What Are Diuretics? - Definition, Types, Side Effects & Examples

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  • 0:00 Definition of Diuretics
  • 1:30 Types & Examples of Diuretics
  • 4:00 Side Effects of Diuretics
  • 5:15 Lesson Summary
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Lesson Transcript
Instructor: Rachel Torrens
What is a healthcare provider to do when a patient needs to have less fluid in his body? Diuretics to the rescue! Find out more about this important class of medications, its uses, and side effects, in this lesson.

Definition of Diuretics

Diuretics are a type of medication used to increase the amount of water released from the body in a patient's urine. In fact, diuretics are commonly known as water pills.

Now to explain how diuretics work, we are going to take a trip back in time to your 8th grade science class. Remember the term 'osmosis?' I bet you thought you would never need to use it, but this is exactly the principle upon which kidneys filter and diuretics work. Generally speaking, the process of osmosis goes like this: water naturally flows from an area of lower concentration to higher concentration making the overall solutions equal in concentration.

The kidneys are no different: they reabsorb electrolytes (mainly sodium, potassium and calcium). Due to osmosis, the water naturally follows the electrolytes to establish an equal concentration of solutes on either side of the semipermeable membrane in the kidney. So, what diuretics do is block the reabsorption of electrolytes. If the electrolytes are not reabsorbed into the body but stay in the urine, then voila! The water stays in the urine and is excreted as well, thereby, decreasing the amount of overall fluid in a patient.

There are several reasons a healthcare provider may wish to decrease the overall volume of liquid in a patient, including high blood pressure, heart failure, edema (fluid retention), and liver or kidney disease.

Types & Examples of Diuretics

There are three main types of diuretics. Each targets a different part of the kidneys and causes increased water excretion:

1. Thiazide Diuretics

Thiazides are commonly used to treat high blood pressure (hypertension) and are often the first medication patients are placed on to manage this condition. Thiazide diuretics target the distal tubule of the kidneys preventing them from reabsorbing sodium back into the body; therefore, the sodium is excreted in the urine. And wherever sodium goes, potassium is sure to follow!

Water is drawn out with the electrolytes into the urine. Thus urine output is increased, and the overall blood volume in the patient is decreased. Also, thiazides are the only diuretics to cause widening of the blood vessels (vasodilation), which is why it is so useful in managing hypertension. Some examples of thiazide diuretics include Chlorothiazide (Diuril), Hydrochlorothiazide (Microzide), and Metolazone (Zaroxolyn).

2. Loop Diuretics

This type of diuretic is most commonly used in managing heart failure, edema, and kidney disease. A loop diuretic acts similarly to a thiazide, prompting sodium, potassium and therefore water to be excreted in the urine. However, some key differences exist. First, it targets the Loop of Henle in the kidney. Secondly, it is an especially potent diuretic, causing a high volume of urine to be excreted. Some examples of loop diuretics include Furosemide (Lasix) and Torsemide (Demadex).

3. Potassium-sparing Diuretics

For some patients, loop and thiazide diuretics are dangerous because they cause the patient to lose not only sodium and water in the urine, but potassium, too. If a patient's blood potassium is too low (hypokalemia), it can lead to complications, especially if the patient has an underlying heart condition, or kidney or liver dysfunction. Therefore, potassium-sparing diuretics were created. These diuretics cause only sodium and water to be excreted, but keep potassium from following suit. These medications are used to treat patients with heart failure, liver disease, or kidney disease. Some examples of potassium-sparing diuretics include Spironolactone (Aldactone) and Triamterene (Dyrenium).

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