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Frequency and preventability of adverse drug events in the outpatient setting
  1. Rachel L Wasserman1,2,
  2. Heba H Edrees1,
  3. Mary G Amato1,
  4. Diane L Seger3,
  5. Michelle L Frits1,
  6. Andrew Y Hwang1,2,
  7. Christine Iannaccone1,
  8. David W Bates1,3,4
  1. 1 Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, USA
  2. 2 Massachusetts College of Pharmacy and Health Sciences, Boston, Massachusetts, USA
  3. 3 Clinical and Quality Analysis, Mass General Brigham, Somerville, Massachusetts, USA
  4. 4 Harvard Medical School, Boston, MA, USA
  1. Correspondence to Dr Rachel L Wasserman, Brigham and Women's Hospital Department of Medicine, Boston, USA; rwasserman{at}


Background Limited data exist regarding adverse drug events (ADEs) in the outpatient setting. The objective of this study was to determine the incidence, severity, and preventability of ADEs in the outpatient setting and identify potential prevention strategies.

Methods We conducted an analysis of ADEs identified in a retrospective electronic health records review of outpatient encounters in 2018 at 13 outpatient sites in Massachusetts that included 13 416 outpatient encounters in 3323 patients. Triggers were identified in the medical record including medications, consultations, laboratory results, and others. If a trigger was detected, a further in-depth review was conducted by nurses and adjudicated by physicians to examine the relevant information in the medical record. Patients were included in the study if they were at least 18 years of age with at least one outpatient encounter with a physician, nurse practitioner or physician’s assistant in that calendar year. Patients were excluded from the study if the outpatient encounter occurred in outpatient surgery, psychiatry, rehabilitation, and paediatrics.

Results In all, 5% of patients experienced an ADE over the 1-year period. We identified 198 ADEs among 170 patients, who had a mean age of 60. Most patients experienced one ADE (87%), 10% experienced two ADEs and 3% experienced three or more ADEs. The most frequent drug classes resulting in ADEs were cardiovascular (25%), central nervous system (14%), and anti-infective agents (14%). Severity was ranked as significant in 85%, 14% were serious, 1% were life-threatening, and there were no fatal ADEs. Of the ADEs, 22% were classified as preventable and 78% were not preventable. We identified 246 potential prevention strategies, and 23% of ADEs had more than one prevention strategy possibility.

Conclusions Despite efforts to prioritise patient safety, medication-related harms are still frequent. These results underscore the need for further patient safety improvement in the outpatient setting.

  • Patient safety
  • Ambulatory care
  • Medication safety

Data availability statement

No data are available.

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Data availability statement

No data are available.

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  • Contributors All authors contributed to the study conception; design; and acquisition, analysis or interpretation of the data. MGA, HHE, CI and DWB were responsible for study conception or design. RLW, MGA, DLS, MLF, AYH and HHE did the data cleanup and analysis. RLW, MGA, DLS and AYH were responsible for the first draft of the manuscript with all authors reviewing the draft and providing critical feedback. All authors contributed to and approved the final manuscript. DWB was the guarantor.

  • Funding This study was funded by RMF/CRICO (No award/grant number).

  • Competing interests DWB reports grants and personal fees from EarlySense, personal fees from CDI Negev, equity from ValeraHealth, equity from Clew, equity from MDClone, personal fees and equity from AESOP, personal fees and equity from Feelbetter, equity from Guided Clinical Solutions and grants from IBM Watson Health, outside the submitted work. DWB has a patent pending (PHC-028564 US PCT), on intraoperative clinical decision support.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.