Comparison of the serum bactericidal activity of ceftriaxone/piperacillin and ceftriaxone/netilmicin.

The serum bactericidal activities of ceftriaxone, netilmicin, piperacillin and the combinations of ceftriaxone with each of the two other antibiotics were compared 1, 4 and 24 h after i.v. infusion in six volunteers. One hundred and one clinical isolates were used, includingStaphylococcus aureus, Pseudomonas aeruginosaand variousEnterobacteriaceae.The highest bactericidal titers were found against theEnterobacteriaceae,geometric means of 1 ∶741 and 1∶851 being obtained for ceftriaxone/netilmicin and ceftriaxone/piperacillin respectively. AgainstStaphylococcus aureusthe geometric mean bactericidal titers of ceftriaxone/piperacillin (1∶105) were markedly higher than ceftriaxone/netilmicin (1∶35). Low bactericidal activity was exhibited by all drugs and combinations tested againstPseudomonas aeruginosa;a geometric mean bactericidal titer of 1∶4.6 was achieved. The serum bactericidal activity of the double beta-lactam combinations was found to be at least equal to that of the combination containing a cephalosporin and an aminoglycoside.