Assessment of Susceptibility, Pharmacodynamics, and Therapeutic Response for Interpretation of Piperacillin-Tazobactam in Vitro Activity in the Treatment of Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa remains an important pathogen. Our purpose was to determine the minimum inhibitory con-centration (MIC) and pharmacodynamic (PD) parameters predicting a positive response to therapy with piperacil-lin-tazobactam. Medical records were retrospectively reviewed at 3 centers. Data were recorded to assess age, type of disease, renal function, weight (body mass), MIC, antimicrobial treatment, and clinical outcome. Success was response to piperacillin-tazobactam alone, or in combination with another active agent; failure was lack of response. Of 78 eva-luable patients, 63 responded (7 UTI; 56 non-UTI) and 15 did not; 26 responding received combination therapy and 37 monotherapy. Piperacillin-tazobactam treatment was successful in 53 of 63 of non-UTI disease with a MIC of ≤64/4 μg/mL, but in only 3 of 7 with a MIC of >64/4 μg/mL (P = 0.023); overall 9 of 10 infections by strains with MICs = 32 - 64 μg/mL had a successful outcome. Piperacillin estimated time above MIC at 20% separated those responding from those that did not (P = 0.019).