Impact of expired stock on antimicrobial surveillance in rural hospitals: implications and challenges for stewardship

Background: Quantitative surveillance of antimicrobial use is a valuable tool used to support antimicrobial stewardship, identify overprescribing, monitor unexpected changes in usage, and assess the impact of interventions to improve prescribing. Smaller, more remote hospitals face many challenges in conducting effective antimicrobial surveillance. Aim: To investigate the impact of expired stock on reported antimicrobial usage rates in smaller, more remote hospitals. Method: Antimicrobial usage rates (defined daily doses [DDDs] per 1000 occupied bed days [OBDs]) were calculated using monthly dispensing data and hospital activity data from 12 rural South Australian facilities for the period January 2018 to December 2020. Usage rates were re-calculated, excluding expired stock, to estimate the impact expired stock had on reported usage rates and to quantify stock wastage. Results: Between 2018 and 2020, the average monthly aggregate usage rate for all 12 hospitals was 650 DDD/1000 OBDs, with the exclusion of expired stock resulting in an average monthly reduction of 37 DDD/1000 OBDs (5.7%). Analysis by the Australian Institute of Health and Welfare peer group demonstrated that the exclusion of expired stock reduced average monthly usage rates by 6.0% for Public Acute Group C sites and 10.6% for Public Acute Group D and Very Small Hospitals. Conclusion: Replacement of expired stock may account for a substantial proportion of perceived antimicrobial usage in rural and remote hospitals, particularly for agents infrequently prescribed. Pharmacy distribution data is a surrogate measure for actual patient consumption; utilisation reports for smaller rural facilities should be interpreted with acknowledgment of the challenges of stock management in remote locations.