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Myotonic DystrophyPhase 3NCT06523400

The Efficacy and Safety of Once Daily Mexiletine PR in Patients With Myotonic Dystrophy Type 1 and Type 2

A Phase 3 study testing Mexiletine granules for prolonged-release oral suspension in people with Myotonic Dystrophy, run by Lupin Ltd. at 7 sites in 6 countries.

Recruiting

Looking for participants now. Contact the study team or a site below to ask about taking part.

Sites and contacts
Official record
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Trial summary

A Randomized, Double-blind, Placebo-Controlled, Multi-Center Study to Investigate the Efficacy and Safety of Once Daily Mexiletine PR During 26 Weeks of Treatment in Patients with Myotonic Dystrophy Type 1 and Type 2 (HERCULES study) Study website: https://myotonicdystrophystudy.com/ Read more about this study

Who is it for?
Ages 16 years and older
Conditions the study is for
Myotonic Dystrophy
What is being tested?
Mexiletine granules for prolonged-release oral suspension
Type of treatment
Pill or oral medicine
Could I receive a placebo?
Yes, some participants may receive a placebo
How many people
176 participants
Where
7 sitesin 6 countries
Study dates
13 Feb 2025to Jun 2027
Phase
Phase 3
Are there results?
Not yet: the study is under way

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 16 years and older
  • All sexes
  • No healthy volunteers
  • Child, Adult, Older adult

Who may be able to join

  • DM1 or DM2 diagnosis confirmed genetically;
  • Ability to comprehend and willingness to sign an informed consent (ICF) or ICF of the parent(s)/legal guardian and written assent from the patient (if patient < 18 years of age);
  • Ability to understand the study requirements including intention to stay in the study until the end-of-study visit at 26 weeks of treatment;
  • Male or non-pregnant female ≥16 years of age;
  • Body Mass Index (BMI) of 18.5 kg/m2 to 30 kg/m2, and weight ≥45 kg;
  • Female patients of childbearing potential must be using a highly effective form of birth control for the duration of the study and for at least 7 days after last dose of study drug;
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  • No significant cardiac abnormalities as determined by a cardiologist's assessment;
  • Have sufficient finger flexor strength to grasp the handle of the dynamometer used to measure myotonia;
  • Presence of clinical handgrip myotonia (delayed relaxation of grip of ≥ 3 seconds after maximum voluntary contraction) at screening using VHOT;
  • Be able to walk independently 10 meters (cane, walker, orthoses allowed);
  • DM1 patients only - Muscular impairment rating scale (MIRS) score of 2, 3 or 4.-

