complementary and alternative medications. Most of the cost studies that have been carried out relate to ADEs associated with hospital care. This group of studies has examined both the costs of ADEs experienced in hospitals and the costs of emergency room visits or hospital admissions that are attributable to an earlier ADE. A few studies have examined the costs of ADEs in nursing home and ambulatory care. Some studies have used cost models of the health care delivery system to estimate annual national costs attributable to drug-related morbidity and mortality in ambulatory care.

As noted, hospital-related studies fall into two categories—those addressing the costs of ADEs experienced while in the hospital, and those addressing the costs of emergency room visits and hospital admissions that can be attributable to earlier ADEs.

Only one study was found that estimated the extra hospital costs of a preventable ADE occurring in a hospital. This study, carried out in 1993 within the Adverse Drug Events Prevention Study, found that after adjusting⁷ for patient comorbidities and case mix, the additional length of stay associated with a preventable ADE was 4.6 days, with an increase in total cost of $5,857 (Bates et al., 1997). From these data, the authors estimated that in a 700-bed teaching hospital, preventable ADEs resulted in an additional cost of $2.8 million per year (Bates et al., 1997).

A few studies have estimated the hospital/emergency room costs and the proportion of hospital admissions and emergency room visits attributable to an earlier preventable ADE.

In a study at a tertiary hospital, a computer-based monitoring program was used to identify admissions that may have been associated with an ADE. Among 3,238 admissions, 1.4 percent were found to be due to an ADE (Jha et al., 2001). Of these ADEs, 28 percent were preventable. Estimated costs were $10,375 per preventable ADE; annual costs to the hospital were $1.2 million per year for all preventable ADEs.