This is a multicenter, randomized, double-blind, placebo-controlled, parallel-group study to evaluate the safety and efficacy of oral arbaclofen ER tablets in MS patients with spasticity. Arbaclofen ER will be compared with placebo.

This is a multicenter, randomized, double-blind, placebo-controlled, parallel-group study to evaluate the safety and efficacy of oral arbaclofen ER tablets (80 mg/day) in MS patients with spasticity. Arbaclofen ER will be compared with placebo. The treatment groups will be randomized in a 1:1 ratio. There will be a 49-day dose escalation period, followed by a 84-day maintenance treatment period, followed by a 21-day taper period.

Inclusion Criteria:

• Subjects 18 to 65 years of age, inclusive
• An established diagnosis per McDonald Criteria (Polman et al 2011) of MS (either RR or SP course) that manifests a documented history of spasticity for at least 6 months prior to screening
• Spasticity due to MS as shown by a TNmAS-MAL score ≥ 2
• Expanded Disability Status Scale (EDSS) score greater than or equal to (≥) 3.0 and less than or equal to (≤) 7.0
• 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:

• Any concomitant disease or disorder that has symptoms of spasticity or that may influence the subject's level of spasticity
• In the opinion of the investigator, the patient is unable to rate their level of spasticity or distinguish it from other MS symptoms
• 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
• Current significant cognitive deficit, severe or untreated anxiety, severe or untreated depression
• 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