Based on data on patients who presented in 1994 at the emergency department of a 560-bed teaching hospital, the costs of treating those with a preventable ADE experienced previously were $308 for those who were not hospitalized and $2,752 for those who were (Dennehy et al., 1996). The study found that 4 percent of all emergency department visits (50 of 1,260) were due to prior ADEs; of these ADEs, 66 percent were judged preventable.

In one study of 253 patients presenting to an emergency department, 71 (28 percent) made their visit because of an ADE (Tafreshi et al., 1999). Of these 71 visits, 50 (70.4 percent) were judged to be due to a preventable ADE. The average cost to the institution was approximately $1,444 for each preventable medication-related visit.

Costs of Medication Errors in Nursing Homes

A study of medication problems in one nursing home provided information on the costs of ADEs in the nursing home setting (Cooper, 1987). That study reported two cases of antibiotic-related errors (omission and known drug allergy) that resulted in hospitalizations costing $3,923 and more than $5,000, respectively. It was further reported (GAO, 2000) that preventable errors in that nursing home cost up to $340,942 over a 2-year period.

Costs of Medication Errors in Ambulatory Care

Only one study was found that addressed the cost of ADEs in ambulatory care. In a study carried out from July 1999 to June 2000, the estimated increased costs (relative to costs incurred in a matched comparison group) associated with ADEs and preventable ADEs among older adults in the ambulatory care setting were $1,310 and $1,983, respectively. Inpatient stays accounted for 71 percent of the additional costs for ADEs and 62 percent of the additional cost for preventable ADEs. Based on the study’s cost estimates and rates of ADEs, the annual costs related to ADEs and preventable ADEs in 1,000 older adults would be $65,631 and $27,365, respectively (Field et al., 2005).

Overall Costs of Preventable Medication Errors

In summary, our understanding of the cost of medication errors is very incomplete. Most of what we know relates to additional health care costs associated with preventable ADEs, which represent the injuries caused by errors:

  • Hospitals—Classen and colleagues (1997) projected 380,000 preventable ADEs occurring annually and Bates and colleagues (1995b)

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