hospitals, nursing homes, and the outpatient setting. ADEs associated with a medication error are considered preventable. The committee estimates that at least 1.5 million preventable ADEs occur each year in the United States:
Hospital care—Classen and colleagues (1997) projected 380,000 preventable ADEs occurring annually, and Bates and colleagues (1995b) 450,000. These are likely underestimates given the higher preventable ADE rate of another study using more comprehensive ADE identification methods (Jha et al., 1998).
Long-term care—Gurwitz and colleagues (2005) projected 800,000 preventable ADEs, again likely an underestimate given the higher ADE rates of other studies.
Ambulatory care—Among outpatient Medicare patients alone, Gurwitz and colleagues (2003) projected 530,000 preventable ADEs. Their approach was conservative, however, because it did not involve direct contact with patients, which yields much higher rates (Gandhi et al., 2003).
The above data exclude errors of omission—failure to prescribe medications for which there is an evidence base for the ability to reduce morbidity and mortality. With respect to such errors, the committee found well-documented evidence of inadequate treatments for acute coronary syndromes, heart failure, chronic coronary disease, and atrial fibrillation, as well as inadequate antibiotic and thrombosis prophylaxis in hospitals.
Current understanding of the costs of medication errors is highly incomplete. Most of what is known relates to additional health care costs associated with preventable ADEs, which represent the injuries caused by errors.
For hospital care, there is one estimate of the extra costs of inpatient care for a preventable ADE incurred while in the hospital—$5,857 (Bates et al., 1997). This figure excludes health care costs outside the hospital and was derived from 1993 cost data. Assuming conservatively an annual incidence of 400,000 in-hospital preventable ADEs, each incurring extra hospital costs of $5,857, yields an annual cost of $2.3 billion in 1993 dollars or $3.5 billion in 2006 dollars.
For long-term care, as noted earlier, Gurwitz and colleagues (2005) projected an annual incidence of 800,000 preventable ADEs. However, there is no estimate of the associated health care costs for this group of preventable ADEs.
For ambulatory care, the best estimate derives from a study (Field et al., 2005) that calculateed the annual cost of preventable ADEs for all Medi-