Inclusion Criteria:  Diagnosis of familial or sporadic ALS FVC of ≥ 50 percent predicted If female, is not breastfeeding and is not pregnant Has been on a stable dose of riluzole, or has not taken riluzole, for at least 30 days prior to screening If taking concomitant edaravone at study entry, must have completed at least one cycle of edaravone therapy prior to screening Not currently taking and has not taken for at least 30 days prior to screening any Theophylline containing medications, clozapine, or duloxetine No active infection in the 30 days prior to randomization Has not taken any fluoroquinolone antibiotics for at least 30 days prior to screening  Exclusion Criteria:  Hypersensitivity/allergy to fluoroquinolones Diagnosed with another neurodegenerative disease Significant pulmonary disorder not attributed to ALS, central nervous system disorder associated with seizures, myasthenia gravis, active rheumatologic disease, tendinopathy, or any severe uncontrolled medical condition (other than ALS) Severe renal impairment or impaired liver function Baseline prolongation of QT interval/corrected QT interval (QTc) at screening, treatment with any agent that may prolong Qt/QTc interval, or history of any other at-risk other cardiac condition Currently enrolled in another clinical trial involving an experimental drug or device