Comparative study of the serum bactericidal activity of cefoperazone alone and in combination with amikacin or mezlocillin against gram-negative bacilli and Staphylococcus aureus.

Serum bactericidal activity (SBA) was studied in vitro after intravenous administration of cefoperazone alone or in combination with mezlocillin or amikacin to human volunteers. One hour after the infusion, cefoperazone (2 g), cefoperazone + mezlocillin (5 g) and cefoperazone + amikacin (500 mg) achieved comparable activity against Escherichia coli and Klebsiella pneumoniae (100% of the strains being killed by a 1:8 or greater dilution). The activity of the three regimens was also similar against Pseudomonas aeruginosa (87-96% of the sera had an SBA greater than or equal to 1:8) and somewhat less for Staphylococcus aureus (52-60% with SBA greater than or equal to 1:8). Six and ten hours after administration, the SBAs were much lower for all regimens; a small advantage for cefoperazone + mezlocillin against K. pneumoniae could be shown in comparison to the other regimens.