Effect of pH variation on the susceptibility of Helicobacter pylori to three macrolide antimicrobial agents and temafloxacin.

The in vitro susceptibility of 27 clinical isolates of Helicobacter pylori to erythromycin, clarithromycin, azithromycin and temafloxacin under various pH conditions was evaluated. Clarithromycin (MIC90 0.03 micrograms/ml) was found to be significantly more active than either erythromycin (MIC90 0.125 micrograms/ml) or azithromycin (MIC90 0.25 micrograms/ml) at a neutral pH. Lowering the pH to 5.75 resulted in a loss in efficacy from 8- to 32-fold for all three macrolides studied. The MIC90 of clarithromycin (0.5 micrograms/ml) remained lower than those of azithromycin (2 micrograms/ml) and erythromycin (4 micrograms/ml). No synergism or antagonism was observed with combinations of clarithromycin and temafloxacin at either the neutral or lower pH values.