 Rescue regimen for treatment failure after first-line regimen Patients who remained positive for H. pylori after the initial treatment as determined by the 13C-UBT will be followed by endoscopy. Biopsy will be done for H. pylori culture and antibiotic susceptibility test. All of them will then be treated with rescue regimen. The rescue regimens will be given in a cross-over manner Figure 1. Patients who are treated with CALa regimen for 7 days as initial treatment will be treated with LALa regimen for 10 days as rescue treatment. Patients who are treated with LALa regimen for 7 days as initial treatment will be treated with CALa regimen for 10 days as rescue treatment. 