Skip to content
Clinical Trials – home

Rare diseases

Investigational molecules

Locations

Our offerNewsroom

RecruitingRare disease

Long-Term Safety and Efficacy Study of Mexiletine Hydrochloride for Patients with Myotonic Dystrophy Type 1 and Type 2

Fast replyInvestigational
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

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 treatment for people with Myotonic Dystrophy types 1 and 2. Myotonic Dystrophy is a genetic disorder that affects muscle function, causing symptoms like muscle stiffness and weakness. The treatment being tested is called Mexiletine, which is taken as granules for prolonged-release oral suspension. This means the medication is designed to be released slowly in the body over time, helping to manage symptoms more effectively.

The purpose of the study is to evaluate how safe and effective Mexiletine is when used over a long period. Participants in the study will take the medication once daily. The study will monitor any side effects and how well the medication helps with symptoms like muscle stiffness. Participants will also undergo regular health checks, including physical exams and heart monitoring, to ensure their safety throughout the study.

This study is an extension of a previous study, meaning it continues to follow patients who have already been taking Mexiletine to gather more information about its long-term use. The study will last for up to 18 months, during which participants will be regularly assessed to track their progress and any changes in their condition. The goal is to provide valuable insights into the long-term management of Myotonic Dystrophy with Mexiletine.

The research process

The trial runs in 6 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 MEX-DM-302 study. This study is an extension to evaluate the long-term safety and effectiveness of a medication called mexiletine for treating muscle stiffness in myotonic dystrophy types 1 and 2.

  2. Step 2

    Medication administration

    The medication used is mexiletine granules for prolonged-release oral suspension. It is available in doses of 500 mg, 333 mg, and 167 mg.

    The medication is taken once daily by mouth. The exact dosage will be determined by the study team based on individual needs.

  3. Step 3

    Treatment duration

    The treatment period lasts for 26 weeks. During this time, the effects of the medication on muscle stiffness and overall health will be monitored.

  4. Step 4

    Monitoring and assessments

    Regular assessments will be conducted to monitor health and the medication's effects. These include physical exams, laboratory tests, and heart monitoring using an ECG.

    Specific tests include the Handgrip Dynamometer to measure muscle strength, the Myotonia Behavior Scale, and the 10 meter Walk Test to assess mobility.

  5. Step 5

    Safety evaluations

    The study will track any side effects or adverse events that occur during the treatment. This includes monitoring for any heart-related issues using a Holter monitor.

  6. Step 6

    Completion of the study

    At the end of the 26-week period, a final evaluation will be conducted to assess the overall impact of the treatment on muscle stiffness and quality of life.

Who can join the trial?

9 criteria

  • Have a confirmed diagnosis of Myotonic Dystrophy type 1 or type 2 (DM1/DM2) through genetic testing.
  • Be able to understand and agree to sign an informed consent form. If under 18, a parent or legal guardian must sign, and the patient must also agree in writing.
  • Be able to understand what the study involves and plan to stay in the study until the end, which is 26 weeks of treatment.
  • Be a male or a non-pregnant female who is at least 16 years old.
  • Have a Body Mass Index (BMI) between 18.5 and 30, and weigh at least 45 kg. BMI is a measure of body fat based on height and weight.
  • If a female can have children, she 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.
  • Have enough strength in the fingers to hold the handle of a device used to measure muscle stiffness, known as myotonia.
  • For DM1 patients only, have a Muscular Impairment Rating Scale (MIRS) score of 2, 3, or 4. This scale measures the level of muscle weakness.

Who cannot join the trial?

5 criteria

  • Patients who have not completed the MEX-DM-302 study.
  • Patients who do not have a diagnosis of Myotonic Dystrophy type 1 or type 2. Myotonic Dystrophy is a genetic disorder that affects muscle function.
  • Patients who are not within the specified age range for the study.
  • Patients who are not part of the specified clinical trial group.
  • Patients who are considered part of a vulnerable population that the study does not include.
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

We usually reply within a few days

Verified sites

All sites with verified contact details – recruitment status may not be available; ask directly

Trial locations

Where you can join this trial

Countries are shaded by recruitment status. Click a recruiting country to ask about joining there.

Recruiting
Not finding your country?

Not sure what to do next?

Joining a clinical trial can seem overwhelming. We guide you step by step, so you know exactly what to expect and how we support you through the process.

See the full process and FAQ

Investigated drugs

Mexiletine PR is a medication being studied for its long-term safety and effectiveness in treating myotonia, which is a symptom of myotonic dystrophy types 1 and 2. Myotonia causes muscle stiffness and difficulty relaxing muscles after use. This study is focused on patients who have already participated in a previous study, and it aims to see how well the medication works and how safe it is when taken once daily over a longer period.

What is already known about the treatment

Mexiletine PR – This medication is administered orally in a prolonged-release form, designed for once-daily use. It is currently being studied in clinical trials to evaluate its long-term safety and effectiveness for treating myotonia in patients with Myotonic Dystrophy types 1 and 2. Mexiletine PR is primarily indicated for managing symptoms associated with these conditions. At the molecular level, it works by blocking sodium channels in muscle cells, which helps reduce muscle stiffness and spasms. It is classified pharmacologically as a sodium channel blocker.

Investigated diseases

  • Myotonic Dystrophy Type 1

    This is a genetic disorder characterized by progressive muscle wasting and weakness. It often begins in adulthood and can affect various body systems, including the heart, eyes, and endocrine system. Individuals with this condition may experience prolonged muscle contractions, known as myotonia, which can make it difficult to relax muscles after use. Over time, muscle weakness can become more pronounced, affecting mobility and daily activities. The severity and progression of symptoms can vary widely among individuals.

  • Myotonic Dystrophy Type 2

    This is a genetic disorder similar to type 1 but generally has a milder presentation. It also involves muscle weakness and myotonia, but symptoms often appear later in life and progress more slowly. Muscle pain and stiffness are common, and the condition can also affect the heart and other organs. Unlike type 1, facial muscle weakness is less common, and individuals may maintain more muscle strength. The progression of symptoms can vary, with some individuals experiencing only mild effects.

Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-511178-66-00Protocol codeMEX-DM-303Estimated enrolment176 patientsSponsorLupin Atlantis Holdings SA

sourced from the EU Clinical Trials Register and site verification

Want to learn more about this trial or check if you can participate?

Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

ClinicalTrials.eu

Every clinical trial in Europe, in plain language.

Explore the full ecosystem of clinical research in Europe.

Search trials

Legal notice · Published by CTIN POLAND sp. z o.o., ul. rtm. Witolda Pileckiego 67/109, 02-781 Warsaw, Poland · KRS 0001111334 · REGON 528919042 · NIP 9512598637

© 2026 Clinical Trials EU – European Clinical Trials Information Network

GDPR compliance, ISO 9001 and ISO 27001 certified (LL-C Certification)

On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).