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High Blood Pressure Medications: Loop Diuretics

Updated on September 16, 2012

High blood pressure remains one of the most prevalent medical problems in our population. Hypertension, as it is also known, is defined as blood pressure that is over normal limits for age.

The parameters for "normal" have changed a bit over time, and so have the recommendations for treatment. But, one of the mainstays of therapy continues to be "loop diuretics".

You may have never heard this term, or may have heard your doctor mention it in passing. More likely you would recognize the names of some of the more common anti-hypertensives in the class of loop diuretics.

The phrase "loop diuretic" describes the type of medication and where it works in the body, although this may not be immediately obvious.

NEPHRON Diagram Showing Collecting System

Diagram of the complicated urine collecting (yellow) system in the nephron, the functional unit of the kidney. The loop of Henle is represented by the number 7. Arterioles are red and venous components are blue.
Diagram of the complicated urine collecting (yellow) system in the nephron, the functional unit of the kidney. The loop of Henle is represented by the number 7. Arterioles are red and venous components are blue. | Source

What Does "Loop" Mean in Loop Diuretic?

The kidney is the organ responsible for making urine. The process is very complicated and involves balancing electrolytes and fluid before sending liquid waste on to be eliminated from the body. The nephrons are the subunits of the kidney that are largely responsible for this complex biologic function, with each kidney having hundreds of thousands of nephrons.

The nephrons are comprised of an interwoven web of blood vessels and tubules. Among the contents of the fluid passing through are waste products and electrolytes. Complex chemical reactions cause the body to reabsorb the needed electrolytes back into the blood stream from the tubules. This web sends fluid and chemicals back and forth until a proper balance is reached inside the body. Excess is eliminated.

The "loop" part of the name is referring to the 'loop of Henle' in the nephron of the kidney. The waste and extra fluid continue along the tube system and are eventually excreted as urine.

The loop of Henle plays an important role in balancing both fluid and salt in the body.

What is a Diuretic?

A diuretic medication causes diuresis- increased urine excretion from the body.

There are several different types of diuretic medicines that act in various ways and locations in the body.

As already stated, loop diuretics work in the loop of Henle of the nephron in the kidney. Loop diuretics increase the amount of fluid secreted by the body.

How a Loop Diuretic Works for High Blood Pressure

One of the features of high blood pressure for many people is the abnormal accumulation of sodium chloride (salt) and extra fluid in the body.

A diuretic helps eliminate this salt and extra fluid, thereby decreasing blood pressure.

The loop of Henle is a specialized part of the "collecting system" of the kidney. As fluid and dissolved particles, such as electrolytes (sodium, potassium, etc) move through the collecting system tubes, they are subject to either staying in the tubes to be excreted from the body, or being reabsorbed into the blood circulation.

There are complicated mechanisms at play to determine where and when each particle is reabsorbed into the body (or not). The concentration of electrolytes (including sodium chloride), various hormones and other signals control this process. The same is true for fluid balance and the amount and concentration of urine that ends up being excreted.

The loop of Henle has special channels or passageways for fluid and electrolyes to pass through to re-enter the circulation of the blood stream. Loop diuretics block this channel. The result is that the fluid and electrolytes stay in the tubules and eventually leave the body as urine.

Therefore, diuretic medicines cause more urine excretion and loss of fluid from the body than would normally occur.

Therefore diuretics eliminate salt and fluid from the body. This has the effect of causing blood pressure to decrease.

A Closer Look at the Nephron of the Kidney. Loop diuretics block the reabsorption of water and some electrolytes from getting back into the body at the loop of

Examples of Loop Diuretic Medicines

Generic Name
Brand Names (common)
Most commonly prescribed.
Used intravenously in the hospital for heart failure.
ethacrynic acid
Very potent, only to be used under close medical supervision
Can be used in pregnancy

Side Effects and Complications of Loop Diuretics

ELECTROLYTE IMBALANCE: Because electrolytes are lost along with fluid, there is the possibility of losing too many electrolytes. This is especially true for potassium. Usually, a potassium supplement will be prescribed with a loop diuretic. Potassium levels will be checked while the body is getting used to this medication and then periodically while on the medicine.

DEHYDRATION: Too much fluid can be lost, especially when starting these medicines, and until the correct dose is discovered.

HYPOTENSION: Because of the changes in electrolytes and possible dehydration, the blood pressure may drop too low. Following up with your doctor is necessary while starting or taking these medicines.

The most common side-effects reported by patients which may be due to one or more of the above effects include:

  • headache
  • lightheadedness
  • fatigue
  • diarrhea

Uncommon side effects include:

  • Abnormal heart rhythms (due to electrolyte imbalance)
  • Severe diarrhea
  • Hearing loss

Warning & Disclaimer

Although the author of this article is a physician, the subject matter presented here is introductory and for information only. Always consult your personal physician for questions about medical conditions or medications as there are many complex and individual factors that influence medical decision-making.

This article in no way should be interpreted as medical advice. It is not comprehensive and provides no diagnostic indicators, nor prescribing information.


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    • Melovy profile image

      Yvonne Spence 5 years ago from UK

      My father was just talking about blood pressure a few days ago. He had hypertension, but the medication he was on for cancer made his blood pressure drop and he had blackouts. So he was taken off the blood pressure medication and then was getting swelling and water retention. I had no idea until he said this that diuretics were often used for hypertension. I'm not sure what he's on now, but he's monitored closely.

      As well as finding this article interesting, I was also interested in Marcy's comment. I also tend towards low blood pressure and my mother used to be the same. However, at 81 she now has hypertension, so it seems that even those of us with low blood pressure need to be careful with salt.

    • Marcy Goodfleisch profile image

      Marcy Goodfleisch 5 years ago from Planet Earth

      My mother had this condition, but I don't know much about it - I guess I should learn soon, because more and more people are getting it. My own blood pressure is low (I keep saying salt keeps me alive, but I know that probably makes you cringe when you read it!).

      Very interesting hub - voted up and up!