A potassium-sparing water tablet
Amiloride
A mild, potassium-sparing water tablet, often combined with a thiazide diuretic.
What is Amiloride?
Amiloride is a mild "water tablet" (diuretic) that helps the body get rid of extra fluid and salt, used in high blood pressure and in conditions causing fluid build-up such as heart failure. What makes it different from most water tablets is that it keeps potassium in the body rather than losing it, which is why it is called potassium-sparing. Because of this, there is a risk of potassium rising too high, so care is needed with ACE inhibitors, ARBs and potassium supplements. It is often combined with a thiazide water tablet to balance potassium levels.
Education and reference only. This is a plain-language guide to Amiloride — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Amiloride is a potassium-sparing diuretic, a type of water tablet. Like other water tablets it helps the body pass extra fluid and salt as urine, which can lower blood pressure and ease fluid build-up in conditions such as heart failure. Unlike most water tablets, which make the body lose potassium, amiloride helps the body hold on to potassium. It is taken by mouth as a tablet, often combined with a thiazide diuretic (a combination called co-amilozide) so that the two balance each other's effect on potassium.
How it works
Amiloride acts on the kidneys to increase the amount of salt and water passed as urine, while reducing the amount of potassium lost. Removing extra fluid lowers blood pressure and relieves the swelling and congestion of fluid build-up. Because most other water tablets, such as thiazides, cause potassium to fall, amiloride is often paired with them so that one tablet's potassium loss is offset by the other's potassium retention, keeping levels in balance.
Company & origin
Originated / developed by: Generic (long-established).
A long-established water tablet used in the UK, often combined with another diuretic, that helps the body lose fluid while keeping potassium.
What it treats
Conditions Amiloride is used for
Practical use
How to take Amiloride
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it in the morning, as it increases how much urine you pass and can disturb sleep if taken late.
- Take it regularly as prescribed, with or after food if it upsets your stomach.
- Avoid potassium supplements and potassium-containing salt substitutes unless your prescriber advises them.
- Tell your prescriber you take it before starting an ACE inhibitor, an ARB or other medicines, as potassium can rise.
- Keep your blood-test appointments, which check your potassium and kidney function.
- Report muscle weakness, an irregular heartbeat or feeling generally unwell, which can be signs of high potassium.
Weighing it up
Advantages & disadvantages of Amiloride
Advantages
- Helps remove excess fluid while keeping potassium, rather than causing it to fall.
- Balances the potassium loss of thiazide and loop water tablets when combined with them.
- A long-established, well-understood medicine for blood pressure and fluid build-up.
Disadvantages
- Can cause potassium to rise too high, which can be dangerous, so blood tests are needed.
- Needs particular care with ACE inhibitors, ARBs and potassium supplements.
- On its own it is only a mild water tablet, so it is often combined with another.
Practical use
Good to know
The defining feature of amiloride is that it is potassium-sparing: it helps the body keep potassium rather than lose it. This is useful for balancing other water tablets, but it also means potassium can rise too high, which can be dangerous for the heart. Because of this, particular care is needed if it is combined with ACE inhibitors, ARBs (sartans), potassium supplements or salt substitutes that contain potassium, and blood tests are used to keep an eye on potassium and kidney function. It is a fairly mild diuretic on its own, which is why it is often given with a thiazide. As with other water tablets, it is usually taken in the morning to avoid passing urine at night.
Who should not take it / use with caution
- People with high blood potassium, or conditions that raise it, should not take it.
- It is avoided in people with severe kidney problems, where potassium can build up dangerously.
- Used with great care, or avoided, alongside other medicines that raise potassium unless closely monitored.
Monitoring
- Blood tests for potassium and kidney function, especially when starting or changing other medicines.
- Blood pressure checks to confirm control.
- Reviewing for signs of high potassium, such as muscle weakness or an irregular heartbeat.
Side effects
- High blood potassium, which may cause muscle weakness or an irregular heartbeat and is checked by blood tests.
- Passing more urine, feeling thirsty, and sometimes a dry mouth.
- Nausea, stomach upset, dizziness or feeling faint on standing.
Key interactions
- Combined with ACE inhibitors, ARBs or potassium supplements, it can raise potassium to dangerous levels.
- Potassium-containing salt substitutes can add to the rise in potassium.
- Anti-inflammatory painkillers and some other medicines can affect the kidneys and potassium, so tell your prescriber what you take.
Available as: Tablets taken by mouth, including combined tablets with a thiazide (co-amilozide).
Answers
Amiloride: frequently asked questions
How is amiloride different from other water tablets?
Most water tablets make the body lose potassium, but amiloride is potassium-sparing, meaning it helps the body keep potassium rather than lose it.
Why is high potassium a concern?
Too much potassium in the blood can affect the heart and cause an irregular heartbeat, which is why blood tests are used to check it.
Can I take potassium supplements with it?
Usually not, because amiloride already keeps potassium in the body, so adding supplements or potassium salt substitutes can push levels too high; ask your prescriber.
Why is it combined with another water tablet?
On its own it is mild and keeps potassium, while thiazides are stronger but lose potassium, so combining them balances the effect on potassium.
When should I take it?
It is usually taken in the morning, as it makes you pass more urine and could disturb your sleep if taken later in the day.
Authoritative sources
- BNF
- NICE CKS
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