A potassium-sparing diuretic (water tablet)
Triamterene
A potassium-sparing diuretic, often combined with a thiazide, that removes excess fluid while helping to keep potassium up.
What is Triamterene?
Triamterene is a potassium-sparing water tablet (diuretic). It helps the body remove excess fluid and salt while, unlike many other water tablets, holding on to potassium rather than losing it. It is often combined with a thiazide diuretic, which on its own tends to lower potassium, so the two balance each other. The main thing to watch is that potassium can rise too high, especially in people with kidney problems or those also taking an ACE inhibitor or ARB. A harmless quirk is that it can give urine a slightly bluish tinge.
Education and reference only. This is a plain-language guide to Triamterene — 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
Triamterene is a type of water tablet, or diuretic, known as potassium-sparing. Diuretics help the body get rid of extra fluid and salt, which can be useful for conditions such as fluid build-up and, as part of treatment, raised blood pressure. What makes triamterene different from many diuretics is that it tends to keep potassium in the body rather than flush it out. For this reason it is often combined with a thiazide diuretic, which lowers potassium, so that together they remove fluid while keeping potassium more balanced. It is taken by mouth.
How it works
Triamterene acts on the kidneys, where it changes how salt (sodium) and potassium are handled. It helps the kidneys pass out more sodium and water, which reduces fluid build-up, but at the same time it reduces the amount of potassium lost in the urine, so potassium is spared. Many other diuretics, including thiazides, do the opposite with potassium and tend to lower it, which is why triamterene is often paired with a thiazide so their effects on potassium offset each other. Because of this potassium-sparing action, the key thing to watch for is potassium rising too high.
Company & origin
Originated / developed by: Various manufacturers.
A potassium-sparing diuretic used in the UK, often combined with a thiazide diuretic, to remove excess fluid while protecting potassium.
Practical use
How to take Triamterene
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth as prescribed, often in the morning so increased urination does not disturb your sleep.
- Attend your blood tests so your potassium and kidney function can be checked.
- Avoid potassium supplements and potassium-based salt substitutes unless your prescriber advises otherwise.
- Tell your prescriber if you take an ACE inhibitor or ARB, as these also raise potassium.
- Do not be alarmed if your urine looks slightly bluish; this is a harmless effect.
Weighing it up
Advantages & disadvantages of Triamterene
Advantages
- Removes excess fluid while helping to keep potassium up, unlike many water tablets.
- Pairs well with a thiazide diuretic, balancing each other's effect on potassium.
- Taken by mouth and well established in practice.
Disadvantages
- Can raise blood potassium too high, especially with kidney problems or certain other medicines.
- Causes more frequent urination, which is why it is usually taken in the morning.
- Needs blood tests to monitor potassium and kidney function.
Practical use
Good to know
The dominant safety point is potassium: because triamterene spares potassium, the main risk is that potassium in the blood rises too high (hyperkalaemia), which can affect the heart. This risk is greater in people with kidney problems and in those also taking medicines that raise potassium, such as ACE inhibitors, ARBs or potassium supplements, so blood tests are used to keep an eye on potassium and kidney function. A harmless and sometimes surprising effect is that triamterene can give urine a faint bluish colour, which is nothing to worry about. It is taken by mouth, often in the morning so that the extra trips to the toilet do not disturb sleep, and it is best to avoid potassium-rich salt substitutes unless your prescriber advises otherwise.
Who should not take it / use with caution
- People with high blood potassium or significant kidney problems should generally not take it.
- It is used with caution, or avoided, alongside other medicines that raise potassium, such as ACE inhibitors, ARBs or potassium supplements.
- It is used with care in pregnancy and in people with certain liver problems, on medical advice.
Monitoring
- Regular blood tests for potassium and kidney function.
- Checking blood pressure and fluid status as relevant to why it is being used.
- Reviewing other medicines that may also affect potassium.
Side effects
- A rise in blood potassium, which is checked with blood tests.
- More frequent urination, especially soon after starting.
- Nausea, stomach upset, dizziness or dry mouth in some people.
- A harmless bluish tinge to the urine.
Key interactions
- ACE inhibitors, ARBs and potassium supplements add to the risk of high potassium.
- Potassium-based salt substitutes can also push potassium too high.
- Anti-inflammatory painkillers (NSAIDs) can affect the kidneys and potassium when combined.
Available as: Tablets and capsules taken by mouth, including combinations with a thiazide diuretic.
Answers
Triamterene: frequently asked questions
What is triamterene used for?
It is a potassium-sparing water tablet that removes excess fluid while helping to keep potassium up, often combined with a thiazide diuretic.
Why does it spare potassium?
It acts on the kidneys to remove sodium and water while reducing the loss of potassium, so potassium is held on to rather than flushed out.
Why are my potassium levels checked?
Because it spares potassium, blood potassium can rise too high, especially with kidney problems or medicines like ACE inhibitors, so it is monitored with blood tests.
Why has my urine turned a bit blue?
Triamterene can give urine a faint bluish colour; this is a harmless effect and nothing to worry about.
When should I take it?
It is usually taken in the morning so that the extra trips to the toilet do not disturb your sleep.
Authoritative sources
- BNF
- NICE CKS
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