A Study to Investigate the Safety and Effectiveness of Arbaclofen Extended-Release Tablets for Patients With MS

Inclusion Criteria Includes: * Subjects 18 to 65 years of age, inclusive. * An established diagnosis of MS that manifests a documented history of spasticity. * If receiving disease-modifying medications (eg, interferons approved for MS, glatiramer acetate, natalizumab, fingolimod, or mitoxantrone), there must be no change in dose for at least 3 months prior to Visit 1 (Screening), and the subject must be willing to maintain this treatment dose for the duration of the study. If receiving AMPYRA® (dalfampridine, fampridine, 4-amino puridine), subject must be at a stable dose for at least 3 months prior to Visit 1. * Stable regimen for at least 3 months prior to Visit 2 for all medications and non-pharmacological therapies that are intended to alleviate spasticity. * Absence of infections, peripheral vascular disease, painful contractures, advanced arthritis, or other conditions that hinder evaluation of joint movement. * Use of a medically highly effective form of birth control (see Section 7.8) during the study and for 3 months thereafter for women of child-bearing potential (including female subjects and female partners of non-sterile male subjects). * Willing to sign the informed consent form (ICF). Exclusion Criteria Includes: * Any concomitant disease or disorder that has symptoms of spasticity or that may influence the subject's level of spasticity. * Concomitant use of medications that would potentially interfere with the actions of the study medication or outcome variables. * Pregnancy, lactation, or planned pregnancy during the course of the study and for 3 months after the final study visit. * Subject has clinically significant abnormal laboratory values, in the opinion of the investigator, at Visit 1 or Visit 2. * Current malignancy or history of malignancy that has not been in remission for more than 5 years, except effectively treated basal cell skin carcinoma. * Any other significant disease, disorder, or significant laboratory finding which, in the opinion of the investigator, puts the subject at risk because of participation, influences the result of the study, or affects the subject's ability to participate.