Drugs that increase the volume of urine and that are used to remove excess fluid from the body
Loop diuretic drugs
Potassium-sparing diuretic drugs
Other diuretic drugs
Diuretic drugs are commonly used in the treatment of high blood pressure (see Hypertension) and chronic heart failure. Diuretics are also used to treat other conditions in which excess fluid accumulates in the body, such as liver or kidney disorders and glaucoma. Acetazolamide may be used to prevent altitude sickness and to treat the inner ear condition Ménière’s disease.
How do they work?
Diuretics act on the kidneys to increase the volume of water that is excreted from the body as urine. Water, salts (such as sodium and potassium), and waste products are removed from the blood as it passes through small tubules in the kidneys. Most of the water and salts are reabsorbed into the bloodstream. What is not reabsorbed is then excreted, along with waste products, as urine. Diuretics reduce the reabsorption of water and salts into the blood, thereby increasing the volume of urine that is produced. This action of diuretics relieves the accumulation of fluid that occurs in the body due to heart failure, and the reduced blood volume helps to reduce blood pressure. Some diuretics also dilate (widen) blood vessels in the body, which also has the effect of lowering blood pressure.
What are the types?
The diuretic drugs that are most frequently prescribed are thiazide drugs, loop diuretic drugs, and potassium-sparing diuretic drugs, which vary in their potency. Different types of diuretic affect reabsorption at different sites along the kidney tubules. The type of diuretic that your doctor prescribes is likely to depend on the condition being treated, your age, and any other existing medical conditions that you may have.
These are the most commonly used diuretics for the treatment of high blood pressure. Thiazides lower blood pressure by reducing blood volume as well as by dilating (widening) blood vessels. These types of diuretic are usually taken orally once a day and have an effect at low doses.
Thiazides generally cause few side effects. However, the increased frequency with which you need to pass urine may be inconvenient. This effect is most noticeable at the start of treatment. You may find it convenient to take the diuretic early in the morning so that your sleep is not interrupted at night.
Occasionally, thiazide diuretics cause light-headedness due to a drop in blood pressure. Thiazides can cause excessive loss of potassium from the body, which can result in confusion, weakness, and, in rare cases, an abnormal heart rhythm. Blood tests are used to monitor the levels of potassium in the body. To correct low levels, you may be given a potassium supplement or a potassium-sparing diuretic either in place of or in combination with a thiazide.
Thiazides may also cause increased levels of uric acid in the blood. When the level of uric acid becomes too high, crystals may be deposited in the joints, which may cause the painful condition gout. Thiazides are sometimes avoided in people with diabetes mellitus because they may make control of the condition more difficult. In addition, these drugs can cause the skin to become sensitized to sunlight.
These diuretics have a more powerful effect than thiazides and are used to treat the accumulation of fluid due to heart failure, some kidney disorders, and some liver disorders. They may also be given as an injection for the emergency treatment of acute heart failure.
Loop diuretics cause the production of urine to increase dramatically. In men with an enlarged prostate gland, this problem may lead to urinary retention. The drugs may also cause nausea. In addition, loop diuretics can deplete the body’s supply of potassium. If you are affected by potassium loss, your doctor may prescribe a potassium supplement or a potassium-sparing diuretic to be taken in combination with a loop diuretic.
Most of these drugs are mild diuretics and are used either alone or in combination with a thiazide or loop diuretic if potassium depletion has occurred. The side effects of potassium-sparing diuretics may include digestive disturbances, such as flatulence and nausea, a dry mouth, and rashes. One drug, spironolactone, may cause breast enlargement in men (see Gynaecomastia).
Other diuretic drugs
Acetazolamide is occasionally used to prevent altitude sickness and attacks of dizziness associated with the inner ear condition Ménière’s disease, and to relieve the excessive pressure in the eye that occurs in glaucoma. Mannitol may also be used to reduce pressure in the eye in glaucoma and to treat cerebral oedema (a build-up of fluid in the brain).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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