Diuretics, commonly known as ‘water pills’ are drugs that encourage the kidneys to move body salt and water into the urine. Along with these changes, the pressure inside the blood vessels is decreased and the blood pressure goes down.
Diuretics can be used to treat heart failure that occurs when the heart’s pumping action has weakened. In treating this disorder, diuretics reduce the amount of fluid that accumulates in the tissues and the lungs. Also, a resulting drop in blood volume decreases how hard the heart must pump. Diuretics may also be prescribed for other conditions such as nephrotic syndrome (a kidney disease that causes swelling), liver disease (causing fluid accumulation in the abdomen), premenstrual syndrome (when hormone changes cause fluid build-up and bloating) and sometimes in glaucoma (when fluid pressure builds up in the eye). In some cases, they are used to remove calcium when too much accumulates in the body.
The kidneys act as filters. Through this process, they remove water, salts (mainly sodium and potassium) and waste products from the blood. Most of the water and salts are returned to the bloodstream by a process called reabsorption but certain amounts along with the waste products are passed as urine. Diuretics reduce the amount of water and salts returned to the bloodstream thereby increasing the amounts in the urine produced.
Thiazide Diuretics - These are the most common diuretics prescribed by doctors. Thiazides cause the kidneys to increase the amount of sodium, potassium and volume of water they put out. Due to the extra potassium passed in urine, these diuretics may lead to too little potassium in the body. To prevent this, a potassium-supplement or a potassium-sparing diuretic is sometimes prescribed along with the thiazide diuretics. The most commonly prescribed thiazide diuretic is hydrochlorothiazide (Hydrodiuril™). A group of drugs that are chemically unrelated to the thiazides but have very similar actions are chlorthalidone (Hygroton™), indapamide (Lozide™) and metolazone (Zaroxolyn™).
Loop Diuretics - Like the thiazides, these diuretics reduce the amount of sodium, potassium and water reabsorbed by the kidneys. The loop diuretics tend to be faster-acting and produce a larger volume of urine but less blood pressure lowering than the thiazides. They too can cause extra potassium loss that may need to be prevented as is done with thiazide diuretics. The most common loop diuretic is furosemide (Lasix™).
Potassium-Sparing Diuretics - This type of diuretic interferes with the reabsorption of only sodium and water from the kidneys, thus the name of potassium-sparing. Their diuretic action tends to be milder than the thiazide and loop diuretics. Potassium-sparing diuretics are usually used with the thiazide or loop diuretics to prevent too much potassium loss from the body. Three common potassium-sparing diuretics are spironolactone (Aldactone™), amiloride (Midamor™) and triamterene (Dyrenium™). Combinations of diuretics are hydrochlorothiazide triamterene (Dyazide™) and hydrochlorothiazide/amiloride (Moduret™).
Acetazolamide (Diamox™) - This is a drug with a mild diuretic activity that is often prescribed for the treatment of glaucoma to reduce pressure in the eyes.
Potassium Depletion - As discussed earlier, some diuretics can cause a decrease in the potassium levels in the body. This may cause you muscle weakness, fatigue, dizziness or irregular heart rhythms. This is especially a concern if you take the heart medication digoxin (Lanoxin).
Potassium levels are something that can only be monitored by a blood test. If you have heart problems or are taking digoxin you may need routine blood testing. The deficiency can be corrected by adding a potassium-sparing diuretic, a potassium supplement or a diet rich in potassium.
Potassium Supplements - Although most diets contain enough potassium, a doctor may advise a supplement if you take thiazide or loop diuretics. Potassium supplements are available in tablet or capsule form from a pharmacist.
Potassium From Food - Changes in diet should only be made with a doctor's advice. Food choices can alter the amount of potassium in your diet.
Keeping Blood Pressure in Balance - The doctor will likely take your blood pressure at regular intervals to make sure the medication is effective. You should rise slowly from a sitting or lying position to allow your blood pressure to adjust. Otherwise you may feel dizzy or faint.
Other Effects on the Body - Check with your pharmacist or doctor before taking over-the-counter cold medications. Some have ingredients that can raise blood pressure. Some diuretics, especially hydrochlorthiazide (Hydrodiuril™) can cause your skin to become sensitive to sunlight resulting in sunburn. Some diuretics may increase uric acid levels in the blood and should be avoided by anyone having trouble with gout. Diuretics may also raise blood sugar levels which could cause problems for those with diabetes.
Before new medications are prescribed, your doctor should be told if you have other medical conditions. If you often have diarrhea or vomiting, causing you to lose large amounts of fluid, you may become dehydrated. Your doctor should be told right away if this is happening.
As diuretics only control and do not cure hypertension, they may need to be taken for the rest of your life. Get into the habit of taking the medication at the same time each day so you do not forget. If you miss a dose, take it as soon as possible. If it is close to the time for the next dose, do not double the amount.
Sometimes you may have an upset stomach from taking the medication. Taking it with food may reduce this unwanted effect. Since diuretics increase urine production, they are best taken in the morning to avoid a disturbed sleep from a full bladder.
Potassium supplements can also have these unwanted side effects on the stomach. Diarrhea, stomach pain, and gas often result from their use. Taking each dose after a meal can also ease the negative effects on the stomach.
Diuretics are a valuable part of controlling blood pressure. They are not a cure. In addition to treatment with medications, your doctor may suggest dietary changes, meditation, exercise and weight loss to help control your blood pressure. As with all drug therapies, it is important to ask your pharmacist or doctor how you can get the most benefit from your medication. Asking questions and understanding your condition helps to put you in control of your health.