Who cannot join

  • Are pregnant or lactating;
  • Have any one of the following medical conditions: uncontrolled diabetes mellitus, cancer other than skin cancer less than five years previously (e.g., basal-cell carcinoma (BCC) and squamous-cell carcinoma (SCC) of skin allowed), multiple sclerosis, seizure disorders, or other serious medical illness;
  • Severe renal impairment (glomerular filtration rate (GFR) < 30 mL/min);
  • Medical conditions which could interfere with muscle function such as infections, trauma, fractures, or planned surgery;
  • Medical conditions that could affect hand functioning including but not limited to rheumatoid arthritis, Dupuytren's contracture, hand deformity, etc.;
  • Severe arthritis or medical condition (other thanDM1/DM2) that would significantly impact ambulation;
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  • High incidence of falls or fall-associated fractures (>5 falls during the past 12 months);
  • Preexisting elevated liver function tests > 3 times the upper limit of normal (ULN) at screening (alanine transaminase (ALT)/aspartate transaminase (AST), gamma-glutamyl transferase (GGT)) and/or any abnormal chemistry, hematology or urine lab considered clinically significant by investigator;
  • Serum potassium values < 3.5 mmol/L or > 5.0 mmol/L or serum magnesium values < 1.7 mg/dL. Electrolytic imbalance such as hypokalaemia, hyperkalaemia or hypomagnesaemia may increase the proarrhythmic effects of mexiletine. Electrolyte imbalances need to be corrected before administering mexiletine and will be monitored throughout treatment.
  • Treatment with mexiletine within 4 weeks prior to baseline (Day 1);
  • Intake of any anti-myotonic treatment within 4 weeks prior to baseline (Day 1) or 5 half-lives, whichever is longer such as metformin, such as propafenone, flecainide, lamotrigine, carbamazepine or any other channel-blocker/ anticonvulsive drugs;
  • Use of any concomitant medications that could increase the cardiac risk;
  • Known allergy to mexiletine or any local anesthetics;
  • Participation in another interventional clinical study during the last 3 months or 5 half-lives of the investigational medicinal product, whichever is longer;
  • Wheelchair-bound or bed-ridden;
  • Any cardiac safety associated condition including any of the following criteria detected by screening cardiac evaluations including 24-hr Holter monitor, echocardiogram and clinical evaluations:
  • PR interval ≥240 ms or QRS duration ≥120 ms on resting ECG
  • Personal history of 3rd degree or 2nd degree type 2 atrioventricular block or sinus node dysfunction with pauses ≥3 seconds, complete bundle branch block, bifascicular and trifascicular block or any heart block susceptible to evolve to complete heart block
  • Personal history of sustained atrial fibrillation, flutter or tachycardia (duration >30 seconds)
  • Personal history of non-sustained (ventricular triplets or more) or sustained ventricular tachycardia
  • Myocardial infarction (acute or past) or coronary artery stenosis >50%, presence of abnormal Q waves
  • New York Heart Association (NYHA) Class II to IV heart failure
  • Left ventricular systolic dysfunction with ejection fraction <50%
  • Sinus node dysfunction (including ECG sinus rate <50 beats per minute (BPM))
  • Co-administration of antiarrhythmics inducing torsades de pointes (class Ia: quinidine, procainamide, disopyramide, ajmaline; class Ic: encainide, flecainide, propafenone, moricizine; class III: amiodarone, sotalol, ibutilide, dofetilide, dronedarone, vernakalant)
  • Co-administration of other classes of antiarrhythmics (class Ib: lidocaine, phenytoin, tocainide; class II: propranolol, esmolol, timolol, metoprolol, atenolol, carvedilol, bisoprolol, nebivolol; class IV: verapamil, diltiazem)
  • Patients with implantable cardioverter defibrillators (ICDs) and pacemakers are excluded
  • Presence of symptomatic coronary artery disease

Trial locations and contacts

7 sites in 6 countries. Contact the study team or a site near you to ask about taking part.

7 sites in 6 countries

United Kingdom2 sites, 2 recruiting
  • Saint George's University Hospitals NHS Foundation Trust

    London

    neurogenetics@stgeorges.nhs.uk

    Recruiting
  • University College Hospital

    London

    Recruiting

Other trials in United Kingdom

Belgium1 site, 1 recruiting
  • Laboratory for Muscle Diseases and Neuropathies

    Leuven

    Recruiting

Other trials in Belgium

Denmark1 site, 1 recruiting
  • Aarhus University Hospital

    Aarhus

    Recruiting

Other trials in Denmark

Germany1 site, 1 recruiting
  • Ludug-Maximilians University

    München

    Recruiting

Other trials in Germany

Italy1 site, 1 recruiting
  • Azienda Ospedaliera Universitaria Policlinico Tor Vergata

    Rome

    Recruiting

Other trials in Italy

Spain1 site, 1 recruiting
  • University Hospital of Madrid

    Madrid

    Recruiting

Other trials in Spain

About this study

Official title: A Randomized, Double-Blind, Placebo-Controlled, Multi-Center Study to Investigate the Efficacy and Safety of Once Daily Mexiletine PR During 26 Weeks of Treatment in Patients With Myotonic Dystrophy Type 1 and Type 2 (Phase 3)

A Randomized, Double-blind, Placebo-Controlled, Multi-Center Study to Investigate the Efficacy and Safety of Once Daily Mexiletine PR During 26 Weeks of Treatment in Patients with Myotonic Dystrophy Type 1 and Type 2 (HERCULES study)

Study website: https://myotonicdystrophystudy.com/

Read the detailed description

This is a multicenter, randomized, double-blind, parallel-group, placebo-controlled study intended to evaluate the efficacy and the safety of mexiletine PR in patients with myotonic dystrophy type 1 and type 2 (DM1 and DM2). The study will consist of a 4- week screening period and a 26-week treatment phase with patient visits at screening, baseline, Weeks 1, 2, 14, and 26. Eligible patients will be randomized to mexiletine or placebo in a 1:1 ratio. Approximately 80 DM1 patients (40 active: 40 placebo) are planned to be enrolled. For the purpose of sample size re-estimation, an interim analysis will be conducted when a total of 40 patients in total complete/early terminate the study.

