Comparison of amikacin and gentamicin.

The sensitivity to gentamicin (G) and to amikacin (A) of 25 strains of Escherichia coli (EC), 25 Klebsiella sp. (K), 25 Proteus and Providence sp. (PP), and 25 Ps. aeruginosa (PA) were tested in vitro by the disc method, by the inocula-replicating method, and by a tube dilution technique using 10-5 microorganisms/ml. Bactericidal concentrations active on 50% and 90% of the strains were 1.5 and 4.5 mug/ml for EC, 3 and mug/ml for K, 1.5 and 3 mug/ml for PP, and 3 and 3 mug/ml for PA. Resistance to killing by 12 mug/ml of G was found for 16 strains (1 EC, 9 K, 4 PP, and 2 PA) but only 5 strains were also resistant to 12 mug/ml of A. Conversely, 4 strains (1 EC, 1 PP, and 2 PA) were resistant to 12 mug/ml of A but were killed by 6 mug/ml of G or even less. G (1.5 MG/KG) AND A (5 mg/kg) were administered to 5 bolunteers in a crossover fashion. The mean bactericidal activity of the sera obtained at 1 hr after the injection of G and A was, respectively, 1/4 and 1/4 for ED, 1/4 and 1/8 for K, 1/2 and 1/2 for PP, and 1/2 and 1/2 for PA. Sera obtained in A-treated patients killed at a dilution of 1/8, 8 strains of ED, 17 K, 1 PP, and O PA; at that dilution sera from G-treated patients killed 5 ED, 9 K, O P, and O PA. The main advantage of A over G might be the absence of cross-resistance between A and G for particular pathogens.