BackgroundWe previously performed a pragmatic cluster randomized controlled trial (RCT) in general practices and older adult care organizations in Poland, the Netherlands, Norway, and Sweden. We found that a multifaceted antibiotic stewardship intervention (ASI) substantially reduced antibiotic use for suspected urinary tract infections (UTIs) in frail older adults compared with usual care. We aimed to evaluate the implementation process of the ASI to provide recommendations for clinical practice.MethodsWe conducted a process evaluation alongside the cluster RCT. The ASI consisted of a decision-tool and a toolbox, which were implemented using a participatory-action-research (PAR) approach with sessions for education and evaluation. We documented the implementation process of the intervention and administered a questionnaire to health care professionals (HCPs) from participating organizations in the intervention and usual care clusters. We evaluated the multiple components of the intervention and its implementation following a structured framework.ResultsThe questionnaire was completed by 254 HCPs from the 38 participating clusters. All components were largely delivered according to plan and evaluated as useful. The decision-tool and toolbox materials were reported to facilitate decision-making on UTIs. Regarding the PAR approach, educational sessions focusing on the distinction between UTIs and asymptomatic bacteriuria were held in all 19 intervention clusters. In 17 out of these 19 clusters, evaluation sessions took place, which were reported to help remind HCPs to implement the ASI. During both sessions, HCPs valued the reflection that took place and the resulting awareness of their behavior. It allowed them to explore implementation barriers and to tailor their local implementation process to overcome these. For example, HCPs organized extra educational sessions or revised local policies to incorporate the use of the decision-tool. Various HCPs took key roles in implementation. Staff changes and the COVID-19 pandemic were important contextual barriers.ConclusionsWe found each component of the multifaceted ASI and its implementation to have added value in the process to improve antibiotic prescribing for suspected UTIs in a heterogeneous older adult care setting. We recommend using a multifaceted, multidisciplinary approach that enables HCPs to reflect on their current practice and accordingly tailor local implementation.Trial registrationClinicalTrials.gov NCT03970356. Registered on May 31, 2019.