Clinical Efficacy Trial of Mexiletine for Myotonic Dystrophy Type 1

A Randomized, Placebo Controlled, Clinical Efficacy Trial of Mexiletine for Myotonic Dystrophy Type-1 (DM1)

The purpose of this study is to investigate the effects of mexiletine treatment for 6 months on ambulation, myotonia, muscle function and strength, pain, gastrointestinal functioning, cardiac conduction, and quality of life in myotonic dystrophy type 1 (DM1).

This study will provide data on the long term (6 months) safety and efficacy of mexiletine in:

• improving the distance participants are able to walk in six minutes;
• reducing myotonia;
• improving muscle strength;
• increasing lean muscle mass;
• decreasing musculoskeletal pain;
• improving gastrointestinal function and swallowing);
• improving functional abilities;
• decreasing cardiac arrhythmias; and
• improving disease-specific health related quality-of-life.

Inclusion Criteria:

• A diagnosis of DM1, confirmed by DM1 genetic mutation
• Ability to walk 30 feet (assistance with cane and/or leg bracing permitted)
• Presence of grip myotonia

Exclusion Criteria:

• Congenital DM1
• Treatment with Mexiletine within past 8 weeks
• Second or third degree heart block, atrial flutter, atrial fibrillation, ventricular arrhythmias, or is receiving medication for treatment of a cardiac arrhythmia
• Receiving another antimyotonia drug
• Liver or kidney disease requiring ongoing treatment
• Has a seizure disorder
• Is pregnant or lactating
• Had severe depression within 3 months or a history of suicide ideation
• Has any one of the following medical conditions: uncontrolled diabetes mellitus, congestive heart failure, symptomatic cardiomyopathy, symptomatic coronary artery disease, cancer (other than skin cancer) less than five years previously, multiple sclerosis, or other serious medical illness.
• Drug or alcohol abuse within 3 months
• Coexistence of another neuromuscular disease
• Is unable to give informed consent
• Severe arthritis or other medical condition (besides DM1) that would significantly impact ambulation