Piperacillin (T-1220), a new semisynthetic penicillin: in vitro antimicrobial activity comparison with carbenicillin, ticarcillin, ampicillin, cephalothin, cefamandole and cefoxitin.

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Abstract
Piperacillin (T-1220) is a new semisynthetic penicillin with an unusually broad spectrum of antimicrobial activity. In vitro comparisons of this drug with 6 other .beta.-lactam antimicrobics (ticarcillin, carbenicillin, ampicillin, cephalothin, cefamandole and cefoxitin) were conducted. Thse included minimal inhibitory concentrations (MIC) against 394 bacterial isolates, the minimal lethal concentrations (MLC) against 79 of those, and the effect of inoculum size on the MIC and MLC of the drugs. Piperacillin had significantly greater activity than did the other penicillins against Pseudomonas spp. and Klebsiella pneumoniae. Against P. aeruginosa piperacillin was 8- and 16-fold more active than ticarcillin and carbenicillin, respectively. The MLC of piperacillin rarely differed from the MIC by more than 1 log2 dilutions except against P. aeruginosa in which the MLC was 4-fold greater or more than the MIC of 45% of isolates tested. Ticarcillin, carbenicillin and cefoxitin showed minimal inoculum size effects. Cefamandole results showed the greater inoculum size variation with 55% and 37% of isolates showing an 8-fold increase in MIC and MLC respectively by increasing inoculum from 105 to 107 CFU/ml. Piperacillin was intermediately effected having 25% of strains > 8-fold increase in MIC.