Relation between flomoxef minimum inhibitory concentrations and clinical outcomes of patients treated with flomoxef for Enterobacteriaceae bacteremia Chen-Hsiang Lee,1 I-Ling Chen,2 Chia-Chin Li,3 Chun-Chih Chien3 1Division of Infectious Diseases, Department of Internal Medicine, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kaohsiung, Taiwan; 2Department of Pharmacy, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan; 3Department of Laboratory Medicine, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan Background: Flomoxef is potentially effective against β-lactamase-producing Enterobacteriaceae because limited clinical data demonstrate its effectiveness against Enterobacteriaceae bloodstream infections (BSIs) based on its minimum inhibitory concentrations (MICs). This study was conducted to determine the optimal breakpoints based on the survival of patients with Enterobacteriaceae BSIs treated with flomoxef.Methods: The 30-day crude mortality rate was analyzed among 224 adults who initiated flomoxef monotherapy for Enterobacteriaceae BSIs at a medical center over a 3-year period, according to the flomoxef MICs of the initial isolates. The outcome was evaluated by classification and regression tree modeling and by logistic regression analysis.Results: The 30-day crude mortality was approximately two fold greater in patients whose isolates had flomoxef MICs of ≥2 mg/L (54.9% [62/113]) than in those with isolates with MICs of ≤1 mg/L (26.1% [29/111]); the differences were significant in bivariate analysis (P