More than half of the world's population is infected with Helicobacter pylori, a bacterium that colonizes the human stomach. Although most infected subjects live free of symptoms and disease outcomes (except superficial gastritis), only a few develop peptic ulcers or gastric cancer, while some others may develop non-ulcer dyspepsia. Current clinical practice for the management of peptic ulcer disease includes testing for and treating H. pylori, if present. Although there are triple therapies that contain 2 antibiotics plus a bismuth compound, a proton-pump inhibitor, or a H2-receptor antagonist which are effective at eliminating H. pylori in Europe and North America, these treatments are dramatically less effective in developing countries. Our recent meta-analysis showed quadruple therapies containing clarithromycin, amoxicillin, metronidazole and a proton pump inhibitor to be effective in the presence of clarithromycin or metronidazole resistance. However, this regimen has yet to be tested in a developing country. Therefore, in the current randomized clinical trial in Pasto, Colombia, we aim to examine the effectiveness of clarithromycin, amoxicillin, metronidazole with and without a proton pump inhibitor compared to the Food and Drug Administration approved 10-day regimen containing clarithromycin, amoxicillin and omeprazole. Since antibiotic therapy is most effective within a specific gastric pH range, and since mutifocal atrophy results in damage and loss of the acid producing parietal cells, we will test the efficacy of our modified therapy stratified by diagnosis of multifocal atrophic gastritis.