estimated 51.5 million errors during the filling of 3 billion prescriptions each year. One study of medication errors at Medco Health Solutions, Inc., a large mail order pharmacy, carried out by Medco employees, found a dispensing error rate of 0.075 percent—16 dispensing errors among 21,252 prescriptions (Teagarden et al., 2005).

Self-care studies have focused mainly on adherence rates, which are generally low. An early study found adherence rates for prescribed medications of 50 percent (Sackett and Snow, 1979). A more recent meta-analysis of 328 studies reporting on adherence to medication regimens found an adherence rate of 79.4 percent (DiMatteo, 2004). Adherence rates appear to vary according to the number of doses taken per day (Cramer et al., 1989).

Pediatric Care

It has become clear that the prescription, dispensing, and administration of medications account for a substantial portion of the preventable medical errors that occur with children (Kaushal et al., 2001, 2004). Children are uniquely vulnerable to medication errors: all pediatric medication doses need to be based on body-size parameters (e.g., weight, body mass index) and the state of organ development; children are much less able than adults to double-check their own medications; and the wide range of appropriate doses for any given medication based on the child’s size gives the “average” dose little predictability for those doing the administering. Accurate pediatric medication administration requires knowledge of the child’s precise weight; proper conversion of pounds to kilograms; the correct choice of appropriate preparations and concentrations; and the ability to measure and administer doses properly, particularly for liquid medications.

An inpatient study covering all types of medications carried out at two urban teaching hospitals reported a rate of medication order errors of 4.2 percent, or 405 prescribing errors per 1,000 pediatric patients (Kaushal et al., 2001). Using a broader definition of medication error, a French study reported a higher rate—24.0 percent (Fontan et al., 2003). Also using a broader definition, a still higher rate was observed in a pediatric ICU—30.0 percent (Potts et al., 2004).

Rates of administration errors were estimated to be 0.72 per 100 orders (or 7.0 per 100 admissions, or 19.8 per 1,000 patient days) for all types of medication in a pediatric inpatient setting (Kaushal et al., 2001) and 23.0 per 100 opportunities for error in a pediatric nephrology ward (Fontan et al., 2003).

There have been two pediatric emergency department studies. One of these, conducted in a Canadian hospital, estimated that 100.0 prescribing

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