title: An additional measure for quantifying antibiotic use in hospitals.
abstract: OBJECTIVE
  The number of defined daily doses (DDD) per 100 patient days is often used as an indicator for the selection pressure exerted by antibiotics in the hospital setting. However, this unit of measurement does not fully describe the selection pressure and is sensitive to changes in hospital resource indicators. Additional information is required to facilitate interpretation of this indicator. The number of DDD per 100 admissions could be a valuable additional tool. The aim of this study is to investigate the importance of units of measurement in quantifying antibiotic use data with regards to antibiotic resistance risks.
  
  
  METHODS
  Trends in antibiotic use in acute care Dutch hospitals between 1997-2001 were studied. Antibiotic use was expressed in DDD per 100 patient days and in DDD per 100 admissions.
  
  
  RESULTS
  From 1997 to 2001, total systemic antibiotic use significantly increased from 47.2 to 54.7 DDD per 100 patient days, whereas expressed in DDD per 100 admissions it remained constant. Some individual antibiotics increases in DDD per 100 patient days were not accompanied by increases in DDD per 100 admissions and vice versa. The mean number of total DDD per hospital decreased (not significantly) between 1997 and 2001. The mean number of patient days, admissions and length of stay decreased significantly.
  
  
  CONCLUSIONS
  Knowledge of variation in resource indicators and additional expression of the data in DDD per 100 admissions is imperative for a meaningful understanding of observed trends in antibiotic use expressed in DDD per 100 patient days. Further research is needed to determine the correlation between different measures of antibiotic use and the level of antibiotic resistance.
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus MC, University Medical Center Rotterdam, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands. p.filius@erasmusmc.nl
authors.forename: P M G
authors.initials: PM
authors.lastname: Filius
authors.forename: T B Y
authors.initials: TB
authors.lastname: Liem
authors.forename: P D
authors.initials: PD
authors.lastname: van der Linden
authors.forename: R
authors.initials: R
authors.lastname: Janknegt
authors.forename: S
authors.initials: S
authors.lastname: Natsch
authors.forename: A G
authors.initials: AG
authors.lastname: Vulto
authors.forename: H A
authors.initials: HA
authors.lastname: Verbrugh
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D024881:Drug Resistance, Bacterial; D004363:Drug Utilization / Q000706:statistics & numerical data*; D006761:Hospitals; D006801:Humans; D009426:Netherlands; D010343:Patient Admission / Q000706:statistics & numerical data*; D010607:Pharmacy Service, Hospital / Q000706:statistics & numerical data
chemical_list: D000900:Anti-Bacterial Agents