Objective To examine the relation between annual trends in the antimicrobial susceptibility of Pseudomonas aeruginosa and drug usage, we compared annual changes in the susceptibility rates of P. aeruginosa clinical isolates during a 4-year period and annual trends in the overall usage of antimicrobials during the same period.
Methods We studied annual trends in MIC₉₀/MIC₅₀, antimicrobial use density (AUD), and antimicrobial susceptibility rates based on clinical breakpoints for 150 strains of P. aeruginosa isolated from respiratory specimens at Dokkyo Medical University Hospital from 2005 through 2008.
Results The MIC₉₀/MIC₅₀ of antimicrobials effective against P. aeruginosa in years 2005, 2006, 2007, and 2008 were as follows: imipenem, 32/2, 32/1, 8/2, and 16/1 μg/mL; meropenem, 8/1, 8/1, 4/0.5, and 4/0.5 μg/mL; and biapenem, 16/1, 32/0.5, 4/0.5, and 8/0.5 μg/mL, indicating that susceptibility to carbapenems increased slightly. The MIC₉₀/MIC₅₀ was 4/0.25, 2/0.125, 1/0.125, and 2/0.25 μg/mL for ciprofloxacin, 8/4, 8/4, 4/4, and 8/4 μg/mL for amikacin, 64/16, 64/16, 64/16, and 64/16 μg/mL for sulbactam/cefoperazone, 8/2, 16/2, 32/2, and 8/2 μg/mL for ceftazidime, indicating little change. The AUDs of fourth-generation cephalosporins increased from 2005 to 2008 (16.2, 18.4, 28.0, and 23.0), while the AUDs of carbapenems decreased (25.7, 23.7, 10.9, and 12.5).
Conclusion The decrease in the AUDs of carbapenems was associated with increased susceptibility rates of P. aeruginosa to carbapenem derivatives. A continuous understanding of trends in the resistance of P. aeruginosa and various other pathogens is essential for designing countermeasures against nosocomial infections, including the proper and effective use of antimicrobials.