Arbekacin activity against contemporary clinical bacteria isolated from patients hospitalized with pneumonia

Arbekacin is a broad-spectrum aminoglycoside licensed for systemic use in Japan and under clinical development as an inhalation solution in the United States. We evaluated the occurrence of organisms isolated from pneumonias in U.S. hospitalized patients (PHP), including ventilator-associated pneumonia (VAP), and the in vitro activity of arbekacin. Organism frequency was evaluated from a collection of 2,203 bacterial isolates (339 from VAP) consecutively collected from 25 medical centers in 2012 through the SENTRY Antimicrobial Surveillance Program. Arbekacin activity was tested against 904 isolates from PHP collected in 2012 from 62 U.S. medical centers and 303 multidrug-resistant (MDR) organisms collected worldwide in 2009 and 2010 from various infection types. Susceptibility to arbekacin and comparator agents was evaluated by the reference broth microdilution method. The four most common organisms from PHP were Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella spp., and Enterobacter spp. The highest arbekacin MIC among S. aureus isolates from PHP (43% methicillin-resistant S. aureus [MRSA]) was 4 μg/ml. Among P. aeruginosa isolates from PHP, only one had an arbekacin MIC of >16 μg/ml (MIC50 and MIC90, 1 and 4 μg/ml), and susceptibility rates for gentamicin, tobramycin, and amikacin were 88.0, 90.0, and 98.0%, respectively. Arbekacin (MIC50, 2 μg/ml) and tobramycin (MIC50, 4 μg/ml) were the most potent aminoglycosides tested against Acinetobacter baumannii. Against Enterobacteriaceae from PHP, arbekacin and gentamicin (MIC50 and MIC90, 0.25 to 1 and 1 to 8 μg/ml for both compounds) were generally more potent than tobramycin (MIC50 and MIC90, 0.25 to 2 and 1 to 32 μg/ml) and amikacin (MIC50 and MIC90, 1 to 2 and 2 to 32 μg/ml). Arbekacin also demonstrated potent in vitro activity against a worldwide collection of well-characterized MDR Gram-negative and MRSA strains.