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Long-term Mexiletine Use Was Safe and Effective in Patients with Myotonic Dystrophy 1 and 2

Mexiletine was safe and effective for long-term use in patients with both myotonic dystrophy types 1 and 2, according to a retrospective study published online on March 24 in Neurology: Clinical Practice.

Mexiletine is an oral medication that blocks voltage-gated sodium channels in cardiac myocytes and nerve cells. It has mainly been used to suppress ventricular arrhythmias.

Myotonic dystrophy types 1 and 2, which are inherited in an autosomal dominant manor, share clinical features such as myotonic myopathy, cataract, and cardiac conduction abnormalities.

In the current study, 96 percent of the study participants reported some improvement in myotonia symptoms with mexiletine therapy, such as cataract and myotonic myopathy. There were no clinically meaningful cardiac adverse events as a result of long-term use of the drug, reported Christina Mousele, MD, of the University College London, and colleagues.  

The results still highlight the importance of the need for collaborative monitoring and evaluation with cardiology as a common clinical feature of the condition is cardiac conduction abnormalities, the researchers noted.

“These findings support that mexiletine is a beneficial and relatively well-tolerated treatment other than gastrointestinal side-effects. This may be mediated by slow dose titration and co-prescription of dyspeptic therapy where indicated," they wrote.

Prior research has focused on the short-term use of myotonic dystrophy. The studies have shown that mexiletine was both safe and effective in non-dystrophic myotonia and myotonic dystrophy, but the research only focused long-term use for non-dystrophic myotonia, the study authors noted.

Dr. Mousele and colleagues evaluated 20 patients with DM1 and five with DM2 over an average period of 32.9 months.

The clinicians administered mexiletine using a standard dose titration of 50 to 100 mg per week until the patient was given a total of 600 mg of mexiletine or until the symptoms went away.

The researchers assessed efficacy on the basis of subjective patient reports as documented by the clinician—as ineffective, partially effective, and effective.  Patients for whom the drug was effective had total resolution of myotonic symptoms; those experiencing partial effectiveness had some improvements but not total resolution of their myotonic symptoms, and individuals for whom the prescription was ineffective experienced no difference in their myotonic symptoms before or during therapy.

Mexiletine was effective in lowering the severity, duration, and/or frequency of myotonia in 21 patients, partially effective for three, and ineffective for one.

Some limitations of the study include the small cohort size, its retrospective nature, lack of information on prescription drug adherence, and that the control or placebo group were not blinded, the researchers noted.


Dr. Mousele did not report any disclosures.​

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Mousele C, Matthews E, Pitceathly R, et al. Long-term safety and efficacy of mexiletine in myotonic dystrophy types 1 and types 2. Neurol Clin Prac 2021; Epub 2021 Mar 24.