How to measure quantitative antibiotic use in order to support antimicrobial stewardship in acute care hospitals: a retrospective observational study

A cornerstone of antimicrobial stewardship programs (ASPs) is monitoring quantitative antibiotic use. Frequently used metrics are defined daily dose (DDD) and days of therapy (DOT). The purpose of this study was (1) to explore for the hospital setting the possibilities of quantitative data retrieval on the level of medical specialty and (2) to describe factors affecting the usability and interpretation of these quantitative metrics. We performed a retrospective observational study, measuring overall systemic antibiotic use at specialty level over a 1-year period, from December 1st 2014 to December 1st 2015, in one university and 13 non-university hospitals in the Netherlands. We distinguished surgical and non-surgical adult specialties. The association between DDDs, calculated from aggregated dispensing data, and DOTs, calculated from patient-level prescription data, was explored descriptively and related to organizational factors, data sources (prescription versus dispensing data), data registration, and data extraction. Twelve hospitals were able to extract dispensing data (DDD), three of which on the level of medical specialty; 13 hospitals were able to extract prescription data (DOT), 11 of which by medical specialty. A large variation in quantitative antibiotic use was found between hospitals and the correlation between DDDs and DOTs at specialty level was low. Differences between hospitals related to organizational factors, data sources, data registration, and data extraction procedures likely contributed to the variation in quantitative use and the low correlation between DDDs and DOTs. The differences in healthcare organization, data sources, data registration, and data extraction procedures contributed to the variation in reported quantitative use between hospitals. Uniform registration and extraction procedures are necessary for appropriate measurement and interpretation and benchmarking of quantitative antibiotic use.