A loop 'water tablet' for people who cannot take furosemide
Ethacrynic acid
A strong 'water tablet' that helps the body lose excess fluid and salt, used when furosemide is not suitable.
What is Ethacrynic acid?
Ethacrynic acid is a powerful loop diuretic, or 'water tablet', that helps the body get rid of excess fluid and salt through the urine. It is used less often than furosemide and is mainly reserved for people who cannot take the usual loop diuretics, for example because of a sulfonamide allergy, since unlike most of them it is not a sulfonamide. Its main concerns are strong fluid and salt loss leading to dehydration, and damage to hearing (ototoxicity), which is more likely at high doses or alongside other medicines that affect the ears. It needs careful monitoring of fluids, salts and kidney function.
Education and reference only. This is a plain-language guide to Ethacrynic acid — 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
Ethacrynic acid is an older, powerful 'water tablet' belonging to the loop diuretic family, the same broad group as furosemide. It makes the kidneys pass out more salt and water, which reduces fluid build-up in conditions such as heart failure. Today it is something of a specialist or back-up medicine, used mainly when someone cannot take the more common loop diuretics, particularly people with an allergy to sulfonamide medicines, because ethacrynic acid is not a sulfonamide. It is taken by mouth, or sometimes given by injection in hospital, under close supervision.
How it works
Ethacrynic acid works on a specific part of the kidney called the loop of Henle, where it blocks the reabsorption of salt back into the body. Because more salt stays in the urine, more water follows it out, so the body loses excess fluid. This eases the swelling and breathlessness caused by fluid overload. Because it is a strong diuretic that acts quickly and powerfully, it can shift a lot of fluid and salt in a short time, which is helpful but also why dehydration and salt imbalances are a real risk and why monitoring matters.
Company & origin
Originated / developed by: Generic (specialist supply).
An older, powerful loop diuretic used in the UK mainly when someone cannot take furosemide, such as people with a sulfonamide allergy.
What it treats
Conditions Ethacrynic acid is used for
Practical use
How to take Ethacrynic acid
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth as prescribed, usually earlier in the day so you are not woken at night needing to pass urine.
- Keep to the dose and timing you are given, as it is a strong diuretic that can shift a lot of fluid quickly.
- Report any ringing in the ears, dizziness or change in hearing straight away, as it can affect hearing.
- Watch for signs of too much fluid loss, such as feeling very thirsty, lightheaded, weak or dizzy on standing.
- Attend your blood tests so that your salts and kidney function can be checked while you take it.
Weighing it up
Advantages & disadvantages of Ethacrynic acid
Advantages
- A powerful way to remove excess fluid and ease swelling and breathlessness.
- A useful alternative for people who cannot take furosemide, such as those with a sulfonamide allergy.
- Works quickly to shift fluid, which can give noticeable relief.
Disadvantages
- Can cause strong fluid and salt loss, leading to dehydration and low salt levels.
- Can damage hearing (ototoxicity), especially at high doses or with other ear-affecting medicines.
- An older, less commonly used medicine that needs careful monitoring and specialist input.
Practical use
Good to know
The most important thing to understand about ethacrynic acid is that it is reserved for specific situations: it is a strong loop diuretic kept mainly for people who cannot take furosemide or similar, such as those with a sulfonamide allergy. Because it is so powerful, it can cause too much fluid and salt loss, leading to dehydration, dizziness on standing, and low levels of salts such as potassium and sodium, so blood tests and how you feel are watched closely. A particularly important and somewhat distinctive risk is damage to hearing (ototoxicity), which can cause ringing in the ears, hearing loss or, rarely, permanent damage; this is more likely with high doses, rapid injection, kidney problems, or when combined with other medicines that can harm the ears, such as certain antibiotics. Report any change in hearing straight away. Taking it earlier in the day helps avoid disturbed sleep from needing to pass urine.
Who should not take it / use with caution
- People who have had a serious allergic reaction to ethacrynic acid should not take it.
- It is used with great care, or avoided, in people who are already very dehydrated or have very low salt levels.
- It is used with particular caution alongside other medicines that can harm hearing, such as certain antibiotics.
- It is used cautiously in people with significant kidney or liver problems, under specialist guidance.
Monitoring
- Regular blood tests for salts such as potassium and sodium, and for kidney function.
- Watching weight, fluid balance, blood pressure and signs of dehydration.
- Checking for any change in hearing, especially with higher doses or other ear-affecting medicines.
Side effects
- Passing a lot of urine, thirst, dizziness and lightheadedness, especially on standing.
- Low levels of salts such as potassium, sodium and magnesium, found on blood tests.
- Ringing in the ears or hearing changes, which can rarely be permanent and need urgent attention.
- Stomach upset, and rarely more serious effects, which should be reported to your prescriber.
Key interactions
- Other medicines that can harm hearing, such as aminoglycoside antibiotics, raise the risk of hearing damage.
- Medicines and conditions that lower potassium add to the risk, which matters with drugs like digoxin.
- It can affect blood pressure and kidney medicines, so tell your prescriber everything you take.
Available as: Tablets taken by mouth, and a form for injection used in hospital.
Answers
Ethacrynic acid: frequently asked questions
What is ethacrynic acid used for?
It is a powerful 'water tablet' (loop diuretic) used to remove excess fluid in conditions such as heart failure, mainly when someone cannot take furosemide.
Why might I be given this instead of furosemide?
Ethacrynic acid is not a sulfonamide, so it can be an option for people with a sulfonamide allergy who cannot take the usual loop diuretics.
Can it affect my hearing?
Yes, it can cause ringing in the ears or hearing loss, especially at high doses or with other ear-affecting medicines, so report any hearing change straight away.
Why do I need blood tests?
Because it shifts a lot of fluid and salt, it can lower salts such as potassium and affect the kidneys, so blood tests keep these in check.
When should I take it?
Usually earlier in the day, so that needing to pass extra urine does not disturb your sleep at night.
The wider class
About Loop diuretic (water tablet)
Ethacrynic acid belongs to the loop diuretic (water tablet) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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