Relationship between the Minimum Inhibitory Concentration of Carbapenems and the Clinical Outcome of Patients with Acinetobacter Bacteremia: A Multicenter Study [PublishAheadOfPrint]

The Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) offer different recommendations for carbapenem minimal inhibitory concentration (MIC) susceptibility breakpoints for Acinetobacter spp. In addition, the clinical efficacy of the intermediate category remains uncertain. This study was designed to determine the optimal predictive breakpoints based on survival of patients with Acinetobacter bacteremia treated with a carbapenem. We analyzed the thirty-day mortality rates of 224 adults who received initial carbapenem monotherapy for treatment of Acinetobacter bacteremia at 4 medical centers over a 5-year period according to the carbapenem MICs of the initial isolates. The thirty-day mortality was about 2-fold greater in patients whose isolates had carbapenem MICs ≥8 mg/L than those with ≤4 mg/L. The differences were significant by bivariate analysis (53.1% [60/113] vs. 25.2% [28/111]; P < 0.001) and on survival analysis by the log-rank test (P < 0.001). Classification and regression tree analysis revealed a split between MICs of 4 and 8 mg/L and predicted the same difference in mortality, P < 0.001. Carbapenem treatment for Acinetobacter bacteremia caused by isolates with carbapenem MICs ≥8 mg/L was an independent predictor of 30-day mortality (odds ratio, 4.218; 95% confidence interval, 2.213--8.039; P < 0.001). This study revealed that patients with Acinetobacter bacteremia treated with a carbapenem had a more favorable outcome when the carbapenem MICs of their isolates were ≤4 mg/L compared to those isolates with MIC ≥8 mg/L.

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