Pseudomonas aeruginosa bacteremia: susceptibility of 100 blood culture isolates to seven antimicrobial agents and its clinical significance.

The susceptibility of 100 blood culture isolates of Pseudomonas aeruginosa observed during 4 1/2 years was tested for tobramycin, netilimicin, gentamicin, amikacin, pirbenicillin, ticarcillin and carbenicillin, singly and in combination. For aminoglycosides, the agar MICs were twofold to threefold greater than tube dilution MICs but for the penicillins they were similar. For aminoglycosides and ticarcillin, the MBCs were twofold greater than the tube dilution MICs. The MBCs were not achieved at concentrations as high as 512 micrograms/ml for 40% of the isolates for pirbenicillin and for 10% for carbenicillin. Tobramycin and pirbenicillin had the lowest MICs for the aminoglycosides and penicillins, respectively. Synergism was tested and observed between tobramycin + ticarcillin and amikacin + ticarcillin. No overall increase in resistance to gentamicin or carbenicillin was seen from 1974 to 1977. However, patients given repeated courses of gentamicin had more resistant strains. Following the administration of 1.5 mg/kg/dose of gentamicin, peak serum concentrations failed to achieve the MIC for the microorganism in 22% of the patients. The MIC was achieved in all patients receiving the same dose of tobramycin. The overall fatality rate was 67% with one third of the patients dying within 36 hr. There was no relationship of patient fatality rate and MIC for the microorganism. Although in the rapidly fatal group of all patients receiving inappropriate therapy died, the fatality rates of appropriately or inappropriately treated patients in the ultimately fatal and nonfatal groups were similar. Underlying host disease was the major determining factor in patient survival.