Mexiletine in Sporadic Amyotrophic Lateral Sclerosis (Mexiletine-2)

Inclusion Criteria:

1. Sporadic ALS diagnosed as possible, laboratory-supported probable, probable, or definite ALS as defined by revised El Escorial criteria.
2. Age 18 years or older.
3. Symptom onset of weakness or spasticity due to ALS ≤ 60 months prior to Screening Visit.
4. Slow vital capacity (SVC) measure ≥50% of predicted for gender, height, and age at the screening visit.
5. Must be able to swallow capsules throughout the course of the study, according to Site Investigator judgment.
6. Capable of providing informed consent and following trial procedures.
7. For TMS: a resting motor threshold defined as 50% of pulses eliciting a motor evoked potential (MEP) of amplitude ≥ 50 µV.
8. For TTNCS: median Compound Muscle Action Potential (CMAP) ≥ 1.5 mV.
9. Subjects must not have taken riluzole for at least 30 days or be on a stable dose of riluzole for at least 30 days prior to the Screening Visit and continue on the stable dose throughout the course of the study (riluzole-naïve subjects are permitted in the study).
10. Subjects must not have taken edaravone for at least 30 days or be on a stable dose of edaravone for at least 30 days prior to the Screening Visit and continue on the stable dose throughout the course of the study (edaravone-naïve subjects are permitted in the study).
11. Subjects must not have taken medication for muscle cramping such as cyclobenzaprine, baclofen, carisoprodol, or methocarbamol, for at least 30 days prior to screening or be on a stable dose for at least 60 days prior to screening.
12. Geographic accessibility to the site.
13. Women must not become pregnant for the duration of the study and must be willing to use two contraceptive therapies and have a negative pregnancy test throughout the course of the study.
14. Use of medications known to affect the neurophysiology measures in the study must be scheduled, not as needed (pro re nata, PRN). A subject must have been on a fixed dose for 30 days prior to the Screening Visit, and there must be no reason to believe that a subsequent change would be necessary during the course of the study. These medications include: benzodiazepines, muscle relaxants, tricyclic antidepressants, selective serotonin reuptake inhibitors, non-selective serotonin reuptake inhibitors, hypnotics (including anti-histamines) and anti-cholinergics.

Exclusion Criteria:

1. Invasive ventilator dependence, such as tracheostomy.
2. Creatinine level greater than 1.5 mg/dL at screening.
3. Serum Glutamic-Oxaloacetic (SGOT/AST) / Serum Glutamic-Pyruvic (SGPT/ALT) greater than 3 times the upper limit of normal at screening.
4. History of known sensitivity or intolerability to mexiletine or lidocaine.
5. Any history of either substance abuse within the past year, unstable psychiatric disease, cognitive impairment, or dementia.
6. Clinically significant conduction abnormalities on electrocardiogram or a known history of cardiac arrhythmia.
7. Known history of epilepsy.
8. Known history of congestive heart failure (CHF) or history of myocardial infarction within the past 24 months.
9. Use of mexiletine for 60 days prior to Screening Visit.
10. Exposure to any other experimental agent (off-label use or investigational) including high dose creatine (>10 grams a day) within 30 days prior to Screening Visit.
11. Metal in the head and neck region, cardiac pacemaker or brain stimulator, cochlear implants, implanted infusion device or personal history of epilepsy.
12. Use of amiodarone, flecainide, duloxetine, tizanidine, or clozapine.
13. Pregnant women or women currently breastfeeding.
14. Placement of Diaphragm Pacing System (DPS) device < 60 days prior to Screening Visit.
15. Planned DPS device implantation during study participation