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Abstract

Introduction: Pseudomonas aeurginosa (PsA) infections in the intensive care unit (ICU) are becoming more difficult to treat due to increasing resistance. Guidelines recommend that ICU providers examine their own resistance patterns to guide empirical antibiotics. Our empirical therapy for presumed PsA infections is piperacillin/tazobactam (PT) plus a fluoroquinolone (FQ). Unfortunately, traditional antibiograms cannot identify optimal combination therapy; whereas a combination antibiogram shows how frequently an organism is resistant to the first antibiotic but susceptible to the second antibiotic and identifies which combination of antibiotics may be most effective. Hypothesis: Developing a combination antibiogram for PsA will allow identification of the most appropriate empirical antibiotic therapy. Methods: All PsA isolates from respiratory and blood cultures in the surgical ICU between 01/08-12/10 were retrospectively reviewed. Only first isolates were included and susceptibility to each antibiotic was recorded according to Clinical Laboratory Standards Institute criteria and pharmacokinetic-pharmacodynamic derived minimum inhibitory concentration breakpoints. In a matrix fashion, the percentage of isolates susceptible to at least one of two combined agents was listed. Results: Fifty-two PsA isolates were included. 65.3% were susceptible to PT and 78.8% to ceftazidime. Tobramycin improved the antimicrobial susceptibility of PT (100%, p=0.001), ceftazidime (100%, p=0.001), cefepime (75 vs 100%, p=0.001), imipenem (44 vs 98%, p=0.001), and meropenem (53 vs 100%, p=0.001). Gentamicin and amikacin only increased the coverage of imipenem to 65% (p=0.048) and 84% (p=0.001), respectively, but they did not significantly improve other beta-lactam coverage. Ciprofloxacin failed to improve upon any of the beta-lactam susceptibilities. Conclusions: Adding tobramycin as a second antibiotic would likely increase the number of patients receiving optimal empirical therapy for PsA. The use of a combination antibiogram at our institution identified ceftazidime or cefepime plus tobramycin as the most optimal empirical therapy, and that FQ use should be abandoned for empirical treatment of PsA.