To evaluate the efficacy and safety of X842 Capsules 50 mg compared to Lansoprazole Enteric Capsules for the treatment of reflux esophagitis, and to characterize the population pharmacokinetics of X842 capsules in this patient population.

This study uses a multicenter, randomized, double-blind, double-dummy, active-controlled parallel-group, non-inferiority design to compare the efficacy and safety of X842 capsules (50 mg) in the treatment of reflux esophagitis over 4 to 8 weeks in comparison with lansoprazole enteric-coated capsules(30 mg) . Additionally, the population pharmacokinetics characteristics of X842 capsules in patients with reflux esophagitis is observed.

Inclusion Criteria:

1. Males or females, 18 years ≤ age ≤ 75 years;
2. Within 7 days prior to randomization, the subjects are endoscopically diagnosed with reflux esophagitis from Los Angeles (LA) grade A to D (notes: the percent of the subjects with LA grade A of RE should be no more than 20% of the all subjects who are planned to be enrolled in the study);
3. Subjects who can independently complete the subject diary cards;
4. Subjects fully understand the trial contents, participate in the trial voluntarily, and sign the informed consent forms.

Exclusion Criteria:

1. Subjects who receive X842 capsules or other P-CAB drugs in previous clinical studies;
2. Subjects known to be allergic to X842 capsules or lansoprazole enteric-coated capsules, or relevant excipients of X842 capsules or lansoprazole enteric-coated capsules, such as lactose, microcrystalline cellulose, croscarmellose sodium, sodium dodecyl sulfate, sodium stearyl fumarate, and silicon dioxide;
3. Subjects unable to receive upper gastrointestinal endoscopy;
4. Endoscopic examination revealed concomitant diseases potentially affecting the esophagus, excluding hiatal hernia, and excluding Barrett's esophagus with metaplastic columnar epithelium that either does not involve the entire esophageal circumference or is short-segment (< 3 cm in length).
5. Patients with rheumatic/autoimmune diseases potentially affecting esophageal motility (e.g., scleroderma, undifferentiated connective tissue disease), or those with a history of esophageal radiotherapy or cryotherapy;
6. Subjects who have acute upper gastrointestinal hemorrhage within 4 weeks prior to enrollment;
7. Subjects with active peptic ulcer discovered during upper gastrointestinal endoscopy, or subjects with suspicious or definite malignancies;
8. Subjects known to have Zollinger-Ellison syndrome or inflammatory bowel disease (IBD);
9. Subjects with history of surgery affecting the structure or function of the esophagus, stomach, or duodenum, or surgery altering gastric acid secretion.
10. Subjects who plan to undergo surgical procedures during the study period that may alter gastric acid secretion (e.g., abdominal surgery, vagotomy, or craniectomy).
11. Subjects with a history of malignancies within 5 years prior to screening (a subject can participate in the study if his /her skin basal cell carcinoma or carcinoma in situ of uterine cervix has been cured);
12. Subjects with concomitant serious diseases of central nervous system, cardiovascular system, respiratory system, liver, kidney, gastrointestinal tract, urinary system, endocrine system, or hematological system, and the investigator thinks these diseases may mix the study results up or affect the safety of the subject;
13. Laboratory test results at screening showing that ALT or AST is larger than 1.5 times of the upper limit of normal, or kidney function index Cr is larger than the upper limit of normal (a re-examination is permitted in the study, and subjects will be excluded if they still fail to meet the inclusion criteria);
14. Subjects who use of therapeutic doses of GERD medications within 7 days prior to randomization, eg. proton pump inhibitors (PPIs), P-CABs, histamine2 receptor antagonists (H2RAs), or gastric mucosal protectors (except hydrotalcite), prokinetic drugs, and traditional Chinese medicines;
15. Subjects who chronically use non-steroidal anti-inflammatory drug (including cyclooxygenase-2 inhibitor), anti-platelet drug (such as aspirin and clopidogrel), or anticoagulant (such as Warfarin) prior to randomization, and can not stop the medication during the trial;
16. At screening, subjects with clinically significant ECG abnormalities, including serious arrhythmia, multifocal ventricular premature complexes, grade II or above atrioventricular block, and prolongation of the Q-Tc interval (QTc≥450 ms in males and QTc≥470 ms in females);
17. Subjects who are using atazanavir sulfate or ripivirin hydrochloride at screening;
18. Subjects with a history of long-term abuse of drug or alcohol within 6 months prior to screening;
19. Female subjects with known pregnancy, those in breast-feeding period, or those who are planned to become pregnant during the trial. At the investigator's discretion, women of childbearing age who cannot use a medically-proven and reliable method of contraception from signing the informed consent forms to 4 weeks after the last dose of the study;
20. Subjects who participate in other drug/medical device clinical studies and use the drug/medical device within 3 months prior to randomization;
21. Subjects who are considered unsuitable for participating in this trial by investigators.

This trial uses a double-blind double-dummy design, where the investigator, the subject and the other parties involved in the trial are blinded to the drug given to the subject. X842 capsules (test group)and and placebo, lansoprazole enteric-coated capsules (control group)and placebo, are provided by Jiangsu Sinorda Biomedicine Co., Ltd. The physical appearance, shape, specification and dosage of the test drug and comparator as well as the placebo are generally similar.