Inclusion Criteria:

• Male or female at least 18 years old.
• Agrees to use a medically acceptable method of contraception throughout the study
• Diagnosed with MS as defined by Poser or McDonald Criteria.
• Receiving commercial baclofen tablets at a stable total daily dose ranging from 15 mg to 80 mg in a TID dosing regimen for at least 4 weeks prior to the Screening Visit that has resulted in improved spasticity.
• Willing to wash out and remain off other antispasticity medications during the study.

Exclusion Criteria:

• If female, the subject is pregnant, planning to become pregnant, or breastfeeding.
• History of allergy or severe intolerance to baclofen.
• Did not respond to previous baclofen treatment in any formulation.
• Has experienced an exacerbation of MS within 1 month.
• Urinary tract infection (UTI) within 2 weeks or two symptomatic UTIs within 6 months prior to the study.
• Subjects with clinically significant impairment of renal function
• History of active seizure disorder or epilepsy, or currently taking an anticonvulsant for treatment or control of seizure.
• Other conditions causing spasticity (e.g., stroke, cerebral palsy, traumatic brain injury) or rigidity (e.g. Parkinson's Disease).
• Treated with Botulinum Toxin Type A or B within the previous 4 months, or with phenol or therapeutic alcohol nerve block within 12 months or planned use of these drugs during this study.
• Has clinically significant limitation of passive range of motion of lower extremities.
• Has had major surgery within 6 months prior to Screening Visit that may affect spasticity assessments such as abdominal surgery, back surgery, lower leg and knee surgeries.