A medicine for primary periodic paralysis
Dichlorphenamide
A specialist medicine used to reduce attacks of muscle weakness in primary periodic paralysis.
What is Dichlorphenamide?
Dichlorphenamide is a specialist medicine used to reduce attacks of muscle weakness in primary periodic paralysis, a rare inherited condition in which the muscles become weak or temporarily paralysed. It is a carbonic anhydrase inhibitor, related to acetazolamide, and is taken by mouth. Its most common side effects include tingling or pins and needles (paraesthesia), a low blood potassium level and a build-up of acid in the body (metabolic acidosis); it can also cause kidney stones, falls and effects on thinking. It is related to sulfonamides, so it is used with care in people with sulfonamide allergy, and treatment is monitored with blood tests.
Education and reference only. This is a plain-language guide to Dichlorphenamide — 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
Dichlorphenamide is a specialist medicine used to reduce how often and how severely attacks happen in primary periodic paralysis, a rare inherited muscle disorder. In this condition, people have episodes in which their muscles become very weak or temporarily paralysed, often linked to changes in the body's salts (electrolytes). Dichlorphenamide is a carbonic anhydrase inhibitor, the same family as acetazolamide, and is taken by mouth. It is prescribed and supervised by a specialist team and is used to help keep attacks under better control over time.
How it works
Dichlorphenamide blocks an enzyme called carbonic anhydrase, which is involved in handling salts and acid balance in the body, particularly in the kidneys. By doing so, it changes the balance of certain salts and makes the body slightly more acidic, which is thought to stabilise the muscle cells so they are less likely to misfire and cause an attack of weakness. The same actions that help the muscles also explain its main side effects, such as tingling, a low potassium level and a build-up of acid, which is why blood tests are used to keep an eye on the body's salts during treatment.
Company & origin
Originated / developed by: Specialist manufacturer.
A specialist medicine used in the UK to reduce attacks of muscle weakness in primary periodic paralysis, a rare inherited muscle condition.
Practical use
How to take Dichlorphenamide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth exactly as advised, and keep to the schedule you are given.
- Drink enough fluid, as this helps reduce the risk of kidney stones.
- Take care with driving, using machinery and getting up quickly until you know whether it affects your balance or thinking.
- Tell your prescriber if you have ever had a reaction to a sulfonamide ('sulfa') medicine.
- Attend your blood tests so your team can check your potassium and acid levels.
Weighing it up
Advantages & disadvantages of Dichlorphenamide
Advantages
- Can reduce how often and how severely attacks of weakness happen in primary periodic paralysis.
- Taken by mouth as tablets.
- A targeted option for a rare condition with few alternatives.
Disadvantages
- Commonly causes tingling, a low potassium level and a build-up of acid in the body.
- Can cause kidney stones, dizziness, confusion and an increased risk of falls.
- Related to sulfonamides, so it must be used with care in people with sulfonamide allergy, and needs blood-test monitoring.
Practical use
Good to know
Several practical points matter with dichlorphenamide. Tingling or pins and needles, especially in the hands, feet and around the mouth, is common and often settles. Because it changes the body's salts and acid balance, it can lower potassium and cause a build-up of acid (metabolic acidosis), so blood tests are used to monitor these. It can increase the risk of kidney stones, so drinking enough fluid is usually advised, and it can cause dizziness, confusion or problems with thinking and balance that may lead to falls, so take care until you know how it affects you. It is chemically related to sulfonamides ('sulfa' medicines), so tell your prescriber if you have ever reacted to a sulfonamide. As with similar medicines, it is started carefully and reviewed regularly to balance benefit against side effects.
Who should not take it / use with caution
- People who have had a serious allergic reaction to dichlorphenamide should not take it.
- It is used with caution, or avoided, in people who have reacted to sulfonamide ('sulfa') medicines.
- It is used with care in people with significant liver or kidney problems, or a tendency to kidney stones.
- It is used with caution in people prone to low potassium or to disturbances of the body's salts.
Monitoring
- Regular blood tests to check potassium and the body's acid (bicarbonate) balance.
- Watching for tingling, dizziness, confusion, falls and signs of kidney stones.
- Reviewing how well attacks are controlled against the side effects of treatment.
Side effects
- Tingling or pins and needles (paraesthesia), often in the hands, feet and around the mouth.
- A low blood potassium level and a build-up of acid in the body (metabolic acidosis).
- Kidney stones, dizziness, confusion or problems with thinking and balance, which can lead to falls.
- Rarely, serious skin reactions or blood problems linked to sulfonamide-type medicines, which need urgent attention.
Key interactions
- It can add to the effects of other medicines that lower potassium, such as some water tablets (diuretics).
- It can interact with high-dose aspirin and with other carbonic anhydrase inhibitors, so tell your team what you take.
- It can change how some other medicines behave because it alters the body's acid balance, so a full medicines list is important.
Available as: Tablets taken by mouth.
Answers
Dichlorphenamide: frequently asked questions
What is dichlorphenamide used for?
It is a specialist medicine used to reduce attacks of muscle weakness in primary periodic paralysis, a rare inherited muscle condition.
Why do I get tingling on it?
Tingling or pins and needles, often in the hands, feet and around the mouth, is a common effect of this type of medicine and often settles over time.
Why are my blood tests checked?
It can lower potassium and cause a build-up of acid in the body, so blood tests are used to monitor these and keep treatment safe.
Does it cause kidney stones?
It can increase the risk of kidney stones, so drinking enough fluid is usually advised; tell your team about any back pain or blood in your urine.
I am allergic to sulfa medicines, can I take it?
Dichlorphenamide is related to sulfonamides, so tell your prescriber about any sulfonamide allergy, as it may not be suitable or may need extra caution.
The wider class
About Carbonic anhydrase inhibitor (periodic paralysis)
Dichlorphenamide belongs to the carbonic anhydrase inhibitor (periodic paralysis) 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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