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Trends in outpatient antibiotic use and prescribing practice among US older adults, 2011-15: observational study

BMJ 2018; 362 doi: (Published 27 July 2018) Cite this as: BMJ 2018;362:k3155
  1. Scott W Olesen, postdoctoral fellow1,
  2. Michael L Barnett, assistant professor2 3,
  3. Derek R MacFadden, research fellow4 5,
  4. Marc Lipsitch, professor1 5,
  5. Yonatan H Grad, assistant professor1 6
  1. 1Department of Immunology and Infectious Diseases, Harvard T H Chan School of Public Health, Boston, MA, USA
  2. 2Department of Health Policy and Management, Harvard T H Chan School of Public Health, Boston, MA, USA
  3. 3Division of General Internal Medicine and Primary Care, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
  4. 4Division of Infectious Diseases, Department of Medicine, University of Toronto, Toronto, ON, Canada
  5. 5Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T H Chan School of Public Health, Boston, MA, USA
  6. 6Division of Infectious Diseases, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
  1. Correspondence to: Y H Grad ygrad{at} (or @yhgrad on Twitter)
  • Accepted 4 July 2018


Objective To identify temporal trends in outpatient antibiotic use and antibiotic prescribing practice among older adults in a high income country.

Design Observational study using United States Medicare administrative claims in 2011-15.

Setting Medicare, a US national healthcare program for which 98% of older adults are eligible.

Participants 4.5 million fee-for-service Medicare beneficiaries aged 65 years old and older.

Main outcome measurements Overall rates of antibiotic prescription claims, rates of potentially appropriate and inappropriate prescribing, rates for each of the most frequently prescribed antibiotics, and rates of antibiotic claims associated with specific diagnoses. Trends in antibiotic use were estimated by multivariable regression adjusting for beneficiaries’ demographic and clinical covariates.

Results The number of antibiotic claims fell from 1364.7 to 1309.3 claims per 1000 beneficiaries per year in 2011-14 (adjusted reduction of 2.1% (95% confidence interval 2.0% to 2.2%)), but then rose to 1364.3 claims per 1000 beneficiaries per year in 2015 (adjusted reduction of 0.20% over 2011-15 (0.09% to 0.30%)). Potentially inappropriate antibiotic claims fell from 552.7 to 522.1 per 1000 beneficiaries over 2011-14, an adjusted reduction of 3.9% (3.7% to 4.1%). Individual antibiotics had heterogeneous changes in use. For example, azithromycin claims per beneficiary decreased by 18.5% (18.2% to 18.8%) while levofloxacin claims increased by 27.7% (27.2% to 28.3%). Azithromycin use associated with each of the potentially appropriate and inappropriate respiratory diagnoses decreased, while levofloxacin use associated with each of those diagnoses increased.

Conclusion Among US Medicare beneficiaries, overall antibiotic use and potentially inappropriate use in 2011-15 remained steady or fell modestly, but individual drugs had divergent changes in use. Trends in drug use across indications were stronger than trends in use for individual indications, suggesting that guidelines and concerns about antibiotic resistance were not major drivers of change in antibiotic use.


  • Contributors: SWO, MLB, and YHG conceived of and designed the work. SWO analyzed the data. SWO and YHG drafted the work. All authors revised the work critically and approved the final manuscript. YHG is the guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

  • Funding: SWO and ML were supported by cooperative agreement U54GM088558 from the US National Institute of General Medical Sciences. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of General Medical Sciences or the National Institutes of Health. This funding source had no role in the design of this study and will not have any role during its execution, analyses, interpretation of the data, or decision to submit results.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: support from the US National Institute of General Medical Sciences for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: This study was deemed exempt from review by the institutional review board at the Harvard T H Chan School of Public Health, Boston, MA, USA.

  • Data sharing: All data are available from the Centers for Medicare and Medicaid Services.

  • The lead author (the manuscript’s guarantor) affirms that the manuscript is an honest, accurate, and transparent account of the study reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

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