Open-label Extension Study in Paediatric Patients Who Have Completed the MEX-NM-301 Study.

NCT04622553 | Active Not Recruiting

• 1 other identifier: MEX-NM-303
• Study Type: interventional
• Target: 14
• Locations: 1 country
• Sites: 1

Brief Summary

Open-label Extension Study to Evaluate the Long-term Safety and Efficacy of Mexiletine in Paediatric Patients with Myotonic Disorders Who Have Completed the MEX-NM-301 study.

Conditions

Myotonic Disorders

Outcome Measures

Primary Outcomes (5)

• Assess the long-term safety and tolerability of mexiletine by AEs

  Assess the long-term safety and tolerability of mexiletine in paediatric patients by number and frequency of AEs/SAEs, throughout the study while on treatment

  Approximately 24 months

• Assess the long-term safety and tolerability of mexiletine by hand relaxation

  Mean time (in seconds) to relaxation of hand muscles and reduction in relaxation time from the first to the fifth contraction

  Approximately 24 months

• Assess the long-term safety and tolerability of mexiletine measurement of AESI

  Assess the long-term safety and tolerability of mexiletine in paediatric patients by Incidence of adverse events of special interest (AESI),

  Approximately 24 months

• Assess the long-term safety and tolerability of mexiletine by changes in ECG

  Assess the long-term safety and tolerability of mexiletine in paediatric patients by changes in ECG assessments from baseline, repeated at each study visit

  Approximately 24 months

• Assess the long-term safety and tolerability of mexiletine by muscle stiffness

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

  Approximately 24 months

Secondary Outcomes (6)

• Mean change in VAS

  Approximately 24 months

• Clinical myotonia assessment

  Approximately 24 months

• Mean change in health-related quality-of-life

  Approximately 24 months

• Clinical Global Impression (CGI) scores

  Approximately 24 months

• Mean change in Myotonia Behaviour Scale (MBS) scores

  Approximately 24 months

Study Arms (1)

Cohort 1 and 2

OTHER

7 patients aged 12 to \< 18 years , inclusive in cohort-1 7 patients aged 6 to \< 12 years, inclusive in cohort-2

Drug: Mexiletine

Interventions

Mexiletine DRUG

Patients will be enrolled sequentially into 2 cohorts. Cohort 1 - (patients aged 12 to \< 18 years): approximately 8 weeks - 4 weeks of dose titration period + 4 weeks of maintenance period. Cohort 2- (patients aged 6 to \< 12 years,): approximately 8 weeks - 4 weeks of dose titration period + 4 weeks of maintenance period. Enrolment for Cohort 2 will begin after initial pharmacokinetics (PK), safety and efficacy are confirmed in this population, of patients in Cohort 1

Also known as: Namuscla ™

Cohort 1 and 2

Eligibility Criteria

• Age: 6 Years - 18 Years
• Sex: all
• Healthy Volunteers: No
• Age Groups: Child (0-17), Adult (18-64)

You may qualify if:

• Patients previously completed the parent study PIP study 4 (MEX-NM-301) and tolerated the Mexiletine in the study.
• Able and willing to provide assent to study participation and a parent or legal guardian willing to sign written informed consent prior to study entry.
• No significant cardiac abnormalities as determined by a cardiologist's assessment of the ECG and Echocardiogram
• No history or evidence of any significant liver disorder Laboratory investigations for haematology, biochemistry, and urinalysis at screening are within normal range, or showing no clinically relevant abnormal values, as judged by the Investigator
• Female patients of childbearing potential must be using an acceptable form of birth control as determined by the Investigator (e.g., oral contraception, implantable, injectable/transdermal hormonal contraception, intrauterine device (IUD), barrier methods), tubal ligation or have a vasectomized partner or are practicing abstinence

You may not qualify if:

• Any contra-indication to mexiletine (as described in the Namuscla Summary of Product Characteristics \[SmPC\])
• Hypersensitivity to the active substance, or to any of the excipients
• Hypersensitivity to any local anaesthetic
• Ventricular tachyarrhythmia
• Complete heart block (i.e., third-degree atrioventricular block) or any heart block susceptible to evolve to complete heart block (first-degree atrioventricular block with markedly prolonged PR interval (≥ 200 ms) and/or wide QRS complex (≥ 120 ms), second-degree atrioventricular block, bundle branch block, bifascicular and trifascicular block),
• QT interval \> 450ms
• Myocardial infarction (acute or past), or abnormal Q-waves
• Symptomatic coronary artery disease
• Heart failure with ejection fraction \<50%
• Atrial tachyarrhythmia, fibrillation or flutter
• Sinus node dysfunction (including sinus rate \< 50 bpm)
• Co-administration with medicinal products inducing torsades de pointes (class Ia, Ic, III antiarrhythmics): Co-administration of mexiletine and 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) increases the risk of potentially lethal torsades de pointes.
• Co-administration with medicinal products with narrow therapeutic index
• Co- administration with antiarrhythmics
• Any other neurological or psychiatric condition that might affect the assessment of the study measurements

Sponsors & Collaborators

• Lupin Ltd.: lead

Study Sites (1)

Hôpital Necker-Enfants-Malades

Paris, France

Location

MeSH Terms

Conditions

Myotonic Disorders

Interventions

Mexiletine

Condition Hierarchy (Ancestors)

Muscular Diseases; Musculoskeletal Diseases; Neuromuscular Diseases; Nervous System Diseases

Intervention Hierarchy (Ancestors)

Propylamines; Amines; Organic Chemicals; Phenyl Ethers; Phenols; Benzene Derivatives; Hydrocarbons, Aromatic; Hydrocarbons, Cyclic; Hydrocarbons

Study Officials

• Christine Barnérias, MD

  Hopital universitaire Necker-Enfants Malades

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NA
• Masking: NONE
• Purpose: TREATMENT
• Intervention Model: SINGLE GROUP
• Sponsor Type: INDUSTRY
• Responsible Party: SPONSOR

Model Details: The aim of this study is to obtain additional information regarding the long-term safety and efficacy of mexiletine for the symptomatic treatment of myotonia in paediatric subjects who have completed the initial paediatric study MEX-NM-301.

Study Record Dates

• First Submitted: October 22, 2020
• First Posted: November 10, 2020
• Study Start: November 5, 2021
• Primary Completion: January 26, 2026
• Study Completion: March 12, 2026
• Last Updated: July 25, 2025

Record last verified: 2025-07

Data Sharing

• IPD Sharing: Will not share

Locations

FR (1)