Introduction Urinary tract infections (UTIs) are one of the most common reasons for antibiotic use in residential aged care (RAC), yet antibiotic treatment often exceeds recommended durations and underuses first-line agents, increasing harm and antimicrobial resistance. We designed clinical decision support (CDS) embedded in an electronic medication system (BESTMED) to prompt guideline-concordant prescribing. We evaluated the usability of the CDS and its influence on prescribing. Methods The study had two phases: user testing and an evaluation of alerts displayed and prescriber responses in 65 RAC homes. During user testing, prescribers completed think aloud prescribing scenarios and interviews, with feedback used to refine the CDS. The enhanced CDS was implemented from September 2025, and weblog data on alert types and prescriber responses were analysed to assess its effect on prescribing decisions. Results Usability testing (n=5) revealed positive responses, with users valuing the cross-check against guidelines. Resistance to change and time constraints were identified as barriers to the CDS influencing prescribing. Between 1 September 2025 and 18 February 2026, 1517 alerts were displayed to 283 prescribers when ordering 962 antibiotic prescriptions. Of the alerts, 63.7% (n=941) flagged prolonged durations and 36.3% (n=537) non-first-line agents. Following an alert, prescribers selected the option to change their prescription in 32.4% (n=492) of cases; more frequently in response to duration alerts (41.1% of duration alerts) compared with agent alerts (17.9%). Reasons for not changing a prescription included clinical judgement, following another clinician’s or hospital order, and supply delays. Conclusion A CDS alerting prescribers to non-guideline concordant UTI antibiotic orders may improve antibiotic prescribing practices in RAC.