Purpose: Appropriate antibiotic therapy (AAT) is associated with improved clinical outcomes, yet definitions used to assess AAT vary widely and focus predominantly on in-vitro susceptibility. This contrasts with antimicrobial stewardship (AMS) principles, which emphasize additional factors such as infection focus, dosing, route, and treatment duration. We conducted a scoping review to describe how AAT is defined in clinical research and to examine the association between AAT definitions and patient outcomes.

Methods: We included observational studies published between 2011 and 2021 evaluating the impact of AAT on outcomes in hospitalized adults with bacterial infections. Definitions of empiric and definite AAT were extracted and categorized according to the aspects considered. Association between definition characteristics and reported outcomes were analysed.

Results: Among 288 included studies, nearly all (98.6%) provided a definition of AAT. Most definitions relied on in-vitro susceptibility alone for empiric (40.7%, 105/258) and definite (31.7%, 13/41) therapy. Other aspects (e.g. dosing, duration, guideline adherence) were used inconsistently and with heterogeneous operationalization. Details on AAT assessment were frequently missing for several aspects, including dosing and route of administration. Empiric AAT was associated with improved outcomes in 62.8% (125/199), particularly for long-term and ICU mortality. However, the associations did not differ consistently by the type or complexity of AAT definition, except when minimum treatment duration was included.

Conclusion: AAT definitions in current clinical research remain largely susceptibility-based and incompletely aligned with AMS frameworks. More standardized, multidimensional definitions that incorporate clinical, pharmacological, and stewardship criteria are needed to enable comparability across studies and to better understand the true impact of AAT on patient outcomes.

Keywords: Antibiotic susceptibility; Antimicrobial stewardship; Appropriate antibiotic therapy; Quality indicators; Scoping review.