In Vitro Comparison of Ceftolozane-Tazobactam to Traditional Beta-Lactams and Ceftolozane-Tazobactam as an Alternative to Combination Antimicrobial Therapy for Pseudomonas aeruginosa

Guidelines for the treatment of sepsis, febrile neutropenia, and hospitala-cquired pneumonia caused by Pseudomonas aeruginosa include empirical regimens incorporating two antibiotics from different classes with activity against P. aeruginosa for select at-risk patients to increase the likelihood that the organism will be susceptible to at least one agent. The activity against P. aeruginosa and the rates of cross-resistance of ceftolozane-tazobactam were compared to those of the beta-lactam comparators cefepime, ceftazidime, piperacillin-tazobactam, and meropenem alone and cumulatively with ciprofloxacin or tobramycin. Nonurine P. aeruginosa isolates were collected from adult inpatients at 44 geographically diverse U.S. hospitals. MICs were determined using reference broth microdilution methods. Of the 1,257 isolates collected, 29% were from patients in intensive care units and 39% were from respiratory sites. The overall rate of susceptibility to ceftolozane-tazobactam was high at 97%, whereas it was 72 to 76% for cefepime, ceftazidime, piperacillin-tazobactam, and meropenem. The rate of nonsusceptibility to all four comparator beta-lactams was 11%; of the isolates nonsusceptible to the four comparator beta-lactams, 80% remained susceptible to ceftolozane-tazobactam. Among the isolates nonsusceptible to the tested beta-lactam comparators, less than half were susceptible to ciprofloxacin. By comparison, approximately 80% of the beta-lactam-nonsusceptible isolates were susceptible to tobramycin, for overall cumulative susceptibility rates of 94 to 95%, nearly 10% higher than that of the ciprofloxacin-beta-lactam combinations and approaching that of ceftolozane-tazobactam as a single agent. The rates of susceptibility to ceftolozane-tazobactam were consistently high, with little observable cross-resistance. Ceftolozane-tazobactam monotherapy performed at or above the level of commonly utilized combination therapies on the basis of in vitro susceptibilities. Ceftolozane-tazobactam should be considered for use in patients at high risk for resistant P. aeruginosa infection and as an alternative to empirical combination therapy, especially for patients unable to tolerate aminoglycosides.