Cefotaxime stability during in vitro microbiological testing.

Cefotaxime is a broad-spectrum cephalosporin which is metabolized or degraded to less active or inactive metabolites by serum esterases, elevated temperatures, or a pH outside of its stability range. Cefotaxime instability during in vitro microbiological susceptibility tests may lead to an underestimation of the antibacterial activity of the compound. Cefotaxime and desacetylcefotaxime solutions were studied under MIC and serum inhibitory titer testing conditions. Cefotaxime concentrations, as measured by high-performance liquid chromatography, decreased 20 to 30% over the incubation period in various systems tested; the greatest decline occurred in systems containing serum in the media. Changes in the results of microbiological susceptibility tests interpreted after 6 and 18 h of incubation were consistent with changes observed in the high-performance liquid chromatography analysis. This study demonstrates cefotaxime instability under conditions of in vitro microbiological testing.