Definition of Antibiotic Change Event:

The primary outcome in this study was to evaluate the proportion of initial antibiotic prescriptions associated with an antibiotic change event (ACE). ACEs were classified into one of three mutually exclusive categories based on observed provider order patterns, as shown in Figure 1:

Type of antibiotic change event. (A) early discontinuation, (B) class modification and (C) Administration modification.

Class modification ACEs were further classified based on the effects the change had on bacterial spectrum coverage relative to the initial antibiotic (Figure 1). No spectrum change ACEs were identified when the new antibiotic provided the same bacterial spectrum coverage as the initial antibiotic. For example, a switch in treatment from ciprofloxacin to levofloxacin (broad to broad) or from cephalexin to sulfamethoxazole trimethoprim (narrow to narrow) would both be defined as no spectrum change ACEs according to this approach. Spectrum narrowing ACEs were identified when an initial broad-spectrum antibiotic was switched to a narrow-spectrum antibiotic. Conversely, a spectrum broadening ACE was identified when an initial narrow-spectrum antibiotic was replaced with a broad-spectrum antibiotic.

Changes to antibiotics that were administered with a loading dose (e.g., azithromycin), routinely prescribed in a tapering dose (e.g., oral vancomycin) or administered as a one-time dose (e.g., fosfomycin) were not considered a meaningful ACE for the purposes of this study.