Adverse Drug Events:

The Magnitude of Health Risk Is Uncertain Because of Limited Incidence Data

HEHS-00-21: Published: Jan 18, 2000. Publicly Released: Feb 1, 2000.

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William J. Scanlon
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Pursuant to a congressional request, GAO summarized from available research what is known about adverse drug events (ADE), focusing on the: (1) different types and causes of ADEs; (2) evidence on the overall incidence and cost of ADEs in the United States; and (3) measures that have been proposed to reduce the number and severity of ADEs.

GAO noted that: (1) ADEs arise either from adverse drug reactions (ADR), which are previously known or newly detected side effects of drugs, or from medication errors committed by health care professionals or the patients themselves; (2) two factors that can increase the risk of a patient's suffering from an ADR are illness severity and intensity of treatment, including taking several drugs simultaneously; (3) studies of several hospital populations found that most medication errors did not cause ADEs, but because so many drug doses were given, an estimated quarter to half of all ADEs among the hospital patients resulted from medication errors; (4) other studies found medication errors were most often the result of physicians' prescribing errors and nurses' errors in administering drugs; (5) certain classes of drugs have consistently been associated with medication errors, including analgesics, antibiotics, psychotropics, and cardiovascular drugs; (6) although it is clear a wide range of commonly used drugs cause ADEs, little is known about their frequency; (7) data routinely collected on ADEs during clinical trials or after drugs are marketed are intended to identify the ADEs that are associated with particular drugs and do not focus on their frequency; (8) information on the overall incidence of ADEs from all drugs is limited to a few research studies that typically examined the experience of patients in one or two specific institutions leaving the overall incidence of ADEs in outpatient care largely unexplored; (9) the most broadly based information on ADE incidence comes from two studies drawing on statewide samples of hospital patients; (10) these studies applied a particularly restrictive definition of ADE in finding that ADEs occurred at a rate of 0.56 for every 100 patients in Colorado and Utah, 0.72 in New York; (11) although studies have estimated the overall rate of fatalities from ADEs and the total costs of treating ADEs, their estimates are open to question because of the limited underlying data on overall incidence available to support them; (12) greater understanding of certain factors that affect the likelihood of ADEs has led researchers and patient safety advocates to suggest a range of measures to decrease their number and severity; and (13) proposals for reducing ADRs include improving communication between patients and physicians about the risks and benefits of medications, and expanding and accelerating research on the safety of marketed drugs to more quickly detect previously unknown ADRs and determine the risk factors that increase their likelihood.

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