Loop Diuretics: Examples & Side Effects

Instructor: Heather Zonts

Heather has taught in AD and BSN Nursing programs and has a master's degree in nursing.

This lesson will provide a brief overview of the mechanism of action of loop diuretics. It will also discuss examples of loop diuretics and side effects of these medications.

Mechanism of Action

Diuretics are sometimes called water pills because they eliminate fluid from the body through the kidneys. Loop diuretics specifically are medications that act on the ascending portion of the loop of Henle in the kidneys. They increase the reabsorption of water by inhibiting the reabsorption of sodium; therefore, increasing the amount of fluid eliminated by the kidneys. Loop diuretics are not selective. They take everything, including important electrolytes such as potassium. This becomes important when discussing side effects of this family of medications. Because of this mechanism of action, loop diuretics are used to treat individuals with increased circulating fluid, such as individuals with congestive heart failure that have swelling in the lower extremities or fluid in their lungs.

This picture shows the blood flow through the nephron of the kidney. You can see that the loop of Henle is at the end of the system and leads directly to the ureters. The ureters eliminate urine from the kidneys.

Examples of Loop Diuretics

Lasix (furosemide) - 1st loop diuretic created. According to the National Institutes of Health (2015), approximately 37 million prescriptions are filled yearly for this medication. It is available as a table, liquid suspension for oral ingestion, and for intravenous administration.

Bumex (bumetanide) - Available in tablet form.

Demadex (torsemide) - Available in tablet form and liquid form for intravenous administration.

Edecrin (ethracrynate) - Rarely used in the United States. Available in tablet form and liquid form for intravenous administration.

Side Effects

Now consider the mechanism of action, eliminating fluid and electrolytes from the body. What type of side effects would you expect to see? How does the body get rid of fluid?

Increased frequency of urination - The body eliminates fluid through the creation of urine. Therefore, the more urine you create, the more you need to urinate. Individuals taking loop diuretics will typically experience an increased frequency of urination.

Dehydration - Now, the more fluid you eliminate the more likely you are to eliminate too much. If too much fluid is eliminated, the body becomes dehydrated. When you become dehydrated, your organs must work harder, especially the kidneys. If you become dehydrated, you will experience increased thirst as well as concentrated urine. Thirst is how our bodies tell us we need fluid. The urine becomes concentrated because the kidneys are not able to pull fluid out of the circulating system; therefore, you are only eliminating waste products. This also requires the kidneys to work harder, meaning if it is not corrected early damage to this organ can occur.

Low blood pressure - Also, the more fluid your kidneys remove from the circulating system, the less pressure there is in your blood vessels leading to low blood pressure. To try to understand this, think about a hose. If it is turned on high, the hose is expanded completely and you have increased pressure. Now, if you only turn the hose on low, you will have less flow through the hose and the hose will not have fluid pushing against all surfaces because of decreased water pressure. The same thing happens with decrease circulating fluid, the blood pressure decreases.

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