Study to Evaluate the Safety & Efficacy of FLX-787-ODT to Treat Fasciculations in Tongue and Upper or Lower Extremity Muscles Most Affected in Subjects With ALS

Inclusion Criteria: * Documented diagnosis of ALS diagnosis of less than 3 years. * Expected survival \> 6 months * Frequent fasciculations noted during clinical examination of any single muscle (\>6 visible fasciculations per minute) observed in Part I * Normal oral cavity exam at screening * Proficient in English * Male subjects will either be surgically sterile or agree to use a medically acceptable method of contraception during sexual contact with females of childbearing potential, and will refrain from sperm donation for 45 days following the study * Male subjects will either be surgically sterile or agree to use a medically acceptable method of contraception during sexual contact with females of childbearing potential, and will refrain from sperm donation for 45 days following the study Exclusion Criteria: * Presence of clinically significant or unstable condition that would result in an increased risk of study participation or difficulty in interpretation of the study results * Tremor or other movement disorder that would interfere with recording * Inability to lie flat * Presence of major gastrointestinal disorders, such as inflammatory bowel disease, diverticulitis, active peptic ulcer disease, or significant gastroesophageal reflux disease (i.e., not well-controlled on antacids or proton pump inhibitors), or oral or esophageal lesions/ulcers * Presence of laryngospasm or significant swallowing problems * Presence of percutaneous endoscopic gastrostomy, esophagogastroduodenoscopy, or G-tube * Inability to tolerate a spicy sensation in the mouth or stomach * Actively using illicit drugs or history of chronic substance abuse within the past year prior to screening, including abuse of alcohol * Participated in a clinical study (except natural history studies without administration of an investigational product) within 30 days prior to screening * Pregnant, breastfeeding, or planning to become pregnant * Blood pressure of ≥160 mmHg systolic and/or ≥100 mmHg diastolic * Clinically significant abnormalities in laboratory findings (including screening complete electrolyte panel, complete blood count, liver function tests).