Patterns of Antibacterial Use and Impact of Age, Race/Ethnicity, and Geographic Region on Antibacterial Use in an Outpatient Medicaid Cohort

STUDY OBJECTIVES To describe patterns of outpatient antibacterial use among California Medicaid (Medi-Cal) fee-for-service system beneficiaries, and to investigate the influence of demographic factors-age, race/ethnicity, state county, and population density-on those patterns. DESIGN Retrospective analysis of administrative claims data. DATA SOURCE Medi-Cal fee-for-service system claims database. PATIENTS All outpatient Medi-Cal fee-for-service system beneficiaries enrolled between 2006 and 2011 who had at least one systemic antibacterial claim. MEASUREMENTS AND MAIN RESULTS Rates of antibacterial prescribing and the proportion of broad-spectrum antibacterial use were measured over the study period and among age, racial/ethnic, and geographic (county) groups. Of the 10,018,066 systemic antibacterial claims selected for analysis, antibacterial prescribing rates decreased from 542 claims/1000 beneficiaries in 2006 to 461 claims/1000 beneficiaries in 2011 (r = -0.971, p=0.0012; tau-b = -1.00, p=0.009). Among age groups, children had the highest rate of use (605 claims/1000 beneficiaries, chi(2) (2) = 320,000, p<0.001); among racial/ethnic groups, Alaskan Natives and Native Americans had the highest rate of use (1086/1000 beneficiaries, chi(2) (5) = 197,000, p<0.001). Broad-spectrum antibacterial prescribing increased from 28.1% (95% confidence interval [CI] 28.1-28.2%) to 32.7% (95% CI 32.6-32.8%) over the study period. Senior age groups and whites received the highest proportions of broad-spectrum agents (53.4% [95% CI 52.5-54.3%] and 36.6% [95% CI 36.6-36.7%], respectively). Population density was inversely related to both overall antibacterial use (rho = -0.432, p=0.0018) and broad-spectrum antibacterial prescribing (rho = -0.359, p<0.001). The rate of prescribing decreased over the study period for all antibacterial classes with the exception of macrolides and sulfonamides. Amoxicillin was the most frequently prescribed agent. CONCLUSION Overall and broad-spectrum antibacterial use in the Medi-Cal fee-for-service program are less than that observed nationally. Significant variations in prescribing exist between age and racial/ethnic groups, and heavily populated areas are associated with both less antibacterial use and less broad-spectrum antibacterial prescribing. Studies are needed to determine the reasons for the observed differences in antibacterial use among demographic groups.