A thiazide water tablet for blood pressure and fluid
Cyclopenthiazide
A water tablet from the thiazide group used to treat high blood pressure and fluid retention.
What is Cyclopenthiazide?
Cyclopenthiazide is a 'water tablet', or diuretic, from the thiazide group. It is used to treat high blood pressure and to remove excess fluid from the body, for example in some heart, kidney or liver conditions that cause swelling. It works on the kidneys to help the body pass more water and salt in the urine, which lowers blood pressure and reduces fluid build-up. It is taken by mouth, usually in the morning so it does not disturb sleep. It can affect the body's salts, such as potassium and sodium, so blood tests are used to keep an eye on these.
Education and reference only. This is a plain-language guide to Cyclopenthiazide — 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
Cyclopenthiazide is a diuretic, commonly called a water tablet, from the thiazide group of medicines. It is used to treat high blood pressure and to help with fluid retention, where excess fluid builds up in the body and causes swelling, which can happen in some heart, kidney or liver conditions. It works on the kidneys to increase the amount of water and salt passed in the urine. It is an older, long-established medicine taken by mouth, usually once in the morning, and is used under medical guidance with occasional blood tests.
How it works
Cyclopenthiazide acts on the kidneys, reducing how much salt (sodium) and water they reabsorb back into the body. As a result, more salt and water are passed out in the urine, which lowers the volume of fluid in the blood vessels and reduces fluid build-up in the tissues. Over time this helps lower blood pressure and ease swelling. Because it changes how the kidneys handle salts, it can lower levels of potassium and sodium and affect other salts, which is why blood tests are used to check the balance, especially when treatment first starts.
Company & origin
Originated / developed by: Generic (long-established).
An older water tablet used in the UK for high blood pressure and for fluid retention, taken by mouth.
What it treats
Conditions Cyclopenthiazide is used for
Practical use
How to take Cyclopenthiazide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take the tablet by mouth in the morning, so the extra urine it produces does not disturb your sleep.
- Attend your blood tests, which check your kidney function and the balance of salts such as potassium and sodium.
- Tell your prescriber if you feel weak, get muscle cramps or feel unusually tired, as these can be signs of low potassium.
- Be careful not to become dehydrated, particularly in hot weather or if you are vomiting or have diarrhoea.
- Tell your prescriber about other medicines, including anti-inflammatory painkillers and other blood-pressure tablets.
Weighing it up
Advantages & disadvantages of Cyclopenthiazide
Advantages
- An effective, long-established treatment for high blood pressure.
- Helps remove excess fluid and ease swelling in some heart, kidney or liver conditions.
- Taken by mouth as a simple once-daily tablet.
Disadvantages
- Can lower the body's salts, particularly potassium, so blood tests are needed.
- Can affect blood sugar, uric acid and cholesterol, which may matter in diabetes or gout.
- Increases how much you need to pass urine, so it is best taken in the morning.
Practical use
Good to know
A practical tip is to take cyclopenthiazide in the morning, because it makes you pass more urine and an evening dose could mean getting up in the night. Because it changes the body's salts, it can lower potassium, which may cause symptoms such as muscle weakness or cramps, so blood tests are used to check this and sometimes a potassium supplement or a different combination is needed. It can also affect blood sugar, uric acid (which can trigger gout) and cholesterol, so these may be reviewed, particularly in people with diabetes or gout. It is sensible not to become dehydrated, especially in hot weather or if you are unwell with vomiting or diarrhoea. Tell your prescriber about other medicines, as some, such as certain blood-pressure medicines and anti-inflammatory painkillers, interact with it.
Who should not take it / use with caution
- People who have had a serious allergic reaction to cyclopenthiazide or similar thiazide medicines should not take it.
- It is avoided in people with severe kidney or liver problems, or with certain salt imbalances, under medical guidance.
- It is used with caution in people with gout or diabetes, and in pregnancy and breastfeeding it is generally avoided, guided by your prescriber.
Monitoring
- Blood tests to check kidney function and the balance of salts such as potassium and sodium.
- Checking blood pressure to see how well it is working.
- Reviewing blood sugar and uric acid where relevant, particularly in people with diabetes or gout.
Side effects
- Passing more urine, especially when treatment first starts.
- Low levels of body salts such as potassium or sodium, which can cause weakness, cramps or tiredness.
- Less commonly, a rise in blood sugar or uric acid (which can trigger gout), or feeling dizzy on standing.
Key interactions
- Anti-inflammatory painkillers can reduce how well it works and affect the kidneys, so use them with care.
- It is often combined with other blood-pressure medicines, which can add to a drop in blood pressure.
- Medicines affected by potassium levels, such as some heart medicines, need monitoring, so tell your prescriber what you take.
Available as: Tablets taken by mouth.
Answers
Cyclopenthiazide: frequently asked questions
What is cyclopenthiazide used for?
It is a water tablet used to treat high blood pressure and to remove excess fluid that causes swelling in some heart, kidney or liver conditions.
Why should I take it in the morning?
It makes you pass more urine, so taking it in the morning means it is less likely to disturb your sleep by making you get up in the night.
Why do I need blood tests?
It changes how the kidneys handle salts and can lower potassium and sodium, so blood tests check the balance and your kidney function, especially early on.
Can it affect gout or diabetes?
Yes, it can raise uric acid, which may trigger gout, and can affect blood sugar, so these may be reviewed if you have gout or diabetes.
What if I feel weak or get cramps?
Muscle weakness, cramps or unusual tiredness can be signs of low potassium, so tell your prescriber, who can check your blood and adjust treatment if needed.
Authoritative sources
- BNF
- NICE CKS
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