An old long-acting diabetes tablet
Chlorpropamide
An old, very long-acting diabetes tablet that lowers blood sugar; now largely obsolete.
What is Chlorpropamide?
Chlorpropamide is an older diabetes tablet from the first generation of sulfonylureas, once used to lower blood sugar in type 2 diabetes. It works by prompting the pancreas to release more insulin. Its defining problem is that it is very long-acting, so it can cause prolonged low blood sugar (hypoglycaemia) that lasts a long time and can be dangerous, especially in older people and those with reduced kidney function. It can also cause low sodium in the blood and a flushing reaction if alcohol is taken with it. Because of these risks it is now largely obsolete and has been replaced by safer medicines.
Education and reference only. This is a plain-language guide to Chlorpropamide — 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
Chlorpropamide is a medicine from the sulfonylurea group, which lower blood sugar in type 2 diabetes by encouraging the body to make more of its own insulin. It is one of the first-generation, older sulfonylureas and is notable for being very long-acting, staying in the body far longer than newer alternatives. It was once a common diabetes tablet, but its long duration of action makes low blood sugar harder to manage and longer-lasting, and it has other distinctive side effects. For these reasons it is now considered obsolete and has been replaced by shorter-acting, safer diabetes treatments. Any use is historical and would be under careful medical supervision.
How it works
Chlorpropamide works by stimulating the beta cells in the pancreas to release more insulin, the hormone that moves sugar out of the blood and into the body's cells. By increasing insulin output, it lowers the level of glucose in the blood. The problem is that it is very long-acting, so its insulin-releasing effect continues for a long time after each dose. This means that if blood sugar drops too low, the low level can persist for many hours or even longer, which is the main reason it is regarded as more dangerous than newer, shorter-acting medicines, particularly in older people or those whose kidneys clear it more slowly.
Company & origin
Originated / developed by: Generic (no longer routinely used).
An older, very long-acting diabetes tablet from the first generation of sulfonylureas, once used to lower blood sugar in type 2 diabetes.
What it treats
Conditions Chlorpropamide is used for
Practical use
How to take Chlorpropamide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it exactly as prescribed, usually once a day, and keep your eating pattern regular to avoid low blood sugar.
- Learn the signs of low blood sugar, such as shakiness, sweating, hunger or confusion, and how to treat them.
- Be aware that low blood sugar from this medicine can last a long time, so seek help even after it seems to improve.
- Avoid alcohol or use it with great care, as it can cause flushing and add to the risk of low blood sugar.
- Tell your prescriber about kidney problems, as these make low blood sugar more likely and longer-lasting.
Weighing it up
Advantages & disadvantages of Chlorpropamide
Advantages
- Lowers blood sugar in type 2 diabetes by helping the body release more of its own insulin.
- Taken as a once-daily tablet.
- A long-established medicine with decades of experience behind it.
Disadvantages
- Very long-acting, so low blood sugar can be prolonged and dangerous, especially in older people and kidney impairment.
- Can cause low sodium in the blood and a flushing reaction with alcohol.
- Now largely obsolete, replaced by safer, shorter-acting diabetes medicines.
Practical use
Good to know
The most important thing to understand about chlorpropamide is its very long action, which makes low blood sugar (hypoglycaemia) a real danger: because the medicine lingers, an episode of low blood sugar can last a long time and come back, so it can be especially serious in older people and in anyone with reduced kidney function. It can also cause the blood sodium level to fall (a condition linked to a problem called SIADH), which can cause confusion, tiredness or feeling unwell. Another characteristic effect is a flushing reaction, with warmth and redness of the face, if alcohol is taken while on it. Because of these risks, and because better-tolerated diabetes medicines are now available, it is largely obsolete and rarely used. Anyone who has taken it should know the signs of low blood sugar and how to treat them.
Who should not take it / use with caution
- People who have had a serious allergic reaction to chlorpropamide or other sulfonylureas should not take it.
- It is unsuitable for people with significant kidney impairment because of the risk of prolonged low blood sugar.
- It is generally avoided in older people, who are especially vulnerable to long-lasting low blood sugar.
- It is not used in type 1 diabetes, where insulin is needed.
Monitoring
- Regular checks of blood sugar control and watching for low blood sugar.
- Checking the blood sodium level, as it can fall on this medicine.
- Reviewing kidney function, since reduced kidney function increases the risk of prolonged low blood sugar.
Side effects
- Low blood sugar (hypoglycaemia), which can be prolonged and severe because the medicine is long-acting.
- Low sodium in the blood (linked to SIADH), which can cause confusion, tiredness or feeling unwell.
- A flushing reaction, with warmth and redness of the face, when alcohol is taken.
- Weight gain and, less commonly, stomach upset or skin reactions.
Key interactions
- Alcohol can cause a flushing reaction and add to the risk of low blood sugar.
- Other medicines that lower blood sugar, including insulin, can increase the risk of hypoglycaemia.
- Some medicines and conditions affecting the kidneys can make low blood sugar more likely and longer-lasting.
Available as: Tablets taken by mouth.
Answers
Chlorpropamide: frequently asked questions
What is chlorpropamide used for?
It is an older sulfonylurea tablet once used to lower blood sugar in type 2 diabetes by helping the pancreas release more insulin.
Why is its long action a problem?
Because it stays in the body a long time, any low blood sugar it causes can be prolonged and dangerous, especially in older people and those with reduced kidney function.
Can I drink alcohol with it?
Alcohol can cause a flushing reaction, with warmth and redness of the face, and can add to the risk of low blood sugar, so it is best avoided or used with great care.
Why is it rarely used now?
Its very long action, risk of prolonged low blood sugar, low sodium and alcohol-flush reaction mean it is largely obsolete and has been replaced by safer diabetes medicines.
What is the low-sodium problem it can cause?
It can lower the blood sodium level, linked to a condition called SIADH, which may cause confusion, tiredness or feeling unwell and is checked with blood tests.
The wider class
About Sulfonylurea (first-generation, long-acting)
Chlorpropamide belongs to the sulfonylurea (first-generation, long-acting) 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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