Amoxicillin Resistance in Helicobacter pylori: Studies from Tokyo, Japan from 1985 to 2003

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Abstract
Background.  Previous reports revealed no resistant strains of amoxicillin (AMPC), which is usually used in eradication therapy for H. pylori infection. However, the frequency and evolution of natural AMPC‐resistant strains in the Japanese population remains unknown.Aim.  To assess the prevalence of H. pylori resistance against AMPC in the Tokyo area, a collection of 648 H. pylori strains isolated from patients with GI diseases from 1985 to 2003 was tested for their sensitivity to AMPC.Methods.  The susceptibility of the strains was assessed by determination of the minimal inhibitory concentration (MIC) using the E‐test and/or the Dry‐plate method. The susceptibility breakpoints of AMPC for H. pylori were: sensitive (AMPC‐S); MIC < 0.04 µg/ml, intermittent resistance (AMPC‐I); 0.04–1, resistant (AMPC‐R); > 1.Results.  No AMPC‐R strains were detected in the strains isolated between 1985 and 1996, while the rate of resistance was determined to be 1.1%, 2.1%, 5.4%, 5.6%, 0%, 8.8%, and 1.5% every year, respectively, from 1997 to 2003. The percentage of AMPC‐I strains increased from 2000 to 2003. The total eradication rate of H. pylori in the patients who received triple therapy containing AMPC was 81.4% (214/263). Classified as above, the rates of AMPC‐S, AMPC‐I, and AMPC‐R were 84.6%, 77.8%, 25%, respectively.Conclusion.  H. pylori resistance to AMPC is still rare in Japan, although the percentage of AMPC‐I strains has increased over the last 4 years. The frequency of isolation of strains showing true resistance to AMPC may increase in the future, along with an increase in the frequency of isolation of AMPC‐I strains.

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