Bactericidal activity of arbekacin against methicillin-resistant Staphylococcus aureus. Comparison with that of vancomycin.

Bactericidal activity of arbekacin (ABK) against methicillin-resistant Staphylococcus aureus (MRSA) was compared with that of vancomycin (VCM). MIC80 of VCM against 1,056 clinical isolates was 2 micrograms/ml and not a single strain of those in which MIC above 4 micrograms/ml was detected. Whereas MIC80 of ABK against the isolates was 1 microgram/ml, but a few strains of which showed MIC of 8 micrograms/ml or 16 micrograms/ml. A killing-curve study indicated that bactericidal activity of ABK was critically dependent on its concentrations. ABK, at higher concentrations, showed excellent killing effects against all the tested isolates, and the effects were superior to those of VCM because of following reasons; great reduction CFU was attained within short time incubation, and the effects were not remarkably influenced by different inoculum sizes of MRSA. At lower concentrations of ABK, between a half and four times MIC, the re-increase of CFU of MRSA with appearance of characteristic small colonies was observed. Considering the concentration of ABK in usual dose, the significance of the re-growth should be carefully assessed. It showed be recommended that the peak concentration of ABK be elevated to higher level if adverse effects do not appear.