Potassium-sparing diuretics

What are potassium-sparing diuretics?

What is potassium?

Potassium (chemical symbol K) is a metallic element which is vitally important for our bodies to function. It is one of a group of substances called 'electrolytes' which carry a small electrical charge. This is important in transmitting nerve impulses and making muscles contract. Potassium is needed for all sorts of functions, including keeping your heart beating and your muscles working. We get potassium in the food we eat. Bananas are particularly high in potassium.

What is a diuretic?

A diuretic is a medicine which increases the amount of urine that you pass out from your kidneys. A diuretic causes an increase in urine (a diuresis). So, they are sometimes called 'water' tablets. There are three main types of diuretics:

• Loop diuretics (for example, furosemide). These are mostly used to treat heart failure. See the separate leaflet called Loop Diuretics for information.

• Thiazide diuretics (for example, bendroflumethiazide).These are mainly used for treating high blood pressure (hypertension) and fluid on the legs (oedema). See the separate leaflet called Thiazide Diuretics for more information.

• Potassium-sparing diuretics.

Potassium sparing diuretics examples

There are four potassium-sparing diuretics. They are:

• • Amiloride

  • Triamterene

  • Eplerenone

  • Spironolactone

Why are there potassium-sparing diuretics?

Sometimes when you take a diuretic, you lose too much potassium from your body along with the extra water you pass. This can make your potassium levels low, which can be quite dangerous. The potassium-sparing diuretics help to stop this happening. They can be used on their own but are most commonly used in combination with another type of diuretic. This is because they are not so strong as loop diuretics and thiazide diuretics.

How do potassium-sparing diuretics work?

Amiloride and triamterene 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. As more fluid is passed out by the kidneys, less fluid remains in the bloodstream. So any fluid which has built up in the tissues of the lungs or body is drawn back into the bloodstream to replace the fluid passed out by the kidneys. This eases symptoms such as fluid retention in the legs (oedema) and breathlessness caused by excess fluid on the lungs. As well as increasing the amount of water that you pass out from your kidneys, potassium-sparing diuretics also help your kidneys keep (retain) potassium in the body. They do this by blocking the channels that potassium would pass through.

Eplerenone and spironolactone work in a slightly different way to amiloride and triamterene. These medicines block the action of a hormone called aldosterone and this causes the kidney to pass out more fluid and keep potassium. This is why they are sometimes referred to as aldosterone antagonists.

When used on their own, potassium-sparing diuretics are weak diuretics. Loop diuretics and thiazide diuretics are stronger than potassium-sparing diuretics with regard to making the kidneys pass out more fluid. However, they also increase the amount of potassium passed out of the body through the kidneys.

Potassium-sparing diuretics are often combined with either a loop diuretic or a thiazide diuretic. This is because they help to keep the right amount of potassium in your blood and they help other diuretics to remove fluid from the body.

What are the main uses of potassium-sparing diuretics?

The main uses of potassium-sparing diuretics are:

• To prevent low levels of potassium (hypokalaemia) occurring when other diuretics are used (prescribed in combination with the other diuretic).

• In the treatment of heart failure. In this condition, fluid accumulates in your body, due to the heart not pumping blood around the body as well as it normally would. So, you may become breathless (as fluid accumulates in the lungs). Your ankles and legs may swell with extra fluid in the tissues (oedema). Other causes of oedema can also be helped by diuretics.

• In helping to reduce a condition called ascites where fluid builds up inside the tummy (abdominal) cavity. This can happen due to various conditions such as cirrhosis of the liver and certain kinds of cancer.

• In treating high blood pressure (hypertension), usually in combination with other medication.

What are the possible side-effects?

Side-effects are uncommon when routine low doses are used. The higher the dose, the greater the risk of side-effects developing. The leaflet which comes in the tablet package provides a full list of possible side-effects. The more common or serious possible side-effects are listed below:

Amiloride and triamterene

Usually there are no side-effects but they can occur in some people. Possible side-effects include:

• Tummy ache or cramp.

• Dry mouth.

• Feeling dizzy or faint, especially when getting up from sitting or lying positions (due to too low blood pressure).

• Skin rash.

• Feeling sleepy or confused.

• Headache.

• Aches and pains.

• Muscle cramps.

• Weakness.

• Diarrhoea or constipation.

• Potassium levels going too high (hyperkalaemia).

Spironolactone and eplerenone

Possible side-effects include:

• Tummy upsets.

• Feeling sick (nausea) or being sick (vomiting).

• Sexual problems.

• Enlargement of the breasts (both in men and women).

• Irregular menstrual periods.

• Confusion.

• Dizziness.

• Skin rash.

• Excessive hair growth.

• Liver problems.

• Potassium levels going too high.

Who cannot take potassium-sparing diuretics?

There are very few people who are not able to take these medicines. They should not be taken by anyone who has high levels of potassium in their blood, severe kidney problems, or Addison's disease.

In addition, potassium supplements should not be taken with these medicines. Some salt substitutes that you can buy are high in potassium. These should be avoided if you take a potassium-sparing diuretic.

Taking a potassium-sparing diuretic at the same time as an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin receptor antagonist medicine (eg, valsartan, losartan) can also cause very high blood potassium levels.