Influence of borderline cefepime MIC on the outcome of cefepime-susceptible Pseudomonas aeruginosa bacteremia treated with a maximal cefepime dose: a hospital-based retrospective study

BACKGROUND: We assessed the influence of current cefepime minimal inhibitory concentration (MIC) breakpoints and the maximal cefepime dose on treatment outcomes in patients with bacteremia caused by cefepime-susceptible Pseudomonas aeruginosa. METHODS: Adult patients hospitalized between July 2010 and June 2014 with a positive blood culture for cefepime-susceptible P. aeruginosa and receipt of cefepime as the primary therapy throughout the course were reviewed. Cefepime Etest(®) MICs and clinical outcomes for P. aeruginosa bacteremia were reviewed to identify the MIC breakpoint influencing treatment outcomes. RESULTS: Of the 90 patients enrolled, 49 (54.4%) were male (mean age = 66.8 years). The mean Acute Physiology and Chronic Health Evaluation II score was 22.01. Sixty patients (66.7%) received a maximal cefepime dose, and the 30-day crude mortality rate was 36.7%. MIC(90) of cefepime for P. aeruginosa was 8 mg/L. The cumulative survival rate at 30 days revealed that a lower cefepime MIC (<4 mg/L) for P. aeruginosa was associated with a higher survival rate than a higher MIC (≥4 mg/L) (72.6% vs. 23.5%, p < 0.0001). A cefepime MIC of ≥4 mg/L and age were independent risk factors for mortality, whereas the maximal cefepime dose was the independent protective factor. The use of a maximal cefepime dose did not improve the outcomes of patients with P. aeruginosa bacteremia at a MIC of ≥4 mg/L. CONCLUSIONS: A cefepime MIC of 4 mg/L may predict an unfavorable outcome among patients with serious infections caused by P. aeruginosa, even the MICs still within the CLSI susceptibility breakpoint.