Namuscla
Authorised
This medicine is authorised for use in the European Union
Mexiletine
MedicineHumanAuthorised
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- Application under evaluation
- CHMP opinion
- European Commission decision
Overview
Namuscla is a medicine used to treat symptoms of myotonia (muscle stiffness) in children aged 6 to 11 years weighing at least 20 kg, adolescents aged 12 to 17 years and adults with non-dystrophic myotonic disorders, a group of inherited muscle disorders. Non-dystrophic means no muscle wasting occurs in patients affected by the condition.
Patients with non-dystrophic myotonic disorders experience muscle stiffness and pain because their muscles are slow to relax after contraction.
Myotonic disorders are rare, and Namuscla was designated an ‘orphan medicine’ (a medicine used in rare diseases) on 19 November 2014. Further information on the orphan designation can be found on the EMA website.
Namuscla can only be obtained with a prescription and is available as capsules to be taken by mouth. In adults, the dose depends on the intensity of the symptoms and how the patient responds to treatment. In children the dose depends on their bodyweight. Patients should have tests to check how well their heart is working both before beginning and regularly throughout treatment.
For more information about using Namuscla, see the package leaflet or contact your doctor or pharmacist.
The active substance in Namuscla, mexiletine, works by blocking channels in muscle cells that allow sodium ions (electrically charged particles) to pass in and out. These sodium channels play a role in the contraction and relaxation of muscles and are hyperactive in patients with myotonic disorders, causing excessive contractions and stiffness. By blocking them, the medicine helps to reduce the stiffness that occurs when the contractions are prolonged.
Because it has a similar effect on the heart muscle, mexiletine has been authorised in the EU for many years for use in patients with abnormal heart rhythm.
In a study involving 25 patients with non-dystrophic myotonia, Namuscla was shown to be more effective than placebo (a dummy treatment) at reducing muscle stiffness.
Muscle stiffness was self-assessed by each patient before and after treatment and scored on a scale running from 0 to 100 (most severe). After 18 days of treatment, the average score for patients treated with Namuscla decreased from 66 to 24, while the score for patients given placebo went from 75 to 66.
The company also provided supportive data from the literature on the effectiveness of Namuscla.
A second study involved 12 children aged between 6 to 17 years with non-dystrophic myotonia, all of whom received Namuscla. After 8 weeks of treatment, all children showed an improvement in their scores for stiffness, pain, and fatigue. In this study, Namuscla was not compared with placebo or another treatment.
Studies carried out with Namuscla are described in more detail in the medicine’s assessment reports.
For the full list of side effects and restrictions with Namuscla, see the package leaflet.
The most common side effects with Namuscla (which may affect more than 1 in 10 people) include abdominal (belly) pain, vertigo and insomnia (difficulty sleeping).
Some side effects can be serious. Among the serious side effects, the most frequent (which may affect up to 1 in 10,000 people) include arrhythmias (disturbances of heart rhythm) and a severe reaction affecting skin, blood and internal organs, known as drug reaction with eosinophilia and systemic symptoms (DRESS).
Namuscla must not be used in patients who are hypersensitive (allergic) to the active substance, mexiletine, to any other ingredients of the medicine or to local anaesthetics (medicines that block out sensation used to prevent pain in a part of the body). Namuscla must also not be used in patients with various heart problems or together with certain medicines.
Namuscla was shown to be effective at easing the symptoms of myotonia in adults and children from 6 years of age with non-dystrophic myotonic disorders, thus improving their quality of life. The safety profile of Namuscla is well known and its side effects affecting the heart are considered to be manageable with restrictions in use and monitoring during treatment.
The European Medicines Agency therefore decided that Namuscla’s benefits are greater than its risks and it can be authorised for use in the EU.
The company that markets Namuscla will provide educational material for doctors and a patient alert card with important information about the risks associated with the medicine, in particular the risk of arrhythmias.
Recommendations and precautions to be followed by healthcare professionals and patients for the safe and effective use of Namuscla have also been included in the summary of product characteristics and the package leaflet.
As for all medicines, data on the use of Namuscla are continuously monitored. Side effects reported with Namuscla are carefully evaluated and any necessary action taken to protect patients.
Namuscla received a marketing authorisation valid throughout the EU on 18 December 2018.
Product information
Latest procedure affecting product information:X/0000258210
28/05/2026
This medicine’s product information is available in all official EU languages.
Select 'available languages' to access the language you need.
Product information documents contain:
- summary of product characteristics (annex I);
- manufacturing authorisation holder responsible for batch release (annex IIA);
- conditions of the marketing authorisation (annex IIB);
- labelling (annex IIIA);
- package leaflet (annex IIIB).
Product details
- Name of medicine
- Namuscla
- Active substance
- Mexiletine hydrochloride
- International non-proprietary name (INN) or common name
- Mexiletine
- Therapeutic area (MeSH)
- Myotonic Disorders
- Anatomical therapeutic chemical (ATC) code
- C01BB02
Pharmacotherapeutic group
Cardiac therapyTherapeutic indication
Namuscla is indicated for the symptomatic treatment of myotonia in adult patients with non-dystrophic myotonic disorders.
News on Namuscla
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