Summary

About 2.7 billion prescriptions were filled in the United States in 1998. Although prescription drugs have great clinical benefits, serious adverse drug events can lead to hospitalization, disability, and even death. Adverse drug events are caused by harmful drug reactions or by medication errors committed by health care professionals and patients. Two factors that can increase the risk of a patients' suffering from an adverse drug event are illness severity and intensity of treatment, including taking several drugs simultaneously. Although it is clear that a wide range of commonly used drugs cause adverse drug events with potentially serious consequences for patients, relatively little is known about their frequency. Data routinely collected on adverse drug events during clinical trials or after drugs are marketed are intended to identify the adverse drug events that are associated with particular drugs and do not focus on their frequency. Information on the overall incidence of adverse drug events from all drugs has been limited to a few research studies that typically examined the experience of patients in one of two specific institutions--generally hospitals or sometimes nursing homes--leaving the overall incidence of adverse drug events in outpatient care largely unexplored. Greater understanding of certain factors that affect the likelihood of adverse drug events has led researchers and patient safety advocates to suggest a range of measures to decrease their number and severity. These proposals range from better communication between doctors and patients about the risks and benefits of medications to accelerating research on the safety of marketed drugs. Suggestions for reducing medication errors include developing computerized prescribing and dispensing systems to detect possible errors, increasing the role of pharmacists as advisers to physicians and as monitors of drug therapy, and improving health care providers' pharmaceutical education. GAO summarized this report in testimony before Congress; see: Adverse Drug Events: Substantial Problem but Magnitude Uncertain, by Janet Heinrich, Associate Director for Health Financing and Public Health Issues, before the Senate Committee on Health, Education, Labor and Pensions. GAO/T-HEHS-00-53, Feb. 1 (18 pages).

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.