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

Exclusion Criteria28

• 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;
• 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