A Study in Patients With Erosive Esophagitis 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

Inclusion Criteria

• Body mass index (BMI) ≥ 18 and ≤ 40 kg/m^2 at screening.
• Gastro-esophageal reflux disease with endoscopically confirmed esophagitis:
• LA grade C or D ≤7 days before randomization (with or without historical PPI treatment) or
• LA grade A or B ≤7 days before randomization and history of treatment with the standard healing course of PPI for minimum of 8 weeks prior to screening and ≤7 days of non-treatment during this period and at least partial symptom response during the minimum of 8 weeks of PPI treatment.
• Willing and able to comply with all aspects of the protocol (including capsule swallowing, diary completion, etc.).
• Capable of signing informed consent form.

Exclusion Criteria

• History or presence of any clinically significant cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrine, hematological, or neurological disease or disorder.
• Patients with so-called "alarm features" in symptomatology, like odynophagia, severe dysphagia, bleeding, weight loss, anemia, and blood in stool pointing to a possible malignant disease of the gastrointestinal (GI) tract.
• Present clinically significant psychiatric diagnosis.
• History of malignancy of any organ system.
• Presence of esophageal ulcer, stricture, Barrett´s esophagus or suspected esophagitis secondary to infection, inflammatory disease, ingestion of erosive chemicals or history of any surgical or medical condition which might significantly alter the Gastro-oesophageal reflux disease (GERD) status or the absorption, distribution, metabolism or excretion of drugs.
• Known severe atrophic gastritis.
• Any planned major surgery within the duration of the study.
• History of a positive result for human immunodeficiency virus (HIV), Hepatitis B surface antigen (HBsAg), antibody to Hepatitis B core antigen (anti-HBcAg), or antibody to Hepatitis C virus (anti-HCV) or presence of these findings on screening.
• History of long QTc syndrome (e.g. QTc ≥450 ms for males and ≥470 ms for females).
• Cardiac arrhythmias or any clinically significant abnormalities in the resting 12-lead ECG at the time of screening, as judged by the Investigator.
• History of severe allergy/hypersensitivity or ongoing allergy/hypersensitivity.
• Current or history of alcohol, drug abuse and/or use of anabolic steroids within 2 years prior to screening.
• Women who are pregnant or breastfeeding.
• Patients who have previously participated (completed or withdrawn) in this study CX842A2201.