Early synergistic interaction between semisynthetic penicillins and aminoglycosidic aminocyclitols against Enterobacteriaceae.

Time-kill curves were used to assess the relative in vitro efficacy of the early interaction of three semisynthetic penicillins with two aminoglycosides against 48 Enterobacteriaceae strains. The most efficacious combinations were piperacillin plus amikacin, which demonstrated synergism (greater than or equal to 2 logs of increased kill after 7 h of incubation) against 43 of 48 (90%) strains, and piperacillin plus gentamicin, which exhibited synergism against 25 of 48 (52%) strains. With the combinations of carbenicillin or ticarcillin plus amikacin or gentamicin, early synergistic killing was demonstrated against only 12 to 29% of the strains.