Combination effect of ceftriaxone with four aminoglycosides on nonfermenting gram-negative bacteria.

The in vitro efficacy of ceftriaxone in combination with gentamicin, tobramycin, amikacin and netilmicin against 50 nonfermenting gram-negative bacterial strains was compared by use of the checkerboard agar dilution technique. On average 42.5% of all nonfermenting strains were inhibited by additive, 22.5% by synergistic ceftriaxone-aminoglycoside combinations. Great variations occurred between the different bacterial species. Ceftriaxone-tobramycin interactions were superior to combinations with other aminoglycosides. Ceftriaxone-aminoglycoside combinations were most active on Pseudomonas aeruginosa and least potent on Pseudomonas cepacia.