Intervention: patients with Helicobacter pylori eradication treatment failure are recruited and randomly assigned to receive one of the following therapeutic schemes: 1) study group: rabeprazole 20mg bid + amoxicillin 1g bid + clarithromycin 0.5g bid + N-acetylcystein 0.6g bid for 10 days; 2) control group: rabeprazole 20mg bid + amoxicillin 1g bid + clarithromycin 0.5g bid + metronidazole 0.5g bid for 10 days. Repeat upper endoscopy for histologic evaluation, rapid urease test or 13C-urea breath test after 4 week of treatment to assess the treatment result. The influence on the hybrid therapies of antibiotic resistance of Helicobacter pylori and CYP2C19 genotype of host were determined.