Geographic variation in outpatient antibiotic prescribing among older adults.

BACKGROUND Consequences of antibiotic overuse are substantial, especially among older adults, who are more susceptible to adverse reactions. Findings about variation in antibiotic prescribing can target policy efforts to focused areas; however, little is known about these patterns among older adults. METHODS Using Medicare Part D data from January 1, 2007, through December 31, 2009 (comprising 1.0-1.1 million patients per year), we examined geographic variation in antibiotic use among older adults in 306 Dartmouth Atlas of Health Care hospital referral regions, 50 states and the District of Columbia, and 4 national regions (South, West, Midwest, and Northeast). In addition, we examined the quarterly change in antibiotic use across the 4 regions. Differences in patient demographics, insurance status, and clinical characteristics were adjusted for across regions. RESULTS Substantial geographic and quarterly variation in outpatient antibiotic prescribing existed across regions after adjusting for population characteristics. This variation could not be explained by differences in the prevalences of the underlying conditions. For example, the ratios of the 75th percentile to the 25th percentile of adjusted annual antibiotic spending were 1.31 across states and 1.32 across regions. The highest antibiotic use was in the South, where 21.4% of patients per quarter used an antibiotic, whereas the lowest antibiotic use was in the West, where 17.4% of patients per quarter used an antibiotic (P < .01). Regardless of region, the rate of antibiotic use was highest in the first quarter (20.9% in January through March) and was lowest in the third quarter (16.9% in July through September) (P < .01). CONCLUSIONS Areas with high rates of antibiotic use may benefit from targeted programs to reduce unnecessary prescription. Quality improvement programs can set attainable targets using the low-prescribing areas as a reference, particularly targeting older adults.