mexiletine hydrochloride at a glance
Medicine class
Sodium-channel blocker; class Ib antiarrhythmic pharmacology
Licensed role
Symptomatic treatment of myotonia in eligible children, adolescents and adults with non-dystrophic myotonic disorders
How it is taken
Swallow the capsule whole with water while sitting or standing
Key safety requirement
Specialist cardiac assessment and electrolyte checks are required before treatment, with continued monitoring
What is mexiletine hydrochloride used for?
The selected Namuscla product is licensed for:
Reducing symptoms of myotonia in children aged 6 to 11 years who weigh at least 20 kg, adolescents and adults with non-dystrophic myotonic disorders.
How does mexiletine hydrochloride work?
Mexiletine preferentially blocks sodium channels in repeatedly firing muscle fibres. This reduces excessive electrical activity, helping muscles relax more normally after contraction and easing stiffness.
mexiletine hydrochloride preparations and strengths
Capsule
Route: Oral
Strengths: 50 mg, 83 mg, 100 mg, 167 mg, 200 mg
How to take mexiletine hydrochloride
Follow the specialist’s prescription and product leaflet.
Swallow capsules whole with water while sitting or standing; avoid taking them while lying down.
Food does not materially alter absorption, but taking a capsule during a meal may reduce digestive discomfort.
Opening capsules or giving their contents through a feeding tube has not been established as safe or effective. Discuss swallowing difficulties with the clinical team.
mexiletine hydrochloride side effects
Common or expected effects
- Abdominal pain or nausea
- Difficulty sleeping or sleepiness
- Vertigo, headache or tingling sensations
- Blurred vision
- Flushing or low blood pressure
- Tiredness, weakness or limb pain
- Acne
Get urgent medical advice
- A new or worsening abnormal heart rhythm, particularly with chest pain, breathlessness, dizziness or fainting
- Severe blistering, peeling or mucosal rash
- Rash with fever, facial swelling or swollen glands, which may indicate DRESS
- Seizures, collapse or severe confusion
- Symptoms suggesting liver injury, such as jaundice
mexiletine hydrochloride in pregnancy
Information from pregnancy exposure is limited, and mexiletine crosses the placenta. The product information advises avoiding it during pregnancy as a precaution; pregnancy planning or a positive pregnancy test should prompt timely specialist review rather than stopping treatment without advice.
mexiletine hydrochloride while breastfeeding
Mexiletine passes into breast milk, and evidence about effects on breastfed infants is insufficient. A specialist should weigh the benefits of treatment and breastfeeding and agree whether either should be paused or changed; prescribed treatment should not be stopped without review.
mexiletine hydrochloride interactions
Check all prescribed, pharmacy and herbal products before starting them with mexiletine. Important interactions include:
Antiarrhythmics that can cause torsades de pointes
Medicines such as amiodarone, sotalol, quinidine, flecainide and propafenone can increase the risk of a potentially fatal rhythm disturbance and are contraindicated.
Other antiarrhythmics and medicines affecting cardiac conduction
Beta-blockers, verapamil, diltiazem, lidocaine and related medicines may increase cardiac adverse effects and generally require avoidance or exceptional specialist oversight.
Ciprofloxacin, fluvoxamine and other CYP1A2 or CYP2D6 inhibitors
These may raise mexiletine exposure, increasing adverse-effect risk and the need for clinical and ECG review.
Common questions about mexiletine hydrochloride
Answers are fully visible for fast scanning and source review.
What is mexiletine hydrochloride used for in myotonia?
It reduces delayed muscle relaxation and stiffness in non-dystrophic myotonic disorders by calming excessive electrical activity in muscle fibres.
Can children take mexiletine hydrochloride for myotonia?
The selected Namuscla product is licensed for eligible children from 6 years who weigh at least 20 kg, as well as adolescents and adults. Treatment requires specialist oversight.
Why are heart tests needed before mexiletine hydrochloride?
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.