Inducing capacity and selection of resistant variants of cefpirome (HR 810) in comparison with other beta-lactam compounds.

The inducing capacity of cefpirome (HR 810) and the ability of the compound to select for stable derepressed mutants was determined and compared with those of cefodizime (HR 221), cefotaxime, ceftazidime and cefamandol. Variations in both characteristics between and within species was observed. Overall, cefodizime showed the lowest, cefamandol the highest inducing capacity. Antibiotic resistant variants were isolated from all strains tested at a frequency of around 10(-9). A stable increased enzyme production was found in Pseudomonas aeruginosa after exposure to ceftazidime as well as in the resistant mutants from Enterobacter cloacae after selection with cefpirome, ceftazidime, cefotaxime and cefamandol. In the other resistant mutants the resistance was probably due to changes in permeability. All resistant variants remained relatively susceptible to cefpirome.