Comparison of the activity of cefoperazone, cefuroxime and cefoxitin against Gram-negative bacilli and synergy studies with cefoperazone and ticarcillin.

83% of at least 11 different species of Gram-negative aerobic bacilli, comprising 270 clinical isolates, were inhibited by 3.1 microgram cefoperazone per ml. 55% and 48% were inhibited by 3.1 micrograms/ml of cefuroxime and cefoxitin, respectively. In addition, cefoperazone inhibited 83 of 96 Pseudomonas aeruginosa isolates at a concentration of 6.2 microgram/ml. Cefoperazone/ticarcillin combinations were shown to be synergistic for 47/96 (49%) of Pseudomonas aeruginosa isolates studied, when lowering of the minimum bactericidal concentrations of the 2 drugs was the criterion for enhancement of activity. Cefoperazone/ticarcillin combinations were also shown to be synergistic against 15/30 Serratia marcescens isolates. We discuss the possible advantages of synergistic combinations of drugs of relatively low toxicity, for the management of complicated infections.