In vitro synergistic activities of aminoglycosides and new beta-lactams against multiresistant Pseudomonas aeruginosa.

The in vitro interactions between amikacin, netilmicin, tobramycin, gentamicin, and various antipseudomonal beta-lactams were studied by the agar dilution checkerboard technique against 30 Pseudomonas aeruginosa strains resistant to all tested antibiotics. Amikacin produced more frequent synergy both at the total and clinically applicable level. Among the beta-lactams, clinically relevant synergistic interactions were obtained in the following order: ceftazidime and ceftriaxone greater than moxalactam greater than aztreonam greater than cefotaxime greater than azlocillin greater than cefoperazone greater than cefsulodin greater than carbenicillin.