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Long-term Safety and Efficacy of Mexiletine for Patients With Skeletal Muscle Channelopathies.

Long-term Safety and Efficacy of Mexiletine for Patients With Skeletal Muscle Channelopathies The skeletal muscle channelopathies include the nondystrophic myotonias and the periodic paralyses. Myotonia is the core clinical feature of the nondystrophic myotonias and may be a feature of hyperkalemic periodic paralysis. It is caused by mutations in the skeletal muscle voltage-gated chloride channel gene CLCN1 or sodium channel gene SCN4A. Adequate treatment of myotonia is important for quality of life, mobility, and functional independence.1 Mexiletine acts on voltage-gated sodium channels. Its most frequent adverse effect is gastrointestinal2,3 but minor neurological effects (eg, tremor) are also reported.4,5 Two randomized clinical trials have demonstrated the efficacy of mexiletine for the short-term treatment of myotonia2,3 but long-term safety and efficacy data outside a trial setting are lacking. We performed a retrospective review of our large skeletal muscle channelopathy patient cohort to address this.