Impact evaluation of a Prescription Search Support (PSS) for antimicrobials: protocol for a stepped-wedge cluster randomised trial in Belgian primary care.

introductionInappropriate antibiotic prescribing in primary care remains a major driver of antimicrobial resistance, despite national guidelines and audit-and-feedback systems. Digital antimicrobial stewardship tools may support clinicians in making evidence-based prescribing decisions. The Prescription Search Support (PSS) tool translates guideline recommendations into an interactive decision tree integrated into electronic health records (EHR). This project aims to evaluate the impact of implementing the tool on antibiotic prescribing behaviour in Belgian general practice and to understand the contextual factors influencing its adoption. METHODS AND ANALYSIS: This stepped-wedge cluster randomised trial includes four steps over 12 months. Belgian general practices were randomised in a 1:3:3:3 ratio using stratified block randomisation. All practices start in the control condition, where physicians are expected to provide usual care. At each step, one cluster transitions to the intervention, where PSS becomes accessible through the EHR. The primary objective is to assess whether the implementation of the tool reduces practice-level antibiotic prescribing rates. The primary analysis will use generalised linear mixed models with a logit link, accounting for clustering, time effects and relevant covariates. Secondary analyses include subgroup analyses by region, EHR vendor and intensity of tool use. A nested process evaluation, combining user log file analysis and semistructured interviews, will assess usability, acceptability, fidelity and mechanisms of impact. Sample size calculations indicate that at least 36-48 practices are required to detect a 5% absolute reduction in prescribing with 80% power. All quantitative analyses will be performed in R, and qualitative data will be analysed using reflexive thematic analysis. ETHICS AND DISSEMINATION: The study will be conducted in compliance with the principles of the Declaration of Helsinki (current version) and the principles of Good Clinical Practice and in accordance with all applicable regulatory requirements. Ethics approval for this study was obtained on 10 October 2025 from the Ethical Committee Research UZ/KU Leuven under reference MP037810. We will ensure that the findings of the study will be disseminated to relevant stakeholders beyond the scientific world including the public, healthcare providers and policy makers. The process evaluation that is part of this trial will inform the further implementation strategy. It will be essential to educate physicians on using this new PSS tool in daily practice. TRIAL REGISTRATION NUMBER: NCT07347015.