Key Definitions

Error: The failure of a planned action to be completed as intended (error of execution) or the use of a wrong plan to achieve an aim (error of planning). An error may be an act of commission or an act of omission (IOM, 2004).

Medication error: Any error occurring in the medication-use process (Bates et al., 1995a). Examples include wrong dosage prescribed, wrong dosage administered for a prescribed medication, or failure to give (by the provider) or take (by the patient) a medication.

Adverse drug event: Any injury due to medication (Bates et al., 1995b). Examples include a wrong dosage leading to injury (e.g., rash, confusion, or loss of function) or an allergic reaction occurring in a patient not known to be allergic to a given medication.

hospitals, errors are common during all steps of the medication-use process—procuring the drug, prescribing, dispensing, administering, and monitoring the patient’s response. In hospitals, they occur most frequently at the prescribing and administration stages.

Published error rates depend on the intensity and specifics of the error detection methods used. In particular, some methods are better suited to certain stages of the medication-use process. Detection methods addressing all stages but not including direct observation of administration found a rate of 0.1 prescribing errors per patient per day in a study of hospital pediatric units (Kaushal et al., 2001) and a rate of 0.3 prescribing errors per patient per day in a study of hospital medical units (Bates et al., 1995a). A major study using direct observation of administration (Barker et al., 2002) carried out at 36 different health care facilities found an administration error rate of 11 percent, excluding doses administered outside the scheduled time (“wrong-time” errors). Since a hospital patient receives on average at least ten medication doses per day, this figure suggests that on average, a hospital patient is subject to one administration error per day. Further, since prescribing and administration errors account for about three-fourths of medication errors (Leape et al., 1995), the committee conservatively estimates that on average, a hospital patient is subject to at least one medication error per day. Substantial variations in error rates are found, however. For the 36 facilities in the study mentioned above, the administration error rate (excluding wrong-time errors) ranged from 0 to 26 percent, with a median value of 8.3 percent (Barker et al., 2002).

A preventable ADE is a serious type of medication error. ADEs, defined as any injury due to medication (Bates et al., 1995b), are common in

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