Microdilution antimicrobial susceptibility testing was performed with 73 isolates of Pseudomonas cepacia collected from the sputum of patients throughout Michigan with cystic fibrosis. Susceptibility testing was done using new and investigational antibiotics (loracarbef, cefixime, cefpirome, desacetylcefotaxime, cefpodoxime, cefmetazole, cefepime, cefprozil, and fleroxacin) and commonly used antibiotics (ceftazidime, mezlocillin, piperacillin, ciprofloxacin, tobramycin, and amikacin). Ceftazidime was the most active antibiotic, and 91.8% of isolates were susceptible to it with MIC₅₀ and MIC₉₀ values of ≤4 and 16 μg/ml, respectively. For mezlocillin, piperacillin, and ciprofloxacin 84.9, 89 and 39.7% of the isolates, respectively, were mostly moderately susceptible. Loracarbef, cefixime, cefprozil, cefmetazole, cefepime, fleroxacin, cefpodoxime, tobramycin, and amikacin did not show activity against P. cepacia. For cefpirome and desacetylcefotaxime 24.7 and 60.3% of the isolates, respectively, were moderately susceptible. Both MIC₅₀ and MIC₉₀ were > 32 μg/ml for cefpirome and 32 and > 64 μg/ml for desacetylcefotaxime.

In this study, the antimicrobial activity of several new antibiotics was evaluated using microdilution antimicrobial susceptibility testing against 220 clinically significant isolates obtained from a community hospital. The following antibiotics were studied: loracarbef, cefixime, cefpirome, desacetylcefotaxime, cefpodoxime, cefmetazole, cefepime, cefprozil and fleroxacin. The synergy of two particular drug combinations was evaluated using cefpirome/desacetylcefotaxime and cefpodoxime/ desacetylcefotaxime. Cefpirome was clearly the most active antibiotic: 88% of the isolates tested were found to be susceptible. Specifically, this included 89% of enterococci, 84% of Pseudomonas aeruginosa, and 33% of Pseudomonas cepacia. All of the antibiotics tested demonstrated excellent activity against isolates of Escherichia coli and Klebsiella, Proteus and Salmonella species. For the other antimicrobials, 57, 50, 64, 65, 76, 74, and 64% of the isolates were sensitive to loracarbef, cefixime, cefmetazole, cefprozil, fleroxacin, desacetylcefotaxime, and cefpodoxime, respectively. Among the gram-positive species, 88 and 92.5% of the isolates were sensitive to cefprozil and cefpirome, respectively. Cefepime and fleroxacin demonstrated the highest gram-negative activity with 85 and 89%, respectively, of the isolates being sensitive. The results of this study highlighted cefepime and cefpirome, which showed high overall in vitro activity against 79 and 88%, respectively, of the isolates tested.