Study of Safety, Tolerability & Efficacy of CK-2017357 in Amyotrophic Lateral Sclerosis (ALS)

Inclusion Criteria: 1. Able to comprehend and willing to sign an Informed Consent Form (ICF) 2. Male or female 18 years of age or older 3. A diagnosis of familial or sporadic ALS (defined as meeting the possible, laboratory-supported probable, probable, or definite criteria for a diagnosis of ALS according to the World Federation of Neurology El Escorial criteria) 4. Upright Slow Vital Capacity (SVC) \>50 % of predicted for age, height and sex 5. At least 4 of the 12 ALSFRS-R questions must be scored 2 or 3 6. Diminished but measurable maximum voluntary grip strength in at least one hand; i.e., between 10 and 50 pounds (females) and 10 and 70 pounds (males) 7. Able to swallow tablets without crushing 8. A caregiver (if one is needed) who can and will observe and report the patient's status 9. Pre-study clinical laboratory findings within normal range or, if outside of the normal range, deemed not clinically significant by the Investigator 10. Male patients must agree for the duration of the study and 10 weeks after the end of the study to use a condom during sexual intercourse with female partners who are of reproductive potential and to have female partners use an additional effective means of contraception (e.g., diaphragm plus spermicide, or oral contraceptives) or the male patient must agree to abstain from sexual intercourse during and for 10 weeks after the end of the study 11. Female patients must be post-menopausal (≥ 1 year) or sterilized, or, if of childbearing potential, not be breastfeeding, have a negative pregnancy test, have no intention to become pregnant during the course of the study, and use contraceptive drugs or devices as detailed in item 10 for the duration of the study and for 10 weeks after the end of the study 12. Patients must be either on a stable dose of riluzole 50 mg twice daily for at least 30 days prior to screening or have not taken riluzole for at least 30 days prior to screening and are willing not to begin riluzole use during the conduct of this study. Exclusion Criteria: 1. Any use of non-invasive positive pressure ventilation (NIPPV, e.g. continuous positive airway pressure \[CPAP\] or bilevel positive airway pressure \[BiPAP\]) for any portion of the day, or mechanical ventilation via tracheostomy, or on any form of oxygen supplementation 2. Patients with a diaphragm pacing system (DPS) at study entry or who anticipate DPS placement during the course of the study 3. Body Mass Index (BMI) of 19.0 kg/m2 or lower 4. Unwilling to discontinue tizanidine and theophylline-containing medications during study participation 5. Serum chloride \< 100 mmol/L 6. Neurological impairment due to a condition other than ALS, including history of transient ischemic attack (TIA) within the past year 7. Presence at screening of any medically significant cardiac, pulmonary, gastrointestinal (GI), musculoskeletal, or psychiatric illness that might interfere with the patient's ability to comply with study procedures or that might confound the interpretation of clinical safety or efficacy data 8. Has taken any investigational study drug within 30 days or 5 half-lives of the prior agent, whichever is greater, prior to dosing 9. Previously received CK-2017357 in any previous clinical trial