Loop Diuretics

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What are loop diuretics and what are they used for?

A diuretic is a drug which increases the amount of water that you pass out from your kidneys. (A diuretic causes a 'diuresis' - an increase in urine.) So, they are sometimes called 'water tablets'. There are different types of diuretics. Loop diuretics are one type. They include furosemide (frusemide), bumetanide and torasemide. Each comes in different brand names.

Loop diuretics are a common treatment for heart failure. In this condition, fluid accumulates in your body due to the heart not pumping blood around the body as well as normal. So, you may become breathless (as fluid accumulates in the lungs) and your ankles and legs may swell with extra fluid in the tissues (oedema). Loop diuretics are also used to treat other conditions which cause fluid to build up in the body such as certain liver and kidney disorders. They are also sometimes used to treat high blood pressure. (But, a different type of diuretic called a thiazide diuretic is more commonly used to treat high blood pressure.)

How do loop diuretics work?

They work by making the kidneys pass out more fluid. They do this by interfering with the transport of salt and water across certain cells in the kidneys. (These cells are in a structure called the loop of Henle - hence the name loop diuretic. You have thousands of these loops in each kidney.) As more fluid is passed out by the kidneys, less fluid remains in the bloodstream. So any fluid which has accumulated in the tissues of the lungs or body is drawn back into the bloodstream. This eases symptoms such as oedema and breathlessness caused by the congestion of fluid.

What are the possible side-effects?

When routine low doses are used, side-effects are uncommon. The salt balance in the bloodstream is sometimes upset which can cause a low blood level of potassium, sodium, and magnesium, and a high level of calcium. These effects may cause weakness, confusion, and rarely, abnormal heart rhythms to develop. You may be advised to have a blood test to check for these problems. If you have diabetes or gout, these conditions may be made worse by diuretics.

Other possible side-effects include: an upset stomach, dizziness on standing (due to too low blood pressure). The risk of side-effects increases with increasing dose. Read the information leaflet which comes with your particular brand for a full list of possible side-effects.

Other considerations

Most loop diuretics are taken once a day in the morning. The effect of making more urine starts within half an hour. So, you may find you need to go to the toilet a couple of times within a few hours of taking the tablet. However, the effect of passing extra urine wears off within a few hours. So, you will not have to get up in the night to make extra trips to the toilet.

You can generally take the dose at a flexible time to suit you. So, for example, if you want to go out early in the morning for a few hours and dont want to have to find a toilet, you may be able to postpone the dose till later on in the day when it may be more convenient to find toilets.

© EMIS and PIP 2006   Updated: October 2006

The authors and editors of this article are employed to create accurate and up to date content reflecting reliable research evidence, guidance and best clinical practice. They are free from any commercial conflicts of interest. Find out more about updating.

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