Evaluation of ceftazidime concentration released in agar from an E test strip.

The aim of this study was to evaluate, using high-performance liquid chromatography, the concentration of ceftazidime in agar released from an E test strip, sampling at the edge of the strip at different points (1, 2, 4, 8, 16, 32, 64, and 128 μg/ml) at 6, 15, and 24 h after its deposition on uninoculated plates. From 6 to 24 h, the ceftazidime concentration in agar increased at the graduations 1, 2, and 4 μg/ml (+140, +82, and +58%, respectively), remained fairly constant at 8 μg/ml (–1.9%), and decreased at 16, 32, 64, and 128 μg/ml (–25, –44, –36, and –58%, respectively). In the 6–24 h range, the ceftazidime concentrations between 16 and 1 μg/ml were ±1 serial dilution of the values reported on the strip, confirming the accuracy of the E test in agar.