The purpose of this study is to assess and compare the effectiveness and safety of high-dose dual therapy and half-dose clarithromycin-containing bismuth quadruple therapy in elderly patients for eradicating H.pylori.

Helicobacter pylori plays an important role in many diseases such as peptic ulcer disease and MALT lymphomas. And the prevalence of H. pylori remains high in developing countries,including China.

Clarithromycin-containing bismuth quadruple therapy has been recommended as the first-line therapy for H pylori infection in China. However, its expensive cost and high antibiotic-related adverse reactions are always haunting us. In 2018,a research from NanFang hospital(China）revealed that 250mg clarithromycin is as effective as 500mg clarithromycin，at the same time，causes less adverse reactions. On the othe hand,previous studies reported a new regimen called large dose dual therapy（generally contains a PPI and amoxicillin),while some of them have achieved very good results,especially in Taiwan.

However, specific data on anti-H.pylori treatments in elderly people are very lacking.So,we aim to assess and compare the effectiveness and tolerability of high-dose dual therapy and half-dose clarithromycin-containing bismuth quadruple therapy in elderly patients.Considering the difference of drug metabolism between eldery and young people，a satisfactory result may be obtained.

Inclusion Criteria:

• Patients, aged greater than 65 , with positive H. pylori infection that was not eradicated by previous therapies are included. The H. pylori infection is confirmed by the positive rapid urease test or 13C-breath test.

Exclusion Criteria:

• Patients with significant underlying disease including liver, cardiac, pulmonary, and renal diseases, neoplasia, coagulopathy and genetic diseases, history of gastric surgery, pregnancy, breast-feeding, active gastrointestinal bleeding, the use of PPI, NSAID or antibiotics during the 4 weeks prior to enrolment, and previous history of allergic reactions to any of the medications used in this protocol. Patients previously treated with H. pylori eradication regimens or those unwilling to participate in the study were also excluded.