Role of pH in the lethal direct cell damaging action of miconazole.

Experiments with Candida albicans showed that the direct cell-damaging lethal action of miconazole is operative against log-phase cells at pH 7.0 but not at pH 5.5. Cultivation at pH 5.5 without miconazole did not inhibit development of susceptibility to miconazole kill, but killing itself was prevented at pH 5.5. It is suggested that non-protonated neutral drug molecules are required for direct lethal miconazole action.