Helicobacter pylori isolated from patients who later failed H. pylori eradication triple therapy readily develop resistance to clarithromycin.

In this study, the ease of selection of clarithromycin resistance was investigated in clarithromycin-susceptible Helicobacter pylori strains isolated from patients with H. pylori infection prior to the administration of triple-combination eradication therapy (clarithromycin plus amoxicillin plus a proton pump inhibitor). Clarithromycin-susceptible strains isolated from ten patients in whom the eradication therapy was successful and from six patients in whom the eradication therapy was unsuccessful were exposed serially to subinhibitory concentrations of clarithromycin. The number of transfers required for the MICs of the strains to increase by 8- and 32-fold were 6.6 and 7.2, respectively, in the successful eradication group, and as few as 2.4 and 1.5, respectively, in the unsuccessful eradication group. The number of transfers required for the A2142G or A2143G point mutation of the 23S rRNA gene to be detected in the strains were 5 and 8, respectively, for the strains in the successful eradication group, and 1 and 2, respectively, for the strains in the unsuccessful eradication group. These results suggest that patients in the unsuccessful eradication group were infected with strains of H. pylori that readily became resistant to clarithromycin on exposure to the drug.