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Study on Long-term Safety and Efficacy of Mexiletine for Children with Myotonic Disorders

Verified siteRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying the long-term safety and effectiveness of a medication called Mexiletine in children with certain muscle disorders known as myotonic disorders. These disorders include nondystrophic myotonias and myotonic dystrophies, which can cause muscle stiffness and difficulty relaxing muscles after use. The study involves children who have already participated in previous studies and tolerated the medication well.

The treatment being tested includes different doses of Mexiletine in the form of hard capsules, specifically Mexiletine 62 mg, Mexiletine 83 mg, and Namuscla 167 mg. The purpose of the study is to gather more information about how safe and effective Mexiletine is for treating symptoms of muscle stiffness in children over a longer period. Participants will take the medication by mouth and will be monitored regularly to check for any side effects and to see how well the medication is working in reducing muscle stiffness.

Throughout the study, the children will have their muscle stiffness assessed using simple scales and tests. These assessments will help determine any changes in their condition over time. The study will also look at the overall quality of life of the participants and any changes in their health. The goal is to ensure that Mexiletine is a safe and effective treatment option for children with these muscle disorders.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Joining the study

    Participation begins after completing the initial study MEX-NM-301 and tolerating the medication mexiletine.

    Assent from the patient and consent from a parent or guardian are required.

  2. Step 2

    Medication administration

    The medication mexiletine is administered in the form of hard capsules.

    Dosages include Mexiletine 62 mg, Mexiletine 83 mg, and Namuscla 167 mg.

    The medication is taken orally.

  3. Step 3

    Monitoring and assessments

    Adverse events are monitored throughout the study.

    Every 3 months, changes in muscle stiffness are assessed using a Visual Analogue Scale (VAS) or Faces score.

    Every 6 months, handgrip myotonia is measured using a grip dynamometer.

  4. Step 4

    Additional evaluations

    Every 3 months, changes in vital signs and clinical laboratory values are recorded.

    Every 6 months, clinical myotonia assessments are conducted, including tests for eyelid myotonia and flexor myotonia.

    Quality of life is evaluated using the Paediatric Quality of Life (PedsQL) score.

  5. Step 5

    Study duration

    The study is estimated to conclude by June 13, 2026.

Who can join the trial?

4 criteria

  • The patient must have completed a previous study called MEX-NM-301 and tolerated the medication **Mexiletine** during that study.
  • The patient must be able and willing to agree to participate in the study, and a parent or legal guardian must be willing to sign a written consent form before the study begins.
  • The patient must continue to meet the requirements of the previous study, MEX-NM-301.
  • The study is open to both male and female patients.
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Investigated drugs

Mexiletine is a medication being studied for its long-term safety and effectiveness in treating myotonia, a condition that affects muscle relaxation, in children. This study is an extension of previous research, aiming to gather more information on how well mexiletine works and how safe it is for young patients who have already participated in earlier trials.

What is already known about the treatment

Mexiletine – Mexiletine is administered orally in the form of capsules. It is currently being studied in clinical trials to assess its long-term safety and efficacy for treating myotonic disorders, specifically nondystrophic myotonias and myotonic dystrophies in pediatric patients. The main therapeutic indication for mexiletine is the symptomatic treatment of myotonia, which involves muscle stiffness. At the molecular level, mexiletine works by blocking sodium channels in muscle cells, which helps to reduce the excessive electrical activity that causes muscle stiffness. It is classified pharmacologically as a sodium channel blocker.

Investigated diseases

Myotonic Disorders – Myotonic disorders are a group of conditions characterized by prolonged muscle contractions, known as myotonia, which can cause stiffness and difficulty in relaxing muscles after use. These disorders include nondystrophic myotonias and myotonic dystrophies, such as type 1 and type 2. Nondystrophic myotonias are typically caused by genetic mutations affecting ion channels in muscle cells, leading to abnormal muscle excitability. Myotonic dystrophies, on the other hand, are progressive conditions that not only affect muscles but can also impact other systems in the body, such as the heart and eyes. Symptoms often begin in childhood or early adulthood and can vary widely in severity. Over time, individuals may experience increasing muscle weakness and stiffness, impacting daily activities.
Trial detailsLast updated 7 Oct 2026
Age0-17PhasePhase IIITrial ID2024-513484-89-00Protocol codeMEX-NM-303Estimated enrolment12 patientsSponsorLupin Europe GmbH

sourced from the EU Clinical Trials Register and site verification

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