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Best Edema Diuretics: Loop vs. Thiazide

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Diuretics help the body get rid of water through diuresis or increased urination. Some people refer to these medications as ‘water pills.’ There are several types of diuretics. Below we compare two of these medications, loop and thiazide diuretics.

What are Loop Diuretics?

Loop diuretics used in either oral form or through an I.V. in a hospital setting. The medication increases urine flow and removes water from the body, something loop diuretics do better than any other diuretic. Loop diuretics are also more powerful than thiazide diuretics making them more effective for treating patients with impaired kidney function.

What do Loop Diuretics do?

Specifically, loop diuretics are diuretics that act at the ascending Loop of Henle in the kidney, resulting in increased urine production. Their effect on the Loop of Henle (a tiny, loop-like filtering tube in the kidney nephrons) gives the medication its name.

Loop diuretics prevent the reabsorption of sodium ions which increases electrolyte concentration of the fluid that passes through the nephron. When water is more concentrated, it cannot be put back into the bloodstream from the nephron. Inhibiting sodium reabsorption then causes water to be lost as urine. This increases urine volume and urination frequency.

Uses for Loop Diuretics

Like other diuretics, loop diuretics cause the body to release water and reduce water retention. Loop diuretics are potent and useful for treating edema (swelling) in hospital patients suffering from a number of conditions including congestive heart failure, liver disease, and kidney disease.

One of the main effects of loop diuretics is reducing blood volume which decreases blood pressure. As a result, these drugs are sometimes used for treating hypertension (high blood pressure). Specifically, loop diuretics are frequently used to reduce blood pressure in patients with congestive heart failure.

List of loop diuretics:
Furosemide (Lasix) - The first loop diuretic to be approved in the United States (1966), Furosemide and is still widely used to treat fluid build-up associated with heart failure, liver scarring, or kidney disease. Also used to treat high blood pressure.
Ethacrynic acid (Edecrin) - The second loop diuretic approved for use in the United States (1967). It is still is available but is rarely used. Uses include treating high blood pressure and edema from congestive heart failure, liver failure, and kidney failure.
Bumetanide (Bumex) - Used for treating edema. It is most often used to treat heart failure and is frequently used in people for whom furosemide or other diuretics don’t work.
Torsemide (Demadex) - Used to treat both edema and high blood pressure. 

Risks and Side Effects of Loop Diuretics

Some of the common side effects of loop diuretics are:

  • Hyponatremia - low sodium levels
  • Hypokalemia - low potassium levels
  • Hypomagnesemia - magnesium deficiency
  • Hyperuricemia - abnormally high levels of uric acid in the blood
  • Gout - a type of inflammatory arthritis
  • Orthostatic hypotension (postural hypotension) - falling blood pressure when a person suddenly stands up from a lying or sitting position
  • Syncope - fainting
  • Dizziness
  • Dehydration

Some of the more infrequent side effects of loop diuretics include:

  • Dyslipidemia - an abnormal amount of lipids (fats) in the blood
  • Increased serum creatinine concentration
  • Hypocalcemia - low calcium in the blood
  • Metabolic alkalosis - tissue pH elevated beyond the normal range
  • Ototoxicity - ear damage which might be limited to tinnitus and vertigo, but could also result in deafness
  • Kidney failure (only in patients concurrently taking an NSAID and an ACE inhibitor)
  • Rash

Also, some loop diuretics (furosemide, torsemide, and bumetanide) are sulfonamides (sulfa drugs). Some individuals who are sensitive to sulfa drugs may also be sensitive to these loop diuretics.

What are Thiazide Diuretics?

Developed by Merck in the 1950s, thiazides were the first drug of their class to be approved. They are the most commonly used oral diuretics and are often used to treat high blood pressure (hypertension). Because they are weaker than some other diuretics (like loop diuretics), they are often preferred for lowering blood pressure.

Thiazides are also used to treat edema related to heart failure, liver failure, or kidney failure. These medications also help reduce the risk of heart attack, stroke, heart failure, and death due to hypertension. Both thiazides and thiazide-like diuretics are all available generically. In many places around the world, they are the cheapest drugs available for combating hypertension.

What do Thiazides do?

Thiazides act directly on the kidneys and increase urine flow:

by inhibiting the sodium/chloride cotransporter located in the distal convoluted tubule of the nephron (the functional unit of a kidney). Thiazides decrease sodium reabsorption which increases fluid loss in urine, which in turn decreases extracellular fluid and plasma volume.

One effect of thiazide is reduced cardiac output, meaning the heart doesn’t need to work as hard to pump blood around the body. This lowers the blood pressure. Thiazides also cause the body to lose potassium while retaining calcium which helps lower blood pressure.

A few thiazide diuretics include:
Chlorothiazide (Diuril) - Used to treat edema caused by renal dysfunction and to manage high blood pressure. Also used as an adjunct to treatment for edema associated with congestive heart failure or hepatic (liver) cirrhosis.
Chlorthalidone - Used to treat high blood pressure and different types of edema.
Hydrochlorothiazide (Microzide) - Used for treating high blood pressure and various types of edema.
Indapamide - Used alone or with other antihypertensive drugs to treat high blood pressure. It is also used to treat salt and fluid retention associated with congestive heart failure.
Metolazone - Used to treat high blood pressure, edema resulting from congestive heart failure, and edema caused by renal diseases.

Risks and Side Effects of Thiazides

The United States National Library of Medicine lists the following common side effects of thiazides and thiazide-like diuretics:

  • Nausea
  • Dizziness
  • Headaches
  • Dehydration
  • Polyuria - Excessive urination
  • Hyponatremia - low sodium in the blood
  • Hypokalemia - low potassium in the blood
  • Hypomagnesia - (magnesium deficiency)

Individuals with prolonged thiazide usage may also experience the following:

  • Hyperuricemia - abnormally high uric acid in the blood
  • Gout - a type of inflammatory arthritis
  • Possible increased risk of cholecystitis (gallbladder inflammation)
  • In rare instances, thiazides have been linked to liver injury


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