Effect of pH on the activity of ceftizoxime.

The in vitro antibacterial activity of ceftizoxime (Cefizox) is influenced by the ambient pH of the medium. This pH-dependent activity was observed when either the assay discs or the assay medium were buffered. For the conventional disc agar-diffusion assay, using Bacillus subtilis ATCC 6633, the medium buffered to pH 6 had definite advantage for measuring potency and activity. In serial dilution assay, the acidic (pH 6) medium gives better MIC values with Staphylococcus aureus strains. In the case of Escherichia coli strains, the pH of the medium (6, 7.3 and 8) appears to be of less significance.