Bactericidal activity of cephalosporins in an in vitro model simulating serum levels.

The bactericidal activity of cefazolin, cephaloridine, and cephalothin in a simulated intramuscular study (500 mg) and a simulated intravenous drip infusion study (2 g/2 h) is reported. In both model systems, the bactericidal activity of cefazolin surpassed that of cephalothin, and there were certain differences between cefazolin and cephaloridine in the simulated intramuscular study when human serum was used as a medium. In a routine reference static system, the drug levels were constant at the simulated peak level of each cephalosporin by both routes. In this system the three cephalosporins were equal in activity. In a third experiment, the effect of drug concentrations and exposure time on bactericidal activity of the cephalosporins was studied. The bactericidal activity of cephaloridine was the strongest of the three drugs when exposure time was 2 h and drug concentration was less than four times the minimal inhibitory concentration. At concentrations above four times the minimum inhibitory concentration, all three cephalosporins were equal in activity when the exposure time was 2 h.