Diuretic

2010-02-10T23:09:00.000-08:00

Diuretics, also known as water pills, lower blood pressure by forcing the body to rid itself of salt and water through the kidneys into the urine. They rid the body of more or less salt and water depending on where they’re active in the kidneys. After a couple of months, the body overcomes the reduction in body fluids. At this point, the reduction in the resistance to blood flow accounts for the ongoing fall in blood pressure.

Anyone taking diuretics is encouraged to use sunscreen, avoid tanning booths and drink plenty of water when out in the sun. Furthermore, some patients may be encouraged by their physician to increase the amount of potassium in their diet and may be placed on potassium pills. Foods rich in potassium include bananas, salmon, melons, almonds, potatoes and spinach. Grapefruit juice is also high in potassium but is not recommended for people who are taking diuretics.

Diuretics are divided into different groups according to where they act along the nephron (the functional units in the kidney that remove waste and excess substances from the blood) as follows.

Thiazide and thiazidelike diuretic group

Although they’re not the most effective drugs for ridding the body of excess salt and water, this group is the most effective for lowering blood pressure. This group acts at the distal tubule (a part of the nephron where water and waste exchange occurs) to increase the excretion of sodium and chloride.

Thiazide diuretics, the most effective blood-pressure-lowering drugs, have been prescribed for more than 40 years It can lower the blood pressure about 15 mm Hg systolic and 7 mm Hg diastolic.

Common side effects of thiazide diuretics are as follows:

• Initially induce sleep loss due to urination (but this side effect is offset by taking medication early in the day)

• Reduce calcium excretion in the urine and may provoke elevated blood calcium levels

• Are not recommended during pregnancy and breast-feeding

• In higher dosage, cause excessive potassium loss, increase serum cholesterol, and increase the body’s resistance to its own insulin (resulting in an increased intolerance to glucose, the sugar in the blood) Thiazides may increase a person’s tendency toward diabetes.

• Causes problems with erection in men, especially in higher dosages

• Reduces the activity of certain drugs, especially insulin, anticoagulants (blood thinners), drugs to reduce uric acid in the blood, and sulfonylureas (antidiabetic drugs with names such as chlorpropamide, tolazamide,and tolbutamide)

Most thiazide diuretics are taken once a day in the morning. Any reduction in blood pressure is maintained throughout the 24 hours by this once a day dose. But the effect of passing extra urine wears off within 12 hours. So, you will not have to get up in the night to make extra trips to the toilet. Indeed, the dose used to treat high blood pressure is quite low, and many people barely notice an increase in the amount of urine that they pass.

Loop diuretics

This group acts at the thick ascending limb of the loop of Henle, part of the kidney’s filtering mechanism. These drugs have a potent effect on salt and water elimination.

Loop diuretics are more effective than the thiazide diuretics for ridding the body of salt and water, but they don’t lower the blood pressure as much. Loop diuretics don’t raise the cholesterol the way that thiazide diuretics do (a definite advantage), but they’re not as effective in reducing disease and death caused by high blood pressure.

Loop diuretics reduce not only sodium and chloride but also calcium and magnesium. They’re potent enough to cause a serious fall in the blood sodium if used to excess, and they can cause significant potassium loss. These dangers of loop diuretics make them less useful than thiazide diuretics in the treatment of high blood pressure. Other problems associated with the loop diuretics include:

• Hearing loss or a ringing in the ears

• Serum uric acid increase with possible development of gout, a painful swelling of certain joints, especially the big toes

• Reactions in people who are hypersensitive to several sulphur-containing antibiotics and sulfonamides (this includes several drugs for treatment of diabetes like diabinase and tolinase).

Use during pregnancy and breast-feeding is probably not a good idea, but you can discuss this with your doctor.

Most loop diuretics are taken once a day in the morning. The effect of making more urine starts within half an hour. So, you may find you need to go to the toilet a couple of times within a few hours of taking the tablet. However, the effect of passing extra urine wears off within a few hours.

Potassium-sparing diuretics

This group functions at the late distal tubule and the collecting tubule (key parts of the nephron’s exchange system). The result is only a mild increase in sodium excretion and chloride excretion but a tendency to reduce the excretion of potassium. Because the other diuretics cause potassium loss, these potassiumsparing diuretics are important for maintaining body potassium.

Potassium-sparing diuretics have little effect on salt and water or lowering blood pressure, but in combination with other diuretics, they conserve the body’s potassium. Therefore, they’re often manufactured with a diuretic.

Their ability to conserve potassium is also their greatest danger — an abnormal elevation of the blood-potassium level — so they should never be used when the potassium is already high. People with diseases such as kidney failure are at a particularly high risk for this complication. These drugs also decrease the loss of calcium and magnesium associated with the other diuretics.

Aldosterone-antagonist group

This group blocks the action of aldosterone, a natural hormone that causes salt and water retention, so that more salt and water is excreted into the urine while potassium loss is reduced. These drugs could be included in the potassium-sparing group, but they lower blood pressure in an altogether different manner than the potassium-sparing group — they deactivate aldosterone.

Aldosterone-antagonist diuretics do not directly cause loss of salt and potassium in the urine. Instead, they block the action of the steroid hormone aldosterone, which causes salt and water retention. As a result, these diuretics cause salt and water loss only if aldosterone is present. At the same time, they conserve potassium, so these are also potassium-sparing drugs.

They must be used carefully when potassium is already elevated or when the patient is taking a drug that tends to raise potassium. All the dangers of high potassium for the potassium-sparing diuretics apply to aldosterone-antagonist diuretics.

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Diuretic