Due to insufficient good quality data and lack of randomised studies, it is impossible to determine whether drug treatment is safe and effective in the treatment of myotonia. Larger, well-designed randomised controlled trials are needed to assess the efficacy and tolerability of drug treatment for myotonia.
Treatment of myotonia with antiarrhythmic drugs.
The effects of disopyramide, phenytoin, mexiletine, and tocainide were compared in 30 patients with myotonic disorders. The severity of myotonia was assessed by clinical and electromyographic criteria at the end of each treatment phase lasting four weeks. Mexiletine (MXT) and tocainide (TCD) were found to be the most potent antimyotonic agents. The antimyotonic efficacy of MXT and TCD is explained by their fast-blocking effect on voltage-dependent sodium channels in the muscle membrane. The benefits of myotonia control with pharmacological agents must be weight against the risk of therapy in the individual patient. Because of the risks of hematologic problems, TCD is not recommended by us for the treatment of myotonia.