In addition, 16 DM2 patients are planned to be enrolled (sub-group - 8 active: 8 placebo).

Study website: https://myotonicdystrophystudy.com/

Being tested
Mexiletine granules for prolonged-release oral suspension, Placebo
Medical subject headings
Myotonic Dystrophy

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • Mexiletine granules for prolonged-release oral suspensionDrug

    Mexiletine PR

  • PlaceboDrug

    Matching Placebo

Study groups in NCT06523400
Study groupRoleWhat they receive
PlaceboPlacebo comparator0 mg (matching sachet volumes to low, medium and high dose active drug)
Receives: Drug: Placebo
Mexiletine prolonged-release (PR)Active comparatorMexiletine PR 167 mg (mexiletine HCl 200 mg) Mexiletine PR 333 mg (mexiletine HCl 400 mg) OR Mexiletine PR 500 mg (mexiletine HCl 600 mg)
Receives: Drug: Mexiletine granules for prolonged-release oral suspension

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. To assess the efficacy of once daily mexiletine PR for the symptomatic treatment of myotonia in patients with myotonic dystrophy type 1 and type 2 (DM1 and DM2).

    Handgrip relaxation time in DM1 patients by mean change in baseline of handgrip relaxation time (seconds) after maximal voluntary isometric contraction (MVIC)

    Measured: 26 weeks

Secondary outcomes (19)
  1. To assess the safety of once daily mexiletine PR for the symptomatic treatment of myotonia in patients with myotonic dystrophy type 1 and type 2 (DM1 and DM2).

    Number and frequency of AEs/SAEs throughout the study while on treatment

    Measured: 26 weeks

  2. Mean change in VAS

    Score for muscle stiffness (myotonia severity) as self-reported by patients on a Visual Analog Scale (VAS)

    Measured: 26 weeks

  3. Mean change in MBS scores

    Mean change in Myotonia Behavior Scale (MBS) scores

    Measured: 26 weeks

  4. Mean change in health-related quality of life

    Mean change in health-related quality of life (measured by INQoL)

    Measured: 26 weeks

  5. Mean change in DM1-Activ-c scale (DM1 patients only)

    Mean change in measure of activity and social participation (measured by a Rasch-built scale with a 0-100 interval range)

    Measured: 26 weeks

  6. Mean change in time to perform the 10-meter Walk Test

    Mean change in time (seconds) to perform the 10-meter Walk Test (10mWT)

    Measured: 26 weeks

  7. Mean change in handgrip relaxation time

    Mean change in maximal voluntary isometric contraction (MVIC) and relaxation time by Video-recording of Hand Opening Time (VHOT) functional evaluation

    Measured: 26 weeks

  8. Mean change in time to perform Timed-up and go (TUG) test

    Mean change in time (seconds) to perform Timed-up and go (TUG) test

    Measured: 26 Weeks

  9. Mean change in health-related quality of life measured by EQ-5D

    Mean change in health-related quality of life measured by EQ-5D (5-point scale)

    Measured: 26 weeks

  10. Mean change in Myotonic Dystrophy Health Index (MDHI) score (DM1 patients)

    Mean change in Myotonic Dystrophy Health Index (MDHI) score (DM1 patients) as measured by patient's perceived health

    Measured: 26 weeks

  11. Mean change in Myotonic Dystrophy 2 Health Index (MD2HI) score (DM2 patients)

    Mean change in Myotonic Dystrophy 2 Health Index (MDHI) score (DM2 patients) as measured by patient's perceived health

