effect usually becomes less noticeable over time, as the body adjusts to the medicine.
Because diuretics increase urine output, people who take this medicine may need to urinate more often, even during the night. Health care professionals can help patients schedule their doses to avoid interfering with their sleep or regular activities.
For patients taking the kinds of diuretics that rob potassium from the body, physicians may recommend adding potassium-rich foods or drinks such as citrus fruits and juices to the diet. Or, they may suggest taking a potassium supplement or taking another medicine that keeps the body from losing too much potassium. If the physician recommends any of these measures, the patient must make sure to closely follow the directions. The patient should not make other diet changes without checking with the physician. People who are taking potassium-sparing diuretics should not add potassium to their diets, as too much potassium may be harmful.
People who take diuretics may lose too much water or potassium when they get sick, especially if they have severe vomiting and diarrhea. They should check with their physicians if they become ill.
These medicines make some people feel lightheaded, dizzy, or faint when they get up after sitting or lying down. Older people are especially likely to have this problem. Drinking alcohol, exercising, standing for long periods, or being outdoors in hot weather may make the problem worse. To lessen the problem, a person should get up gradually and hold onto something for support if possible. The patient should avoid drinking too much alcohol and be careful in hot weather or when exercising or standing for a long time.
Anyone who is taking a diuretic should be sure to tell the health care professional in charge before having surgical or dental procedures, medical tests, or emergency treatment.
Some diuretics make the skin more sensitive to sunlight. Even brief exposure to sun can cause severe sunburn, itching, a rash, redness, or other changes in skin color. While being treated with this medicine, the person should avoid being in direct sunlight, especially between 10 A.M. and 3 P.M.; wear a hat and tightly woven clothing that covers the arms and legs; use a sunscreen with a skin protection factor (SPF) of at least 15; protect the lips with a sun-block lipstick; and not use tanning beds, tanning booths, or sunlamps. People with fair skin may need to use a sunscreen with a higher skin protection factor.
People who have certain medical conditions or who are taking certain other medicines may have problems if they take diuretics. Before taking these drugs, they should be sure to let the physician know about any of these conditions.
ALLERGIES. Anyone who has had unusual reactions to diuretics or sulfonamides (sulfa drugs) in the past should let the physician know. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.
PREGNANCY. Diuretics will not help the swelling of hands and feet that some women experience during pregnancy. In general, pregnant women should not use diuretics unless a physician recommends their use. Although studies have not been done on pregnant women, studies of laboratory animals show that some diuretics can cause harmful effects when taken during pregnancy.
BREASTFEEDING. Some diuretics pass into breast milk, but no reports exist of problems in nursing babies whose mothers use this medicine. However, thiazide diuretics may decrease the flow of breast milk. Women who are breastfeeding and need to use a diuretic should check with the physician.
OTHER MEDICAL CONDITIONS. Side effects of some diuretics may be more likely in people who have had a recent heart attack or who have liver disease or severe kidney disease. Other types of diuretics may not work properly in people with liver disease or severe kidney disease. Diuretics may worsen certain medical conditions such as gout, kidney stones, pancreatitis, lupus erythematosus, and hearing problems. In addition, people with diabetes should be aware that diuretics might increase blood sugar levels. People with heart or blood vessel disease should know that some diuretics increase cholesterol or triglyceride levels. The risk of an allergic reaction to certain diuretics is greater in people with bronchial asthma. Before using diuretics, people with any of these medical problems should make sure their physicians are aware of their conditions. Also, people who have trouble urinating or who have high potassium levels in their blood may not be able to take diuretics and should check with a physician before using them.
USE OF CERTAIN MEDICINES. Taking diuretics with certain other drugs may affect the way the drugs work or may increase the chance of side effects.
Some side effects such as loss of appetite, nausea and vomiting, stomach cramps, diarrhea, and dizziness, usually lessen or go away as the body adjusts to the medicine. These problems do not need medical attention unless they continue or interfere with normal activities.
Patients taking potassium-sparing diuretics should know the signs of too much potassium and should check with a physician as soon as possible if any of these symptoms occur:
- irregular heartbeat
- breathing problems
- numbness or tingling in the hands, feet, or lips
- confusion or nervousness
- unusual tiredness or weakness
- weak or heavy feeling in the legs
Patients taking diuretics that cause potassium loss should know the signs of too little potassium and should check with a physician as soon as possible if they have any of these symptoms:
- fast or irregular heartbeat
- weak pulse
- nausea or vomiting
- dry mouth
- excessive thirst
- muscle cramps or pain
- unusual tiredness or weakness
- mental or mood changes
Diuretics may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes a diuretic should let the physician know all other medicines he or she is taking and should ask whether the possible interactions can interfere with drug therapy. Among the drugs that may interact with diuretics are:
- Angiotensin-converting enzyme (ACE) inhibitors such as benazepril (Lotensin), captopril (Capoten), and enalapril (Vasotec), which are used to treat high blood pressure. Taking these drugs with potassium-sparing diuretics may cause levels of potassium in the blood to be too high, increasing the chance of side effects.
- Cholesterol-lowering drugs such as cholestyramine (Questran) and colestipol (Colestid). Taking these drugs with combination diuretics such as Dyazide and Maxzide may keep the diuretic from working. The person should take the diuretic at least one hour before or four hours after the cholesterol-lowering drug.
- Cyclosporine (Sandimmune), a medicine that suppresses the immune system. Taking this medicine with potassium-sparing diuretics may increase the chance of side effects by causing levels of potassium in the blood to be too high.
- Potassium supplements, other medicines containing potassium, or salt substitutes that contain potassium. Taking these with potassium-sparing diuretics may lead to too much potassium in the blood, increasing the chance of side effects.
- Lithium, used to treat bipolar disorder (manic-depressive illness). Using this medicine with potassium-sparing diuretics may allow lithium to build up to poisonous levels in the body.
- Digitalis heart drugs such as digoxin (Lanoxin). Using this medicine with combination diuretics such as triamterene-hydrocholorthiazide (Dyazide, Maxzide) may cause blood levels of the heart to be too high, making side effects such as changes in heartbeat more likely.
The list above does not include every drug that may interact with diuretics. The patient is advised to check with a physician or pharmacist before combining diuretics with any other prescription or nonprescription (overthe-counter) medicine.
AHFS: Drug Information. Washington, DC: American Society Healthsystems Pharmaceuticals, 2002.
Drug Facts and Comparisons. St. Louis: Facts & Comparisons, 2003.
Reynolds, J. E. F., ed. Martindale: The Extra Pharmacopeia, 31st ed. London: The Pharmaceutical Press, 1993.
Nancy Ross-Flanigan Sam Uretsky, PharmD
Last Updated: 01/28/2009
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