Commonly used drug could transform treatment of rare muscle disorder

Medical Xpress / University College London / The Lancet Neurology ^ | Sept. 27, 2024 | Vinojini Vivekanandam et al

[ConservativeMind]

Lamotrigine, a drug commonly used to treat epilepsy and certain mood disorders, has been shown to be an excellent treatment option for a rare genetic neuromuscular disease known as non-dystrophic myotonia, in a world-first trial.

The study detailed the "head-to-head" trial implemented by the researchers to test two drugs, mexiletine and lamotrigine, on people with the condition.

Patients were randomly assigned to receive either mexiletine for eight weeks followed by lamotrigine for eight weeks, or the reverse order, with a seven-day break in between treatments. Neither the participants nor the researchers knew which treatment was being given at any time.

At the end of the trial, lamotrigine was found to reduce stiffness—the main symptom of non-dystrophic myotonia—by around the same amount as mexiletine.

Non-dystrophic myotonias are life-changing muscle disorders caused by problems with ion channels in the muscles. Symptoms (such as muscle stiffness, pain, weakness, and fatigue) usually start in childhood and can cause significant disability—reducing quality of life and employability. There is currently no cure.

In 2012, the same UCL team led a multi-centered international trial that repurposed mexiletine—a sodium channel blocker—and showed it was effective in treating non-dystrophic myotonia and improving quality of life.

As a result, mexiletine became the first-line treatment for non-dystrophic myotonias world-wide.

However, not all patients respond to the treatment and one third developed significant side-effects, the most common being reflux or gastrointestinal side effects. Additionally, mexiletine can't be prescribed during pregnancy, when myotonia often worsens.

Lamotrigine provides an alternative solution, as the trial showed that the drug was well tolerated by patients, and has additional advantages as it can be used in pregnancy and is cheaper. No serious side effects were reported.

[ConservativeMind]

Lamotrigine goes for $20 a prescription (GoodRX), while mexiletine is nearly double and appears to have more side effects.

Both can now treat non-dystrophic myotonia about the same.

[ConservativeMind]

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