A Study to Evaluate the Efficacy and Safety of Arbaclofen Placarbil (XP19986) as Adjunctive Therapy in Subjects With Gastroesophageal Reflux Disease (GERD)

Inclusion Criteria: 1. confirmed diagnosis of GERD by a gastroenterologist 2. minimum of 3 months of GERD symptoms prior to screening. 3. currently taking an FDA approved dose of PPI therapy for symptomatic GERD for at least 4 weeks prior to screening 4. experienced partial relief of GERD symptoms while receiving approved dose and regimen of PPI therapy 5. experienced GERD symptoms, defined as heartburn (with or without regurgitation or other GERD symptoms) on ≥ 3 days during the week prior to screening Exclusion Criteria: 1. evidence of erosive esophagitis or erosive gastritis on upper gastrointestinal endoscopy during screening 2. has not experienced any GERD symptom improvement after an adequate course of PPI treatment (at least 2 weeks) 3. unstable or severe medical condition