A diuretic is a drug that removes excess water from the body by increasing the production of urine by the kidneys. Alcohol and caffeine, for example, are mild diuretics. By reducing the amount of water in the circulation, diuretic drugs reduce edema (fluid retention in tissues) that cause breathlessness and ankle swelling in heart failure, nephrotic syndrome (a kidney disorder), and cirrhosis of the liver.
Diuretic drugs lower the blood pressure and are therefore commonly to treat high blood pressure (hypertension). Carbonic anhydrase inhibitors (see below) are sometimes used to treat glaucoma (abnormally high fluid pressure in the eyeball).
Types of diuretic drugs
The various types of diuretic drugs differ markedly in their speed and mode of action.
These diuretics cause moderate diuresis (increased urine production) and are suitable for prolonged use. They act on the last part of the kidney tubules to reduce reabsorption of sodium into the bloodstream.
So-called because they act on a region of the kidneys known as Henle's loop (blocking sodium and chloride reabsorption), these are fast-acting, powerful drugs, especially when given by injection. Loop diuretics are particularly useful as an emergency treatment for heart failure.
These are often used along with thiazide and loop diuretics, both of which may cause potassium deficiency.
Carbonic anhydrase inhibitors
Drugs that block the action of carbonic anhydrase (an enzyme that affects the amount of bicarbonate ions in the blood); these diuretic drugs cause moderate diuresis but are effective only for short periods.
These are powerful diuretics that are used to maintain urine production after serious injury or major surgery. They act on the first part of the kidney tubules to reduce water reabsorption into the bloodstream.
Possible side effects
Diuretic drugs may cause chemical imbalances in the blood, most commonly hypokalemia (low levels of potassium in the blood). Symptoms of this condition include weakness, confusion, and heart palpitations. Treatment usually consists of a course of potassium supplements or a potassium-sparing diuretic drug. A diet rich in potassium (containing plenty of fruits and vegetables) may be helpful.
Some diuretic drugs may raise the level of uric acid in the blood, and thus increase the risk of gout. Certain types of diuretics increase the blood sugar level, an effect that can cause or aggravate diabetes mellitus.