[Basic studies on combination effects of arbekacin and beta-lactam antibiotics on methicillin-resistant...

Combination effects were studied with arbekacin (ABK) and beta-lactam antibiotics including imipenem/cilastatin (IPM/CS), flomoxef (FMOX), and cefotiam (CTM) for bactericidal activities, post-antibiotic effects (PAE's) and bactericidal activities of beta-lactam antibiotics after removal of ABK using methicillin-resistant Staphylococcus aureus (MRSA) strain 1936. The following results were obtained. 1. When ABK was administered in combination with IPM/CS, FMOX or CTM against MRSA strain 1936, low FIC index was not obtained. 2. Higher bactericidal activity was observed when ABK was given before beta-lactam than when beta-lactam was given before ABK. 3. Combination of ABK and each of beta-lactam antibiotic led a longer PAE than ABK alone. 4. When each beta-lactam antibiotic was administered after a treatment and removal of ABK, greater bactericidal activity and growth inhibition were observed than when administered each beta-lactam alone. These findings basically demonstrated that ABK was effectively bactericidal against MRSA when administered in combination with beta-lactam antibiotic such as IPM/CS, FMOX or CTM, even when the FIC index did not indicate a favorable effect.