To Assess Effects of Arbaclofen ER Tablets Compared With Placebo on Sperm Parameters in Male Subjects With MS

Primary Objective: The primary safety objective is to assess the effects of arbaclofen ER tablets (AERT) compared with placebo on sperm concentration from baseline to the end of 90 days of treatment in male subjects with MS. Secondary Objectives: The secondary safety objectives are to assess: * The effects of AERT compared with placebo on the following sperm parameters from baseline to the end of 90 days of treatment in male subjects with MS: * Semen volume and total sperm count per ejaculate; * Sperm motility; * Sperm morphology; and * Plasma levels of reproductive hormones: Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and total testosterone; * The recovery of subjects with 50 % decrease in sperm parameters 90 days after the discontinuation of IP; and * The safety and tolerability of IP.