Four weeks after the treatment period (with no administration of PPIs or any antibiotics), we will confirm H. pylori eradication using C13-UBT by a staff member who will be blind to the eradication arm of each patient. In case of treatment failure, a repeated endoscopy will be performed with biopsy specimens being taken (two from the antrum and two from the body of the stomach). Biopsy specimens will be cultured and antibiotic susceptibility will be determined for amoxicillin, tetracycline, clarithromycin, metronidazole, and levofloxacin with the aid of the agar dilution test, according to the standard European protocol.14,15 The microbiologist who will be performing the agar dilution test will be blinded to the treatment. If first-line eradication therapy fails, second-line therapy will be administered, according to antibiotic susceptibility.