Study of Nighttime Dosing of Sublingual Tizanidine (12 mg) in Multiple Sclerosis (MS) Patients With Significant Spasticity

Inclusion Criteria: * Male and female patients between the ages of 20-65 * Definitive diagnosis of MS, with Expanded Disability Status Scale (EDSS) less than 6.5 at screening * Has significant spasticity (total Ashworth =\> 6) at screening * Can maintain sleep regimens of at least 5 hours nightly for study duration * May be allowed to take other anti-spasticity medication during study (including oral baclofen) as per individual dosing regimen, with the following qualifications: * No dose after 6pm on any study day * No dose at all on a clinic evaluation day (Visits 3, 4, 5) * Females must agree to use a medically accepted form of birth control, be surgically sterile, or be two years post-menopausal. Oral contraception is contraindicated with tizanidine use. Exclusion Criteria: * Acute MS exacerbation requiring treatment with steroids within 30 days of screening * Initiation of discontinuation of interferon beta within 30 days of screening * Use of baclofen pump * Use of CYP1A2 inhibitors during study * Taking medications that would potentially interfere with the actions of the study medication or outcome variables, including: sedatives, stimulants, anti-hypertensives, tricyclic antidepressants, etc. * Previous diagnosis of a sleep disorder, distinct from MS, such as obstructive sleep apnea or narcolepsy * Score \>18 on Beck Depression Inventory at screening * Changes in chronic oral medications within 2 weeks of baseline and during study * Significant abnormalities in screening lab parameters (ex: ALT, AST, bilirubin \> 2 x upper limit of normal \[ULN\]; creatinine \> 2 mg/dl; white blood cell \[WBC\] \< 2,300; platelets \< 80,000). * Previous history of dementia, unstable psychiatric disease, or current signs and symptoms of significant medical disorders such as severe, progressive, or uncontrolled renal, hepatic, hematological, endocrine, pulmonary, cardiac, neurological, or cerebral disease * History of allergy to tizanidine or any inactive component (including lactose intolerance) of test or reference formulation * History of substance abuse within the past 12 months * Within 30 days of baseline, worked a rotating or nighttime shift * Participation in another clinical trial within 30 days of baseline * Patients who are uncooperative or unwilling to sign consent form