IPX056 in Subjects With Established Spasticity Resulting From Multiple Sclerosis

The primary objective of this study is to demonstrate that IPX056 reduces spasticity, measured by Ashworth score, in subjects with multiple sclerosis (MS). This study will also (1) assess the correlation between pharmacokinetic (PK) and pharmacodynamic (PD) endpoints (Ashworth score), and (2) quantify the duration of pharmacodynamic effects for IPX056 as well as marketed baclofen tablet in subjects with Multiple Sclerosis (MS) after a single dose. Additionally, the efficacy parameters, including Multiple Sclerosis Impact Scale (MSIS)-29, spasm frequency and nighttime awakening score, spasticity control, morning stiffness, and Global Assessment of Efficacy and Tolerability, will be assessed during open-label extension period. The safety of IPX056 will be monitored throughout the study. This study consists of 2 parts: Part I (Screening Visit \& Visit 1) of the study is a single-dose, double-blind, randomized, placebo- and active comparator-controlled, parallel group design containing a single 12 hour PK/PD evaluation period. Part II is an optional, approximately 9-week open-label extension study and will start during Visit 1, immediately after Visit 1 PK/PD procedures are completed.