NICE guidance - mexiletine for treating the symptoms of myotonia in non-dystrophic myotonic disorders

Mexiletine (Namuscla) is recommended, within its marketing authorisation, as an option for treating the symptoms of myotonia in adults with non-dystrophic myotonic disorders (1).

Mexiletine is a class 1b antiarrhythmic medication with a high affinity for muscle sodium channels (2)

In a series of N-of-1 trials of mexiletine vs placebo in patients with nondystrophic myotonia, there was a reduction in mean daily-reported muscle stiffness that was consistent with the treatment effect in a previous randomized clinical trial (3)

• findings support the efficacy of mexiletine for treatment of nondystrophic myotonia as well as the feasibility of N-of-1 trials for assessing interventions in some chronic rare diseases

Reference:

• NICE (December 2021). Mexiletine for treating the symptoms of myotonia in non-dystrophic myotonic disorders
• Statland JM, Bundy BN, Wang Y, et al. Mexiletine for symptoms and signs of myotonia in nondystrophic myotonia: a randomized controlled trial. JAMA. 2012;308(13):1357-1365. doi:10.1001/jama.2012.12607
• Stunnenberg BC, Raaphorst J, Groenewoud HM, et al. Effect of Mexiletine on Muscle Stiffness in Patients With Nondystrophic Myotonia Evaluated Using Aggregated N-of-1 Trials. JAMA. 2018;320(22):2344-2353. doi:10.1001/jama.2018.18020