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

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Abstract
The in vitro susceptibility of 27 clinical isolates ofHelicobacter pylori to erythromycin, clarithromycin, azithromycin and temafloxacin under various pH conditions was evaluated. Clarithromycin (MIC90 0.03 µg/ml) was found to be significantly more active than either erythromycin (MIC90 0.125 µg/ml) or azithromycin (MIC90 0.25 µg/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 µg/ml) remained lower than those of azithromycin (2 µg/ml) and erythromycin (4 µg/ml). No synergism or antagonism was observed with combinations of clarithromycin and temafloxacin at either the neutral or lower pH values.