An older heart-rhythm medicine, now uncommon
Quinidine
An older medicine for abnormal heart rhythms, now used only rarely and under specialist supervision.
What is Quinidine?
Quinidine is an older medicine used to control certain abnormal heart rhythms. It is related to quinine and is now used only rarely, because newer treatments are usually safer and easier to manage. Its most important risk is that it can affect the heart's electrical rhythm and cause a dangerous fast rhythm called torsades, so it needs heart tracing (ECG) monitoring. It can also cause a cluster of effects known as cinchonism, such as ringing in the ears, headache and visual changes, as well as a fall in the blood cells that help clotting, and it interacts with many other medicines.
Education and reference only. This is a plain-language guide to Quinidine — 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
Quinidine is one of the oldest heart-rhythm medicines, chemically related to quinine, the antimalarial. It works on the electrical signals in the heart to help control abnormal rhythms. Once used quite widely, it is now an uncommon, specialist-only choice in the UK because newer antiarrhythmic medicines are generally safer and need less intensive monitoring. When it is used, it is started and supervised by a heart specialist, often in hospital, with close attention to the heart's rhythm and to blood tests, because it can have a number of important and potentially serious effects.
How it works
Quinidine slows and steadies the electrical signals that pass through the heart muscle, which can help bring an abnormal rhythm back to normal or stop it returning. The same action that helps the rhythm can also, in some people, disturb the heart's electrical recovery and lengthen part of the heart tracing known as the QT interval. If the QT becomes too long, it raises the risk of a dangerous fast rhythm called torsades de pointes. This is why treatment is started carefully, with heart tracing (ECG) checks, and why it is reserved for specialist situations.
Company & origin
Originated / developed by: Generic (long-established).
A long-established medicine, related to quinine, once widely used in the UK for heart-rhythm problems but now used only rarely and under specialist care.
What it treats
Conditions Quinidine is used for
Practical use
How to take Quinidine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it exactly as your heart specialist directs; this is not a medicine to adjust on your own.
- Attend all heart-tracing (ECG) and blood-test appointments, as monitoring is an essential part of treatment.
- Report ringing in the ears, headache, dizziness or changes in your vision promptly, as these can be early warning signs.
- Tell your team about any easy bruising or unusual bleeding, as quinidine can lower platelets.
- Give a full list of all your other medicines, because quinidine interacts with many of them.
Weighing it up
Advantages & disadvantages of Quinidine
Advantages
- Can help control certain abnormal heart rhythms when other options are unsuitable.
- A long-established medicine with decades of clinical experience behind it.
- Still has a place in specific specialist situations under careful supervision.
Disadvantages
- Can lengthen the QT interval and trigger a dangerous heart rhythm called torsades.
- Can cause cinchonism (ringing in the ears, headache, dizziness and visual changes) and lower the platelets that help clotting.
- Interacts with many other medicines and needs close monitoring, which is why it is now used only rarely.
Practical use
Good to know
The most important thing to understand about quinidine is that it is a powerful older medicine with several serious risks, which is why it is now used only rarely and always under specialist supervision. It can lengthen the QT interval on the heart tracing and trigger a dangerous rhythm called torsades, so ECGs are used to watch for this. It can also cause a group of effects called cinchonism, which includes ringing in the ears (tinnitus), headache, dizziness and changes in vision; these are a signal to seek advice. It can lower the platelets that help blood to clot, leading to easy bruising or bleeding, and it interacts with a long list of other medicines, including digoxin and warfarin. Because of all this, never start, stop or change the dose yourself, and report any new symptoms promptly.
Who should not take it / use with caution
- People who have had a serious allergic reaction to quinidine or quinine should not take it.
- It is generally avoided in people with certain heart-rhythm problems, including a naturally long QT interval or certain conduction problems, unless a specialist advises otherwise.
- It is used with great caution, or avoided, in people taking other medicines that affect the heart rhythm, and in those with low platelets.
- It should only ever be used under specialist supervision with regular heart-tracing and blood monitoring.
Monitoring
- Regular heart-tracing (ECG) checks, especially when starting, to watch the QT interval and rhythm.
- Blood tests to check platelets, blood counts and, where relevant, drug levels.
- Watching for cinchonism, bruising or bleeding and any change in heart symptoms.
Side effects
- Cinchonism: ringing in the ears, headache, dizziness and changes in vision.
- Stomach upset such as nausea or diarrhoea.
- A lengthened QT interval and, rarely, a dangerous fast rhythm called torsades de pointes.
- A fall in the platelets that help clotting, causing easy bruising or bleeding, and rarely other serious blood or allergic reactions.
Key interactions
- It raises levels of digoxin, so doses often need adjusting and monitoring.
- It can increase the effect of warfarin and raise the risk of bleeding.
- It should not usually be combined with other medicines that lengthen the QT interval, because the risk of a dangerous rhythm adds up.
Available as: Tablets taken by mouth.
Answers
Quinidine: frequently asked questions
What is quinidine used for?
It is an older medicine used to help control certain abnormal heart rhythms, but it is now used only rarely and always under specialist supervision.
Why is it used so rarely now?
Newer heart-rhythm medicines are generally safer and need less intensive monitoring, and quinidine carries serious risks such as dangerous rhythm changes and effects on the blood.
What is cinchonism?
Cinchonism is a cluster of effects linked to quinidine and quinine, including ringing in the ears, headache, dizziness and changes in vision; report these to your team.
Why do I need heart tracings?
Quinidine can lengthen the QT interval on the heart tracing and, rarely, trigger a dangerous rhythm called torsades, so ECGs are used to watch for this.
Can it affect other medicines I take?
Yes, it interacts with many medicines, including digoxin and warfarin, so always give your team a full list of everything you take.
Authoritative sources
- BNF
- NICE CKS
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