This is a randomized, double-blind, active comparator-controlled study with a parallel-group design including four arms with X842 and one arm with Lansoprazole.~Randomization to one of the treatments with X842 twice daily (BID) 25 mg, 50 mg, 75 mg, 100 mg, or Lansoprazole 30 mg once daily (QD) will be based on a 1:1:1:1:1 scheme.~The duration of each patient's participation in the study, including screening, blind treatment period, and open-label treatment period will be approximately 60 days. The patients will be randomized for 4 weeks of double-blind treatment and will be provided with investigational medicinal product for 35 days.~All patients will have an endoscopic evaluation after 4 weeks of treatment. Following the endoscopic evaluation, all patients will receive subsequent 4 weeks of open-label treatment with Lansoprazole. Repeated symptom evaluation to detect symptom patterns will be assessed during this period.
This study will be conducted in patients with erosive esophagitis due to gastro-esophageal reflux disease (GERD) Los Angeles (LA) grades C or D, and in patients with at least partial symptom response but still endoscopically unhealed (LA grades A or B) after 8 weeks history of standard treatment healing course with PPI, designed to support dose selection for Phase 3 and to investigate safety, tolerability, and healing rates after 4 weeks treatment of X842 or Lansoprazole, and symptom pattern during subsequent 4 weeks treatment with Lansoprazole.