Stable Susceptibility to Aminoglycosides in an Age of Low Level, Institutional Use

INTRODUCTION: The use of aminoglycosides has decreased dramatically over several decades in the United States due to the introduction of safer Gram-negative agents. This study was conducted to assess possibly changing aminoglycoside susceptibility rates between 2006 and 2012 and in reference to 1992 use in the context of aminoglycoside use volume. METHODS: Quarterly adult use of amikacin, gentamicin and tobramycin were determined from the Medical University of South Carolina Medical Center, Charleston, South Carolina, USA, pharmacy drug use database and expressed as total aminoglycoside defined daily doses per 1,000 patient days for the years 1992 and 2006 through 2012. Annual susceptibility of Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae, for the years 1992, 2006, and 2008 through 2012 were retrieved from our hospital’s clinical microbiology database (duplicate isolates were excluded). Quarterly and annualized aminoglycoside usage rates were compared to the other years of interest. Likewise, susceptibility rates of the target organisms to each aminoglycoside were also compared across the same timeframe. RESULTS: While total use of aminoglycosides decreased slightly from 1992 to 2006, it increased by about 40% between 2006 and 2008 and then stabilized. Changes in susceptibility rates between 1992 and 2006 were all ≤±9% with the exception of K. pneumoniae susceptibility to amikacin (−17%). Changes in susceptibility from 1992 to 2012 were also all ≤±9%. Tobramycin remained the most active versus P. aeruginosa (% susceptible = 90), while amikacin remained most active versus E. coli and K. pneumoniae (% susceptible = 98 and 98, respectively). CONCLUSION: With low level use of aminoglycosides in our institution over the past 2 decades, the susceptibility of key Gram-negative pathogens has remained relatively stable, preserving these agents as potential alternative therapies as resistance arises to other frequently used antibiotics.