10-day sequential therapy was not sufficient to overcome tough situation for H. pylori eradication in Korea due to high antimicrobial resistance. The present investigators assumed that doubling duration of second phase of sequential therapy might have more potent bactericidal efficacy than previous 10-day sequential regimen. But 15-day regimen with initial 5-day PPI with amoxicillin followed by remaining 10-day PPI, clarithromycin with metronidazole was not ever tested before. Moreover, whether extending the sequential therapy to 15-day might be more effective than 10-day sequential therapy is unknown especially in Korea. From this background, the present investigators prepared clinical trials regarding modified sequential therapy which was extending the treatment duration to 15 days compared than previous 10-day sequential therapy regimen. In addition, pre-treatment antimicrobial susceptibility testing was performed to find the possibility to overcome antimicrobial resistance.

Inclusion Criteria:

• patients with H. pylori infection who had never received treatment for H. pylori infection
• H. pylori infection defined by a positive rapid urease test (CLOtest, Delta West, Bentley, Australia) by gastric mucosal biopsy from the lesser curvature of the mid antrum or mid body or histological evidence of H. pylori by modified Giemsa staining in the lesser and greater curvature of the mid antrum or mid body, respectively or a positive C-urea breath test.

Exclusion Criteria:

• Patients with concurrent critical illness, a history of previous upper gastrointestinal surgery, contraindication to any of the study medications, recent frequent intake of NSAIDs, anticoagulants or steroids, an allergy to the study medications, and those that were pregnant or breast-feeding women were excluded from the study. Other exclusion criteria include recent use of antimicrobials and any condition probably associated with poor compliance such as drug abusers or alcoholics.