Mexiletine Safe, Helpful for MMD-Related Myotonia

Results showing that the drug mexiletine can safely and effectively combat myotonia, the troublesome inability to relax muscles at will that occurs in myotonic dystrophy (MMD), were announced at an October 2005 meeting of the International Myotonic Dystrophy Consortium in Quebec.

Richard Moxley, a neurologist at the Sen. Paul D. Wellstone Muscular Dystrophy Cooperative Research Center at the University of Rochester (N.Y.), studied people with MMD1 who had difficulty relaxing their grip at will. In two studies, each of which lasted seven weeks and had 20 participants, Moxley's group found that either 150 or 200 milligrams of mexiletine three times a day was effective.

They suggest more studies to see whether the drug can combat weakness or muscle pain.

Cardiologists at the meeting voiced concern about whether mexiletine, which is usually prescribed to slow nerve impulses in the heart, could cause or exacerbate heartbeat irregularities in patients with MMD. The investigators reported that they saw no changes in electrocardiograms (which examine heart rhythm) during the studies.