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79 Effect of Piperacillin/Tazobactam (P/T) De-restriction on Antibiotic Usage and Susceptibility of Pseudomonas aeruginosa Isolates

Saturday, April 2, 2011
Trinity Ballroom (Hilton Anatole)
Jennifer Christoff Pisano, MD , University of Chicago Medical Center, Chicago, IL
Ryan Dunn, MD , University of Chicago Medical Center, Chicago, IL
Benjamin Brielmaier, PharmD , University of Chicago Medical Center, Chicago, IL
Armand M. Ryden, MD , UCLA David Geffen School of Medicine, Los Angeles, CA
Emily Landon Mawdsley, MD , University of Chicago Medical Center, Chicago, IL
Stephen G. Weber, MD, MSc , University of Chicago Medical Center, Chicago, IL

Background: Antibiotic restriction through pre-approval is commonly used to regulate antibiotic utilization and control cost but has not been consistently shown to affect antibiotic resistance.  Little is known about the effect of de-restriction of a previously restricted antibiotic on antimicrobial resistance and antibiotic utilization.

Objective: To examine the effects of the de-restriction of P/T on P/T utilization and on the antimicrobial resistance and MIC distribution of P. aeruginosa isolates to P/T.

Methods: De-restriction of P/T at a university hospital occurred in July 2007.  A retrospective analysis of all VITEK2-available P. aeruginosa MIC data from a total of 768 isolates (375 isolates before and 393 isolates after de-restriction) and P/T utilization for patients >18y admitted to inpatient services for the year before and after de-restriction was performed.  The number of unique patients receiving P/T per 100 admissions, days of therapy (DOT) per 1000 patient days, modal MIC and MIC distribution for P. aeruginosa before and after de-restriction were compared.

Results: Overall, there was a significant increase in P/T use after de-restriction (Fig): 108 DOT/1000 patient-days (13,277 total DOT/122,888 patient-days) before de-restriction versus 147 DOT/1000 patient-days (16,833 DOT/114,350 patient-days) after de-restriction, p<0.001.  There were 9.5 P/T starts per 100 admissions before and 12.0 after de-restriction, p<0.001.   The modal MIC for both time periods was 4, and accounted for 48% (pre) and 46%(post) of the total isolates.   The geometric mean for MIC distribution before de-restriction was 10.0 and after de-restriction was 9.8.  There was no significant difference in MIC distribution using the Wilcoxon rank sum test.  Overall, the percentage of susceptible P. aeruginosa isolates to P/T was 94% in the years before and after de-restriction.

Conclusions: De-restriction of P/T resulted in an increase in overall P/T utilization; however, the resistance and MIC distribution for P. aeruginosa isolates did not change in the first year of unrestricted use.  These results suggest that de-restriction of antibiotics may not increase antibiotic resistance in the short term, although, subsequent changes in bacterial resistance and MIC distribution may take longer to develop.  Further study is needed to examine the impact over time or on other bacterial species.