Objective.To describe variability in rates of antibacterial use in a large sample of US hospitals and to create risk‐adjusted models for interhospital comparison.

Methods.We retrospectively surveyed the use of 87 antibacterial agents on the basis of electronic claims data from 130 medical‐surgical hospitals in the United States for the period August 2002 to July 2003; these records represented 1,798,084 adult inpatients. Hospitals were assigned randomly to the derivation data set (65 hospitals) or the validation data set (65 hospitals). Multivariable models predicting rates of antibacterial use were created using the derivation data set. These models were then used to predict rates of antibacterial use in the validation data set, which was compared with observed rates of antibacterial use. Rates of antibacterial use was measured in days of therapy per 1,000 patient‐days.

Results.Across the surveyed hospitals, a mean of 59.3% of patients received at least 1 dose of an antimicrobial agent during hospitalization (range for individual hospitals, 44.4%‐73.6%). The mean total rate of antibacterial use was 789.8 days of therapy per 1,000 patient‐days (range, 454.4‐1,153.4). The best model for the total rate of antibacterial use explained 31% of the variance in rates of antibacterial use and included the number of hospital beds, the number of days in the intensive care unit per 1,000 patient‐days, the number of surgeries per 1,000 discharges, and the number of cases of pneumonia, bacteremia, and urinary tract infection per 1,000 discharges. Five hospitals in the validation data set were identified as having outlier rates on the basis of observed antibacterial use greater than the upper bound of the 90% prediction interval for predicted antibacterial use in that hospital.

Conclusion.Most adult inpatients receive antimicrobial agents during their hospitalization, but there is substantial variability between hospitals in the volume of antibacterials used. Risk‐adjusted models can explain a significant proportion of this variation and allow for comparisons between hospitals for benchmarking purposes.