    Measured: 26 weeks

  12. Assess the safety of mexiletine PR by changes in ECG

    Mean change in ECG (PR, QRS, QTc intervals, average HR) from baseline

    Measured: 26 weeks

  13. Assess the safety of mexiletine PR by AEs

    Incidence of treatment emergent adverse events (TEAEs), treatment-related TEAEs, serious AEs, and patient discontinuation rate

    Measured: 26 weeks

  14. Assess the safety of mexiletine PR by standard clinical laboratory evaluations

    Assess the safety of mexiletine PR by standard clinical laboratory evaluations as measured by hematology, chemistry, and urinalysis assessments from change in baseline

    Measured: 26 weeks

  15. Assess the safety of mexiletine PR by vital signs

    Assess the safety of mexiletine PR by vital signs (pulse, respiration, body temperature, and blood pressure) from change in baseline

    Measured: 26 weeks

  16. Assess the safety of mexiletine PR by physical examinations

    Assess the safety of mexiletine PR by change in baseline from physical examinations

    Measured: 26 weeks

  17. To assess the pharmacokinetics of mexiletine PR

    To assess the pharmacokinetics of mexiletine PR as measured by PK parameter AUC0-t

    Measured: 26 weeks

  18. To assess the pharmacokinetics of mexiletine PR by AUC0-t

    To assess the pharmacokinetics of mexiletine PR as measured by PK parameter AUC0-t (area under the concentration-time curve from time zero to last timepoint)

    Measured: 26 weeks

  19. To assess the pharmacokinetics of mexiletine PR by Cmax

    To assess the pharmacokinetics of mexiletine PR as measured by PK parameter Cmax (maximum plasma concentration)

    Measured: 26 weeks

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted26 Jul 2024
  2. Study start13 Feb 2025
  3. Primary completionJun 2027 (estimated)
  4. Study completionJun 2027 (estimated)

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 3
Primary purpose
Treatment
Allocation
Randomised
Intervention model
Single group
Model description
A multicenter, randomized, double-blind, parallel-group, placebo-controlled study intended to evaluate the efficacy and the safety of mexiletine PR in patients with myotonic dystrophy type 1 and type 2 (DM1 and DM2). The study will consist of a 4-week screening period and a 26-week treatment phase with patient visits at screening, baseline, Weeks 1, 2, 14, and 26. Eligible patients will be randomized to mexiletine or placebo in a 1:1 ratio. Approximately 80 DM1 patients (40 active: 40 placebo) are planned to be enrolled. For the purpose of sample size re-estimation, an interim analysis will be conducted when a total of 40 patients complete/early terminate the study. In addition, 16 DM2 patients are planned to be enrolled (sub-group - 8 active: 8 placebo).
Masking
Quadruple blind
Who is masked
Participant, Care provider, Investigator, Outcomes assessor
Enrolment
176 participants (estimated)
IDs, dates and publications
ClinicalTrials.gov ID
NCT06523400
Sponsor's protocol ID
MEX-DM-302
Status last verified
Sep 2026
First submitted
3 May 2024
Last updated
24 Sep 2026
Results posted
No
Data monitoring committee
Yes
FDA-regulated drug
No
FDA-regulated device
No
Individual data sharing
No

Questions about this trial

What is this clinical trial studying?

A Phase 3 study testing Mexiletine granules for prolonged-release oral suspension in people with Myotonic Dystrophy, run by Lupin Ltd. at 7 sites in 6 countries.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 11 inclusion and 28 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: looking for participants now, as of the sponsor's last update on 24 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 7 sites in United Kingdom, Belgium, Denmark, Germany, Italy and 1 more country. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

This study is still under way. Results are not available in the source record yet.

How can a doctor refer a patient or contact the research team?

Contact Nikki Adetoro (1 443-447-4534, nikkiadetoro@lupin.com), or a site near the patient. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

To assess the efficacy of once daily mexiletine PR for the symptomatic treatment of myotonia in patients with myotonic dystrophy type 1 and type 2 (DM1 and DM2). (time frame: 26 weeks). It is what the study was designed to measure, not a finding.

Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 24 Sep 2026.

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