title: Validating hospital antibiotic purchasing data as a metric of inpatient antibiotic use.
abstract: OBJECTIVE
  Antibiotic purchasing data are a widely used, but unsubstantiated, measure of antibiotic consumption. To validate this source, we compared purchasing data from hospitals and external medical databases with patient-level dispensing data.
  
  
  METHODS
  Antibiotic purchasing and dispensing data from internal hospital records and purchasing data from IMS Health were obtained for two hospitals between May 2013 and April 2015. Internal purchasing data were validated against dispensing data, and IMS data were compared with both internal metrics. Scatterplots of individual antimicrobial data points were generated; Pearson's correlation and linear regression coefficients were computed. A secondary analysis re-examined these correlations over shorter calendar periods.
  
  
  RESULTS
  Internal purchasing data were strongly correlated with dispensing data, with correlation coefficients of 0.90 (95% CI = 0.83-0.95) and 0.98 (95% CI = 0.95-0.99) at hospitals A and B, respectively. Although dispensing data were consistently lower than purchasing data, this was attributed to a single antibiotic at both hospitals. IMS data were favourably correlated with, but underestimated, internal purchasing and dispensing data. This difference was accounted for by eight antibiotics for which direct sales from some manufacturers were not included in the IMS database. The correlation between purchasing and dispensing data was consistent across periods as short as 3 months, but not at monthly intervals.
  
  
  CONCLUSIONS
  Both internal and external antibiotic purchasing data are strongly correlated with dispensing data. If outliers are accounted for appropriately, internal purchasing data could be used for cost-effective evaluation of antimicrobial stewardship programmes, and external data sets could be used for surveillance and research across geographical regions.
authors.affiliation: Sunnybrook Research Institute, Toronto, Ontario, Canada.
authors.forename: Charlie
authors.initials: C
authors.lastname: Tan
authors.affiliation: Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Ritchie
authors.affiliation: North Bay Regional Health Centre, North Bay, Ontario, Canada.
authors.forename: Jason
authors.initials: J
authors.lastname: Alldred
authors.affiliation: Sunnybrook Research Institute, Toronto, Ontario, Canada Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada University of Toronto, Toronto, Ontario, Canada Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada nick.daneman@sunnybrook.ca.
authors.forename: Nick
authors.initials: N
authors.lastname: Daneman
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D004363:Drug Utilization; D006761:Hospitals; D006801:Humans; D007297:Inpatients
chemical_list: D000900:Anti-Bacterial Agents