South Korea has the highest incidence of gastric cancer worldwide and Helicobacter pylori infection is still prevalent. Clarithromycin-containing triple therapy is still the primary therapy approved by the Korean government. However, studies of antibiotic resistance has shown that regional resistance pattern to antibiotics such as clarithromycin, metronidazole, or quinolone. Recent study in Korea has shown that modified-quadruple therapy has comparable eradication rate to concomitant therapy. However, there has been no comparable study of modified-quadruple therapy with bismuth-containing quadruple therapy. The aim of this study is to compare the eradication rate of modified-quadruple therapy and bismuth-containing quadruple therapy with presenting phenotypic and genotypic antibiotic resistance profile.

South Korea has the highest incidence of gastric cancer worldwide and Helicobacter pylori infection is still prevalent. Clarithromycin-containing triple therapy is still the primary therapy approved by the Korean government. However, studies of antibiotic resistance has shown that regional resistance pattern to antibiotics such as clarithromycin, metronidazole, or quinolone. Recent study in Korea has shown that modified-quadruple therapy has comparable eradication rate to concomitant therapy. However, this study did not explore the antibiotic resistance profile of Helicobacter pylori. And, there has been no comparable study of modified-quadruple therapy with bismuth-containing quadruple therapy. The aim of this study is to compare the eradication rate of modified-quadruple therapy and bismuth-containing quadruple therapy with presenting phenotypic and genotypic antibiotic resistance profile.

Inclusion Criteria:

• Participants who had upper endoscopic examination within 3 months and diagnosed by Helicobacter pylori infection either by rapid urease test, urea breath test, or histopathologic examination.
• Participants who voluntarily want to participate in this study.

Exclusion Criteria:

• Participants who had history of Helicobacter pylori eradication.
• Participants who had experience of stomach resection.
• Participants who had history of allergy or adverse events related to eradication medication.
• Participants who had history of administration of proton-pump inhibitor within 2 weeks or Histamine 2 receptor blocker within 1 week.
• Participants who had history of administration of these drugs within a week or who need continuous administration of these drugs; aspirin (except low-dose aspirin for primary prophylaxis of cardiovascular disease), intravenous or oral NSAID, anticholinergics, prostaglandin analogs, pro-motility drugs, sucralfate
• Participants who had history of administration of antibiotics within 4 weeks.
• Pregnant, breast feeding participant or who do not have a will to avoid pregnancy during clinical trial
• Participants who are administrating one of these drugs (Lovastatin, Simvastatin, Atorvastatin, Indinavir, Ritonavir, Cyclosporin, Terfenadine, Cisapride, Pimozide, Astemizole, HIV protease inhibitors (Atazanavir, Nelfinavir), Ergotamine, Dihydroergotamine, Mizolastine, Bepridil, Ticagrelor)
• Participants who have infectious mononucleosis, central nervous system infection, hematologic disease, galactose intolerance, Lapp lactase deficiency, glucose-galactose malabsorption, Torsades de pointes.