We aimed to compare the efficacy of genotypic resistance guided sequential therapy vs. empiric therapy in the third line therapy. Factors affecting the eradication rates, including the antibiotic resistance, CYP2C19 polymorphism, CagA and VacA status will also be assessed.

The primary aim of this study is to compare the regimens selected using either one of the method (1) genotypic resistance guided versus (2) medication history guided therapy. (rather than to compare the efficacy of any drugs).

Inclusion Criteria:

• Patients aged greater than 20 years who have persistent H. pylori infection after at least two treatments and are willing to receive third line rescue regimens are considered eligible for enrollment.

Exclusion Criteria:

• Patients will be excluded from the study if any one of the following criteria is present: (1) children and teenagers aged less than 20 years, (2) history of gastrectomy, (3)gastric malignancy, including adenocarcinoma and lymphoma, (4) previous allergic reaction to antibiotics (Amoxicillin, Klaricid, Cravit) and prompt pump inhibitors (esomeprazole), (5)contraindication to treatment drugs, (6) pregnant or lactating women, (7) severe concurrent disease.