[In vitro interaction of piperacillin and imipenem/cilastatin combined with aminoglycosides against Pseudomonas aeruginosa].

The in vitro interactions of piperacillin (PIPC) and imipenem/cilastatin (IPM/CS) combined with 5 kinds of aminoglycosides (gentamicin, tobramycin, amikacin (AMK), isepamicin and netilmicin) were investigated against IPM/CS-susceptible (MIC of IPM/CS was < or = 3.13 micrograms/ml) and IPM/CS-resistant (MIC of IPM/CS was > or = 12.5 micrograms/ml) Pseudomonas aeruginosa. The following results were obtained. 1. In the checkerboard dilution studies, the combinations of PIPC with aminoglycosides showed synergistic effect for more than 50% of the each 54 strains of IPM/CS-susceptible and IPM/CS-resistant P. aeruginosa. The synergistic/additive effects of PIPC with aminoglycosides were demonstrated for all tested strains. 2. In the checkerboard dilution studies, the combinations of IPM/CS with aminoglycosides showed no antagonism against any strains. The synergistic effects of IPM/CS with aminoglycosides were demonstrated for 0 to 14.8%, and these values were smaller than the combinations of PIPC with aminoglycosides. 3. Corresponding to the results of checkerboard dilution studies, the combination of PIPC with AMK was more effective than the combination of IPM/CS with AMK on the killing curve for IPM-resistant P. aeruginosa. In conclusion, PIPC showed the synergistic effects in combinations with aminoglycosides against IPM/CS-resistant P. aeruginosa. These results suggest that the combination therapies of PIPC with aminoglycosides are useful for the clinical treatment of serious infections due to P. aeruginosa.