Adverse drug events and near misses: who’s counting?

It is no secret that drugs can harm as well as benefit a patient (1–3). In the Harvard Medical Practice Study, an intensive review of over 30,000 hospitalizations in New York State in the mid 1980s, drugs were the leading cause of medical injury, accounting for about one fifth of morbidity and mortality (4). Two terms describing these harms are in common use: the older of the two, adverse drug reaction (ADR), is defined as “any response to a drug which is noxious, unintended, and which occurs at doses normally used in man for the prophylaxis, diagnosis, or therapy of disease” (5) and includes only the appropriate use of drugs. The second, adverse drug event (ADE), can be defined as injury resulting from the use of a drug and includes medical errors. These definitions serve many purposes, including as outcomes in studies of medications, indicators for surveillance of drug complications, and sentinels in quality assurance. The Joint Commission on Accreditation of Healthcare Organizations (6) requires that hospitals have written procedures for recording and reporting ADRs. The Food and Drug Administration maintains that a concurrent surveillance system, driven by spontaneous, voluntary reporting of events by physicians, nurses, and pharmacists, is the best method of documenting ADRs. However, reporting has always been problematic (7). Estimates of the incidence of adverse drug reactions in hospitals have ranged widely, depending on the definition of events and the rigor of pursuit. A study in Boston hospitals suggested an incidence of 6.5 ADEs per 100 hospital admissions, which can be extrapolated to 1,900 ADEs per hospital per year, 1% of which are fatal (8). Although the precise incidence rates are arguable, it is widely recognized that older patients are highly vulnerable to ADEs (9 –11). Contributors include greater physiologic susceptibility, less functional reserve, and problems with recall; those with chronic illness may be under the care of multiple physicians and have more than one pharmacy filling many prescriptions, increasing the likelihood of inappropriate prescribing and drug-to-drug interactions (12). These problems are magnified by the disruptions that accompany acute illness, hospitalization, and return to the community (13–15). This issue of the Journal contains two articles that shed light on the epidemiology of ADEs and point out problems in reporting. In the first, Chyka (16) demonstrates a marked disparity between two national estimates of the number of deaths from ADRs. Tabulations of death certificates suggested 206 deaths in 1995 resulting from ADRs, whereas data from the Food and Drug Administration’s postmarketing surveillance system (MEDWatch) suggested 6,894 such fatalities. Which of these figures is correct? Probably neither, because both estimates are susceptible to underreporting by health professionals, who contributed only one of eight cases to MEDWatch. The author notes important disincentives to submitting reports, including fear of litigation, inadequate time to report, and lack of knowledge about how to report; he identifies this as a major problem with the current spontaneous reporting system. Gurwitz et al (17) studied ADEs and near misses (medication errors that did not result in adverse outcomes) in residents of 18 nursing homes in Massachusetts. Although others have broached the subject (18,19), this is the first report to provide true incidence data in a nursing home population. The team applied their own rigorous and previously tested methods for detection, including a structured review process and reports from nursing staff. The most important findings were that ADEs were common, and half were preventable, including the majority of severe outcomes. Scaling up their results to all US nursing homes, they estimate that approximately 24 ADEs and 8 potential ADEs should be identifiable each year in an average facility. This includes approximately 1,500 fatal and 18,000 life-threatening ADEs per year, 80% of which could be prevented. Perhaps equally important for this population, nearly 25,000 ADEs are disabling, with over 5,000 resulting in permanent disability. The surprise was how few ADEs they actually found, amounting to less than one ADE per resident-year. Examination of the pattern of ADEs leads to the suspicion of undercounting, because the errors found most frequently tended to be those most convenient to measure. Most events occurred at the stages of drug ordering (wrong dose or established drug– drug interaction) or monitoring (failing to monitor drug levels, or to act on abnormal findings). Psychoactive medications and anticoagulants were most commonly implicated. Errors less likely to be documented in the medical record, such as errors in administration, omissions, or wrong choice of drug, were also found less frequently. It is also surprising that the study tallied fewer near Am J Med. 2000;109:166 –168. From the Departments of Health Policy and Management, and Epidemiology, School of Hygiene and Public Health, and the Department of Medicine, School of Medicine, The Johns Hopkins University, Baltimore, Maryland. Requests for reprints should be addressed to Albert W. Wu, MD, MPH, Health Services Research and Development Center, 624 North Broadway, Baltimore, Maryland 21205.