In vitro activity, synergism, and testing parameters of amikacin, with comparisons to other aminoglycoside...

The activity of the new aminoglycoside antibiotic, amikacin, was evaluated in vitro against 219 clinical bacterial isolates. One hundred eighty-nine of the 219 strains had agar dilution minimal inhibitory concentration values of 8.0 mug/ml or less for amikacin. Comparative agar dilution studies were performed for gentamicin, kanamycin, and tobramycin. Gentamicin was the most active overall, but tobramycin and amikacin also had significant activity against most bacterial groups. The effects of divalent cations on the susceptibility of Pseudomonas aeruginosa to amikacin were evaluated, and the minimal inhibitory concentration values varied sixfold over a range of divalent cation concentrations from 0.2 to 8.75 mg%. The effects of media and inoculum size on disk susceptibility testing with amikacin were also evaluated. In addition, a synergistic interaction between carbenicillin and amikacin against P. aeruginosa was demonstrated. Amikacin appears to be a promising new broad spectrum antimicrobial agent.