The purpose of this study is to assess and compare the effectiveness of furazolidone-tetracycline-containing and metronidazole-tetracycline-containing quadruple regimens for the rescue treatment of Helicobacter pylori infection inpatients allergic to penicillin.

Helicobacter pylori(H.pylori), which infects about 50% of the global population,has been recognized as a main risk factor of multiple gastric pathologies,especially non-cardiac gastric cancer. Strongly evidence supports that H.pylori eradication is an effective approach to reduce the incidence of those pathologies.However,Helicobacter pylori eradication is a challenge in patients allergic to penicillin. Therefore, the investigators aim to assess and compare the effectiveness of furazolidone-tetracycline-containing and metronidazole-tetracycline-containing quadruple regimens for the rescue treatment of Helicobacter pylori infection in patients allergic to penicillin.

Inclusion Criteria:

• Patients aged 18-70 with H. pylori infection.
• Patients with previous Helicobacter pylori eradication.
• Patients Allergic to Penicillin.

Exclusion Criteria:

• Patients treated with H2-receptor antagonist, PPI, bismuth and antibiotics in the previous 4 weeks.
• Patients with gastrectomy, acute GI bleeding and advanced gastric cancer.
• Patients with known or suspected allergy to study medications.
• Currently pregnant or lactating.
• Inability to provide informed consent and other situations that could interfere with the examination or therapeutic protocol.