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Best Edema Diuretics: Loop vs. Osmotic

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Medications that help the body release water through increased urination are called diuretics. They are sometimes referred to as water pills. There are several types of diuretics including loop, potassium-sparing, thiazide, and osmotic. Below is an overview of loop diuretics and osmotic diuretics and a comparison of the two.

What are Loop Diuretics?

Loop diuretics can be either administered via I.V. in a hospital setting or taken orally. They increase urine flow and remove water from the body better than any other diuretic. Because they are more powerful than thiazide diuretics, they are more effective in treating patients with impaired kidney function.

How do Loop Diuretics work?

These medications, act at the ascending Loop of Henle (a tiny, loop-like filtering tube in the kidney nephrons) which increases urine production. Specifically, loop diuretics prevent the reabsorption of sodium ions. This, in turn, increases electrolyte concentration in the fluid that passes through the nephron.

Because this concentrated water cannot be put back into the bloodstream from the nephron, sodium reabsorption is inhibited. This causes water to be lost through increased urine volume and urination frequency.

Uses of Loop Diuretics

These powerful medications are mainly used to treat edema (swelling) in hospital patients who suffer from congestive heart failure, liver disease, and kidney disease. Since loop diuretics reduce blood volume which also decreases blood pressure, they are sometimes used to treat hypertension (high blood pressure). This is especially true in patients with congestive heart failure.

Here is a list of loop diuretics and their uses:

  • Furosemide (Lasix) - The first loop diuretic to be approved in the United States. It is still commonly used to treat fluid build-up related to liver scarring, heart failure, or kidney disease. Also used to treat high blood pressure.
  • Torsemide (Demadex) - Used to treat both high blood pressure and edema.
  • Bumetanide (Bumex) - Most commonly used to treat heart failure. Frequently used for patients who don't respond to furosemide or other diuretics. Also sometimes used to treat edema.
  • Ethacrynic acid (Edecrin) - Although still available, the second loop diuretic approved for use in the United States is not frequently used. It is used to treat high blood pressure and edema from liver failure, kidney failure, and congestive heart failure.

Risks and Side Effects of Loop Diuretics

Some people may experience the following side effects when taking loop diuretics:

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

Additionally, some loop diuretics (furosemide, torsemide, and bumetanide) are sulfa drugs(sulfonamides). People who are sensitive to sulfa drugs may also be sensitive to these three medications. 

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

What are Osmotic Diuretics?

Osmotic diuretics are the least used type of diuretics. They work by increasing osmolality (the concentration of osmotically active particles in a solution). Osmotics reduce osmotic pressure in the blood and blood vessels. This inhibits, “the reabsorption of water and dissolved substances, and causes an increase in urine flow.”

How does an Osmotic work?

Osmotic diuretics expand the body's fluid and plasma volume which increases blood flow to the kidneys. They also inhibit the reabsorption of water and sodium and increase, the osmolarity of blood and renal filtrate. These diuretics draw fluid from the cells of the brain and eyes which reduces pressure on those parts of the body. They can also increase the elimination of renal toxins through the urine from drugs (both legal or illegal).

Osmotics are given intravenously to treat:
Cerebral edema - swelling of the brain
Acute glaucoma - eye conditions that damage the optic nerve
Acute/oliguric renal failure (kidney failure)
Drug overdose - from both legal and illegal drugs

This class of diuretics is contraindicated for generalized edema (swelling). If used to treat edema, osmotic diuretics could make the swelling worse.

A few osmotic diuretics and their common uses:
Mannitol - The most commonly used osmotic. It decreases pressure in the eyes and brain.
Glycerin (also glycerine or glycerol) - Taken orally, it can rapidly reduce internal pressure in the eye. Useful in the emergency treatment of elevated eye pressure.
Isosorbide - Used mainly to treat hydrocephalus (accumulation of cerebrospinal fluid within the brain) and glaucoma.
Urea - A carbonic acid found in urine, blood, and lymph, Urea is also synthesized and given intravenously to treat pressure in the brain or eyes.

Risks and Side Effects of Osmotics

Some of the side effects of osmotic diuretics include:

  • Headaches
  • Nausea and vomiting
  • Electrolyte imbalance
  • Pulmonary edema (swelling)
  • Dehydration and loss of free water
  • Tachycardia - a faster than normal resting heart rate resulting from losing fluids rapidly
  • Hyponatremia - increased sodium levels
  • Extracellular volume expansion, a serious problem in individuals with heart failure or pulmonary edema


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