Proton pump inhibitors (PPIs) are mainly metabolized in the liver by CYP2C19, one of the cytochrome P450 isoenzymes, which shows a genetic polymorphism associated with enzyme activities. The most essential role of a PPI in H. pylori eradication therapy is to make antibiotics more stable and bioavailable in the stomach by raising intragastric pH to neutral levels.

Most patients who have failed in the eradication of H. pylori infection by triple therapy with a PPI, amoxicillin (AMPC) and clarithromycin (CAM) at standard doses have extensive metabolizer (EM) genotypes of CYP2C19 and/or are infected with CAM-resistant strains of H. pylori.

Four-times daily dosing of a PPI could achieve complete gastric acid inhibition. Dual therapy with 4-times daily dosing of a PPI and AMPC could yield sufficient re-eradication rates in patients with EM genotype of CYP2C19.

Metronidazole (MNZ)-based re-eradication therapy, such as triple PPI/AMPC/MNZ therapy, also achieved high eradication rates and has been recommended as the second line therapy in Japan. But carcinogenic actions of MNZ have been unclear.

The purpose of this study is to compare the re-eradication rates of H. pylori infection by the dual high-dose PPI/AMPC therapy and triple PPI/AMPC/MNZ therapy, and to validate the efficacies of these re-eradication regimens as second line eradication therapies.

Inclusion Criteria:

• Patients with H. pylori infection

Exclusion Criteria:

• Patients without H. pylori infection