Dose optimization of piperacillin/tazobactam, cefepime, and ceftazidime for carbapenem-resistant Pseudomonas aeruginosa isolates in Türkiye.

Introduction: Although CRPA may test susceptible to other β-lactams such as ceftazidime (CAZ), cefepime (FEP), and piperacillin/tazobactam (TZP), reduced potency has been observed. We assessed the adequacy of EUCAST Susceptible (S) or Susceptible Increased Exposure (SIE)/(I) doses for CAZ, FEP, and TZP against CRPA clinical isolates.

Methods: CRPA isolates were collected from patients at three Turkish hospitals. CAZ, FEP, and TZP MICs were determined using broth microdilution. Monte Carlo simulations were performed to determine the probability of target attainment (PTA) for a free time above the MIC (fT > MIC) targets for various doses of each agent against isolates defined as susceptible. fT > MIC targets were 70% for CAZ or FEP and 50% for TZP. Cumulative fraction of response (CFR) was calculated. Optimal PTA and CFR was 90% target achievement.

Results: The percentages of isolates SIE/I to CAZ, FEP, and TZP were 49,8%, 47%, and 31,8% respectively. Reduced potency was noted with 54,1% of CAZ-S isolates having MICs of 4 or 8 mg/L. Of the FEP and TZP-S isolates, MICs at the breakpoint (8 and 16 mg/L, respectively) were the mode with 45,2 and 53,9% of isolates for each, respectively. At an MIC of 8 mg/L for CAZ, the EUCAST standard dose was insufficient (CFR of 85%). 3 h infusions of EUCAST SIE doses were required for 90% PTA at MIC of 8 mg/L and an optimized CFR of 100%. For FEP, the SIE dose of 2 g q8h 0.5 h infusion of was effective (CFR 96%), utilization of an extended 3 h infusion further optimized the PTA at 8 mg/L (CFR 99%). For TZP, the standard dose of 4.5 q6h administered as a 0.5 h infusion was inadequate (CFR 86%). A standard TZP dose with an extended infusion (4.5 g q8h over 4 h) and the SIE dose 4.5 g q6h 3 h infusion resulted in CFRs > 95%.

Conclusion: These data support the EUCAST SIE breakpoints for FEP and TZP. To optimize PTA at the SIE breakpoint for CAZ, prolonged infusion is required.