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NAMUSCLA (mexilétine)

Opinions on drugs - Posted on Dec 24 2019

Reason for request

First assessment

  • Key points

Favourable opinion for reimbursement in the symptomatic treatment of myotonia in adult patients with non-dystrophic myotonic disorders.

  • What therapeutic improvement?

Slight therapeutic improvement in the treatment of myotonia in the absence of muscular dystrophy, known as non-dystrophic myotonic disorders.

  • Role in the care pathway?

The treatment of myotonia congenita (MC) (chloride channel genetic defects), in the event of significant functional effects, is symptomatic. In adults, mexiletine is introduced progressively, following a cardiological opinion (proarrhythmic effect). Carbamazepine (TEGRETOL and its generics) and phenytoin (DI-HYDAN), used off-label, are the alternatives in the event of intolerance and/or contraindication. The treatment of paramyotonia congenita (PC) (CNSA1 sodium channel genetic defects) is symptomatic and begins with control of aggravating factors. Mexiletine is prescribed in the same way as for treatment of MC. Some forms of PC are sensitive to acetazolamide (DIAMOX), used off-label, which can be combined with mexiletine. Physiotherapy can be useful in addition to medicinal treatment.

Role of NAMUSCLA in the care pathway:

NAMUSCLA (mexiletine) is a first-line symptomatic treatment for adult patients with non-dystrophic myotonic disorders. A detailed and careful cardiac evaluation (ECG, 24-48-hour Holter-monitoring and echocardiography) should be carried out in all patients in order to determine the cardiac tolerability of mexiletine.

  • Special recommendations

The initiation of treatment with NAMUSCLA (mexiletine) should be performed by a practitioner practising in a neuromuscular disease reference/expert centre.

Clinical Benefit


The clinical benefit of NAMUSCLA (mexiletine) is substantial in the MA indication.


Clinical Added Value



  • The results of 3 clinical trials, i.e., one phase 3 trial and two phase 2 trials, demonstrating a clinical benefit of mexiletine in comparison with placebo, based on a subjective criterion, muscle stiffness, which was the primary outcome measure used in the studies.
  • The exploratory nature of the results concerning objective criteria, such as electrophysiological parameters (compound motor action potential amplitude, time to perform motor sequences (chair test, timed up and go test)), assessed as non-ranked secondary outcome measures.
  • The safety profile that appears to be favourable based on the available data, 


  • the Transparency Committee considers that NAMUSCLA (mexiletine) provides a minor clinical added value (level IV) in the care pathway as a symptomatic treatment of myotonia in adult patients with non-dystrophic myotonic disorders.

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