Third generation oral cephalosporins: comparative in vitro kinetics.

In order to provide additional data on the in vitro antibacterial activity of cefetamet-pivoxil against respiratory pathogens, we determined the bactericidal kinetics of this antibiotic in comparison to cefixime and ceftibuten against H. influenzae, M. catarrhalis, K. pneumoniae, E. coli, S. pneumoniae and S. pyogenes. time-kill studies were performed by using concentrations equal to a x MIC, and 4 x MIC of the antibiotics tested and different inocula (10(5), 10(7) and 10(9) CFU/ml). The strains were incubated in a shaking incubator at 37 degrees C and 1 ml samples were removed at regular intervals for viable count determination. The antibiotics were eliminated by serial ten-fold dilutions in physiological saline before plating. At 4 x MIC of cefetamet and at 10(5) CFU/ml inoculum the results were 99.9% killing or more of H. influenzae and M. catarrhalis at 4 h, and of E. coli and K. pneumoniae within 4 to 6 h, and of E. coli and K. pneumoniae within 4 to 6 h. At the same concentration of MIC and with the same inoculum a 99.9% reduction was achieved against S. pneumoniae within 4 h and against S. pyogenes within 2 h with no regrowth at 24 h in both cases. Similar results were obtained using 10(7) and 10(9) CFU/ml inocula. Cefetamet had efficient killing activity even at lower concentrations. Bactericidal kinetics of cefetamet favorably compare with those of cefixime and ceftibuten. The efficient bactericidal activity of cefetamet-pivoxil indicates a clinical role for this new oral cephalosporin in the treatment of respiratory tract infections.