In an 80-bed fee-based retirement home with nursing care, the dispatched-pharmacist has provided prescription recommendations to visiting physicians based on pathogen identification using Gram staining as part of an antimicrobial stewardship program. Thus, we evaluated the effects of pharmacist-supported antimicrobial stewardship. We calculated the total number of all antimicrobials and macrolides, fluoroquinolones, and cephalosporins prescriptions per 100 residents per month at the retirement home from January 2013 to December 2017. Using log-transformed monthly resident numbers with an offset before and after the intervention, we performed Poisson regression analyses that adjusted for monthly mean age. Interrupted time series analyses (ITSA) were conducted to examine the changes in the incidence rate ratios for the baseline and slope before and after the intervention. The total number of all antimicrobial prescriptions per 100 residents per month from 2013 to 2017 was 14.10, 18.51, 10.59, 5.41, and 3.90, respectively. Although there was a significant pre-intervention increase in the total number of all antimicrobial prescriptions, the intervention was followed by a significant decrease. There was also a significant reduction in the slope. ITSA of the changes in the prescription of macrolides and fluoroquinolones showed that there were significant pre-intervention increase and followed by a significant post-intervention decrease in the slope. There was no significant change in cephalosporin prescriptions by the intervention. Our study shows that pharmacist-supported AS can reduce antimicrobial prescriptions in a retirement home. Nevertheless, further studies are needed to collect and analyse more data on similar interventions.