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Study Comparing the Safety and Effectiveness of Mexiletine PR and Mexiletine IR for Adults with Non-Dystrophic Myotonias

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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 a group of muscle disorders known as Non-Dystrophic Myotonias. These conditions cause muscle stiffness and difficulty relaxing muscles after use. The study will compare two forms of a medication called Mexiletine, which is used to treat these symptoms. The two forms being compared are Mexiletine PR (prolonged-release) and Mexiletine IR (immediate-release). The goal is to understand how safe and effective these medications are for treating muscle stiffness in adults with non-dystrophic myotonias, which include specific types like myotonia congenita, paramyotonia congenita, and sodium channel myotonia.

Participants in the study will receive either Mexiletine PR or Mexiletine IR over a period of 24 weeks. The study is designed as an open-label, randomized, cross-over trial, meaning that participants will switch between the two forms of the medication during the study. This approach helps researchers compare the effects of each medication form directly. The study will monitor the occurrence of any side effects and how well participants tolerate the medications. Additionally, the study will assess improvements in muscle stiffness and overall quality of life using various tests and questionnaires.

The primary focus is on the safety of the medications, looking at any adverse events that may occur during the treatment period. Secondary measures include video recordings of hand movements, quality of life assessments, and other tests to evaluate the impact of the medications on daily activities. The study aims to provide valuable information on the best treatment approach for managing symptoms in individuals with non-dystrophic myotonias.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Introduction to the study

    The study is designed to compare the safety and effectiveness of two forms of mexiletine for treating symptoms of non-dystrophic myotonias, which include conditions like myotonia congenita, paramyotonia congenita, and sodium channel myotonia.

    Participants must have a confirmed diagnosis of one of these conditions and meet specific health criteria to be eligible.

  2. Step 2

    Medication administration

    Participants will receive mexiletine in two forms: prolonged-release (PR) and immediate-release (IR).

    The medications are administered orally, with dosages including 167 mg, 333 mg, and 500 mg for the prolonged-release form, and 167 mg for the immediate-release form.

    The duration of treatment with each form is 12 weeks.

  3. Step 3

    Monitoring and assessments

    Throughout the study, participants will be monitored for any adverse effects related to the medication.

    Assessments will include video recordings of hand opening time, quality of life questionnaires, and various scales to measure myotonia symptoms and overall health.

  4. Step 4

    Completion of the study

    The study is expected to conclude by April 30, 2026.

    Upon completion, data will be analyzed to determine the safety and effectiveness of the two forms of mexiletine.

Who can join the trial?

7 criteria

  • Have a confirmed diagnosis of non-dystrophic myotonias, which includes conditions like myotonia congenita (MC), paramyotonia congenita (PC), and sodium channel myotonia (SCM).
  • Be a male or a non-pregnant female who is 16 years or older at the time of screening.
  • Have a Body Mass Index (BMI) between 18.5 and 30, and weigh at least 45 kilograms. BMI is a measure that uses your height and weight to work out if your weight is healthy.
  • If you are a female who can have children, you must use a highly effective form of birth control during the study and for at least 7 days after the last dose of the study drug.
  • Have no significant heart problems, as determined by a heart specialist's assessment.
  • Have myotonic symptoms that are severe enough to need treatment.
  • Show signs of handgrip myotonia during screening, which means a delay of 3 seconds or more in relaxing your grip after squeezing your hand as hard as you can. This will be checked using a test called VHOT.

Who cannot join the trial?

3 criteria

  • Patients who are not adults cannot participate. This means only individuals who are 18 years or older can join.
  • Patients who do not have a diagnosis of Non-Dystrophic Myotonias (NDM) cannot participate. This includes specific types like myotonia congenita (MC), paramyotonia congenita (PC), and sodium channel myotonia (SCM).
  • Patients who are part of a vulnerable population may not be eligible. A vulnerable population includes groups that might need special protection, like those with certain disabilities or conditions.
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Investigated drugs

  • Mexiletine PR

    is a medication used in this study to help manage symptoms of myotonia, which is a condition that causes muscle stiffness. This version of mexiletine is designed to release the medication slowly over time, which may help maintain a more consistent level of the drug in the body and potentially reduce side effects.

  • Mexiletine IR

    is another form of the same medication used to treat myotonia. Unlike the PR version, this immediate-release form is designed to release the medication quickly into the body. This study aims to compare the safety and effectiveness of this form with the slow-release version in treating muscle stiffness in patients with non-dystrophic myotonias.

What is already known about the treatment

  • Mexiletine PR

    This medication is administered orally in a prolonged-release form. It is currently being studied in clinical trials for its effectiveness and safety in treating non-dystrophic myotonias, a group of muscle disorders. The main therapeutic indication is to alleviate symptoms of myotonia, which is characterized by muscle stiffness. Mexiletine works by blocking sodium channels in muscle cells, which helps to reduce abnormal muscle contractions. It is classified as a sodium channel blocker.

  • Mexiletine IR

    This medication is also taken orally but in an immediate-release form. It is being compared to the prolonged-release version in clinical trials to assess its safety and efficacy for non-dystrophic myotonias. The primary use is to manage symptoms of myotonia, such as muscle stiffness. Mexiletine IR functions by inhibiting sodium channels in muscle cells, thereby decreasing excessive muscle activity. It belongs to the pharmacological class of sodium channel blockers.

Investigated diseases

Non-Dystrophic Myotonias – Non-dystrophic myotonias are a group of rare muscle disorders characterized by delayed relaxation of muscles after voluntary contraction. This condition leads to stiffness and difficulty in muscle movement, which can be triggered by sudden movements or changes in temperature. The symptoms can vary in severity and may affect different muscle groups, often causing discomfort and impacting daily activities. The condition is caused by genetic mutations affecting ion channels in muscle cells, leading to abnormal muscle excitability. It includes specific types such as myotonia congenita, paramyotonia congenita, and sodium channel myotonia, each with distinct genetic and clinical features. These disorders are typically present from childhood or adolescence and can persist throughout life.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-514970-27-00Protocol codeMEX-NDM-301Estimated enrolment24 patientsSponsorLupin Atlantis Holdings SA

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