[In vitro antibacterial activity of cefpirome in combination with 4 aminoglycosides and 2 fluoroquinolones]

Combinations of cefpirome with aminoglycosides (gentamicin, tobramycin, netilmicin, amikacin) and of cefpirome with fluorinated quinolones (pefloxacin, ofloxacin) were tested against 20 Enterobacteriaceae, 6 Pseudomonas aeruginosa, 6 Acinetobacter calcoaceticus, 6 group D Streptococci and 6 Staphylococcus aureus strains, susceptible, intermediate or resistant with a low level to these different compounds. Activity of combinations was evaluated using a broth microdilution checkerboard method and FIC indices determination. Combinations of cefpirome with aminoglycosides demonstrated a synergistic effect in 79.5% of cases, but a strong synergy (FIC less than or equal to 0.62) was observed in only 46% of cases. The higher rate of strong synergy concerned Enterobacteriaceae (50% of cases) and group D Streptococci (58.3%). Combination of cefpirome with gentamicin was the most active against Enterobacteriaceae and with a lower degree against P. aeruginosa, A. calcoaceticus and S. aureus. Combination of cefpirome with netilmicin was the best association against group D Streptococci. Combinations of cefpirome with fluorinated quinolones demonstrated frequently and additive (40.9%) or indifferent (36.3%) effect. When a synergistic effect was proved, it was always weak (FIC = 0.75). Combinations of two fluorinated quinolones with cefpirome gave similar results. No combination was antagonist. This study is a primary estimation of activity of cefpirome combined with other agents. It will be necessary to confirm these results against strains resistant with high level, especially against cefpirome, strains not discovered in clinical isolates at present.