How do you decide between ceftolozane/tazobactam and ceftazidime/avibactam for empiric treatment of an infection due to difficult-to-treat Pseudomonas aeruginosa while awaiting additional susceptibilities?

Either is generally acceptable. The choice of empiric therapy in this circumstance may be dependent on additional information, if available. As an example, a patient with cystic fibrosis may have recent microbiological data that could guide the decision. Such information, however, is not often available in other populations and in some cases it may be misleading.

Variable in vitro susceptibility results comparing the two agents are reported, but in many instances show limited differences. In one example, a global collection of 149 carbapenem-resistant P. aeruginosa found 11% and 13% resistant to ceftolozane-tazobactam and ceftazidime-avibactam, respectively (Gill et al., PMID 34291323). In addition, a multicenter retrospective study of pati...

Our institution prefers ceftolozone tazobactam for PSA rather than caz-avi. This is due to data shown above regarding higher rates of clinical success- since both are available to us, we prefer to avoid unnecessary use of caz-avi except for CRE. the only time we use caz avi for PSA is if the patient also has a CRE.