This study describes the creation of a combination antibiogram directed toward Pseudomonas aeruginosa to determine the most appropriate empiric antimicrobial regimen(s).


P aeruginosa isolates were collected from all sites between January 2013 and December 2017 for patients admitted to the PICU. Patients with cystic fibrosis and isolates from the same site and susceptibility pattern obtained within 30 days were excluded. β-Lactam susceptibilities were determined and compared with the addition of an aminoglycoside or fluroquinolone and summarized in a combination antibiogram.


One hundred ninety-nine P aeruginosa isolates were included for analysis. The addition of a second agent to piperacillin-tazobactam was shown to have the most significant improvement among the β-lactams, with 70% susceptibility as monotherapy and increases to above 90% with the addition of an aminoglycoside or fluroquinolone. The addition of an aminoglycoside or fluroquinolone to cefepime and meropenem increased coverage to above 95%. The addition of a second agent was likely to increase susceptibility of a monotherapy backbone; however, as the susceptibility of the first-line agent decreased, the susceptibility of the second agent needed to be higher to achieve a 95% coverage threshold.


Our results support use of a second agent to significantly improve the likelihood of appropriate empiric coverage of P aeruginosa. Use of a combination antibiogram may be more beneficial than a simple antibiogram for units with increasing resistance rates, or for coverage of specific resistant organisms.

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