Susceptibility of Helicobacter pylori isolates to metronidazole, clarithromycin and amoxycillin in vitro and in clinical treatment in Japan

Background: Primary and acquired resistance to antibiotics is an important factor in determining the reason for treatment failure in Helicobacter pylori infection. We examined the relationship between the susceptibility of H. pylori isolates and the efficacy of chemotherapy. Methods: The minimal inhibitory concentrations (MICs) of metronidazole (MNZ), clarithromycin (CLAR) and amoxycillin (AMOX) of 320 H. pylori pre-treatment isolates were determined by the agar dilution method. In 290 patients with peptic ulcers, H. pylori infection was treated by dual or triple combination therapies for 2 weeks: one proton pump inhibitor (30 mg/day lansoprazole or 20 mg/day omeprazole) and one or two antibiotics (500 mg AMOX. 200 mg CLAR or 250 mg MNZ twice a day). MICs were also determined after the treatment failure. Results: Among the drugs tested, for MNZ and CLAR, 8.1% and 9.1% of the isolates, respectively, were resistant, while no isolate was resistant to AMOX. After unsuccessful treatment using MNZ and CLAR, 66.7% and 70.6% of the isolates changed from sensitive to resistant, respectively. All isolates were sensitive to AMOX after treatment failure. Conclusions: The failure of the H, pylori treatment results in the induction of resistance to CLAR and/or MNZ. Regimens with a high cure rate should be used in order to prevent the generation of acquired resistance to antibiotics.