An oral medicine for heart-rhythm problems and myotonia
Mexiletine
An oral medicine used to steady abnormal heart rhythms and to ease the muscle stiffness of myotonia.
What is Mexiletine?
Mexiletine is a medicine taken by mouth that calms over-excitable electrical activity. It has two main uses: steadying certain abnormal heart rhythms, and easing the muscle stiffness (myotonia) seen in conditions such as myotonic disorders, where muscles are slow to relax. It is taken with food to reduce stomach upset. Like other heart-rhythm medicines, it can sometimes worsen or trigger rhythm problems, so it is started and supervised carefully, especially in people with certain heart conditions such as heart block. Common side effects include tremor, stomach upset and dizziness.
Education and reference only. This is a plain-language guide to Mexiletine — 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
Mexiletine is a medicine that works on the tiny electrical signals in heart muscle and other muscles. It has long been used to help control certain abnormal heart rhythms, and it is also used to reduce myotonia, the prolonged muscle stiffness where muscles are slow to relax after being used, which occurs in some inherited muscle conditions. It is taken by mouth as a capsule, usually with food. Because it affects the heart, it is started carefully and supervised by a specialist, particularly a heart or neuromuscular team, depending on what it is being used for.
How it works
Muscle and heart cells fire using channels that let sodium move in and out, creating electrical signals. Mexiletine partly blocks these sodium channels, calming over-excitable or repetitive electrical activity. In the heart, this can steady certain abnormal rhythms; in myotonia, it helps muscles relax more normally after they have contracted, easing stiffness. Because it acts on the heart's electrical system, the same action that helps can occasionally upset the rhythm, which is why it is introduced carefully and the heart is checked.
Company & origin
Originated / developed by: Specialist manufacturer.
An older medicine used in the UK to steady the heart's rhythm and, more recently, to ease the muscle stiffness of myotonia.
Practical use
How to take Mexiletine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth with food, which helps reduce stomach upset.
- Take it at evenly spaced times each day as prescribed, and do not change the dose yourself.
- Tell your prescriber about any palpitations, fainting or dizziness, as these can relate to heart rhythm.
- Give a full list of your other medicines, as mexiletine interacts with several of them.
- Attend any heart tracing checks your team arranges, especially when starting or changing the dose.
Weighing it up
Advantages & disadvantages of Mexiletine
Advantages
- Can steady certain abnormal heart rhythms and ease the muscle stiffness of myotonia.
- Taken by mouth as a capsule rather than needing injections.
- A long-established medicine with decades of experience behind its use.
Disadvantages
- Like other rhythm medicines, it can sometimes worsen or trigger heart-rhythm problems.
- Commonly causes stomach upset, so it must be taken with food, along with tremor and dizziness.
- Needs careful supervision and is used with caution in certain heart conditions such as heart block.
Practical use
Good to know
A key safety point with mexiletine, as with all heart-rhythm medicines, is that it can sometimes make rhythm problems worse or trigger new ones, so it is started carefully, often with heart tracing checks, and is used with caution in people with certain heart conditions such as heart block or a slow heart rate. Taking it with food is important because it commonly upsets the stomach, and food can reduce nausea. Other common effects include a fine tremor, dizziness, and a feeling of unsteadiness. It interacts with several other medicines, including some other heart and rhythm medicines, so a full medicines list matters. Whether it is being used for the heart or for myotonia, regular review helps make sure it is both working and being tolerated.
Who should not take it / use with caution
- People who have had a serious allergic reaction to mexiletine should not take it.
- It is generally avoided in people with certain heart-conduction problems, such as heart block, unless they have a pacemaker.
- It is used with caution after a recent heart attack and in people with certain other heart conditions.
- It is used with care, and under specialist guidance, in pregnancy.
Monitoring
- Heart tracing checks, especially when starting or changing the dose.
- Reviewing symptoms such as palpitations, dizziness or fainting.
- Checking that it is easing rhythm problems or myotonia and is being tolerated.
Side effects
- Stomach upset, nausea or heartburn, which is why it is taken with food.
- A fine tremor, dizziness or unsteadiness.
- Tiredness, headache or, in some people, a sense of confusion.
- Less commonly but importantly, worsening or new heart-rhythm problems, which need urgent review.
Key interactions
- It interacts with several other heart and rhythm medicines, so these are reviewed together.
- Medicines that change how the liver handles it can raise or lower its levels and effects.
- Give a full medicines list, including over-the-counter products, to your prescriber.
Available as: Capsules taken by mouth.
Answers
Mexiletine: frequently asked questions
What is mexiletine used for?
It is used to steady certain abnormal heart rhythms and to ease the muscle stiffness (myotonia) seen in some inherited muscle conditions, where muscles are slow to relax.
Why must I take it with food?
Mexiletine commonly upsets the stomach, so taking it with food helps reduce nausea and heartburn.
Can it affect my heart rhythm?
Yes. Like other rhythm medicines, it can occasionally worsen or trigger rhythm problems, so it is started carefully and your heart may be checked with tracings.
Why does my hand shake on it?
A fine tremor is a common side effect of mexiletine; tell your prescriber if it is troublesome, as the dose may be reviewed.
Does it interact with other medicines?
Yes. It interacts with several medicines, including some other heart and rhythm medicines, so give your prescriber a full list of everything you take.
Authoritative sources
- BNF
- NICE CKS
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