INTRODUCTIONUp to now, four regimens have generally been used for the eradication of Helicobacter pylori; namely, a bismuthbased triple therapy, a dual therapy consisting of omeprazole plus amoxycillin or clarithromycin, a standard triple therapy consisting of proton pump inhibitor and two antibiotics, either clarithromycin and metronidazole or amoxycillin, and a quadruple therapy 1 consisting of proton pump inhibitor plus bismuth based triple therapy. As in any other infectious disease it is essential in treatment studies of H. pylori infection to stratify the SUMMARY Background: There have been no reports concerning the ef®cacy and safety of a 1-week quadruple therapy regimen of omeprazole, amoxycillin, roxithromycin and metronidazole for Helicobacter pylori infections and the impact of primary resistance on the eradication rate. Methods: One hundred and sixty-nine consecutive patients with peptic ulcer disease as well as gastritis with biopsy-proven H. pylori infection were entered into an open study of omeprazole 20 mg o.m., amoxycillin 500 mg t.d.s., roxithromycin 150 mg b.d., and metronidazole 250 mg t.d.s. Helicobacter pylori status was determined by urease test, histology and culture. Susceptibility to amoxycillin, metronidazole and roxithromycin was determined by the E-test. Results: H. pylori was eradicated in 155 out of 169 (92%; 95% CI 88±96%) by intention-to-treat analysis, and in 155 out of 163 (95%; 95% CI 92±98%) by per protocol analysis. The prevalence of primary resistance against amoxycillin, roxithromycin and metronidazole was 2 out of 166 (1%), 16 out of 166 (10%) and 27 out of 166 (16%), respectively. H. pylori was eradicated in 25 out of 27 (93%) patients with

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