Adverse drug events are harmful consequences from the therapeutic use of drugs. They include adverse consequences from reactions to drugs, adverse interactions between drugs, and the harm that comes from medication errors. They can be fatal. However, fatal adverse drug events are relatively rare, and most spontaneous reporting schemes and post-marketing studies contain few such cases. There is considerable uncertainty about both the incidence of fatal reactions and their likely causes.
The Institute of Medicine in the United States, extrapolating from information obtained in two relatively restricted hospital surveys, has suggested that as many as 98 000 deaths a year in the United States may be due to "medical error'' (Kohn et al., 1999). Lazarou et al. (1998) examined the evidence from 16 studies published between 1964 and 1995, and concluded that adverse drug reactions (ADRs) alone accounted for over 100 000 deaths in the United States in one year. This would mean that doctors and their treatments caused about 4% of all deaths. The extrapolation was based on a total of 78 deaths, the majority observed in studies conducted prior to 1976. The US General Accounting Office (2000) subsequently reported that "the magnitude of health risk [from adverse drug events] is uncertain, because of limited incidence data''.
Medication errors, that is, errors in prescribing, drawing up, and administering drugs, are a particularly important group of adverse drug events, because they are potentially preventable. The precise definition has proved difficult, but we have previously suggested the following: "a medication error is a failure in the treatment process that leads to, or has the potential to lead to, harm to the patient'' (Ferner and Aronson, 1999). "Failure" in this context signifies that the process has fallen below some attainable standard.
The contribution of medication errors to the overall figure for deaths from "medical error'' is not clearly established, but surveys of hospital in-patients (Bates et al., 1995) and of nursing homes
(Barker et al, 1982) have shown that medication errors are extremely common. Anecdotal reports from several sources, including Coroners' Inquests (Whittington and Thompson, 1983; Ayers et al., 1987; Whittington, 1991), and the medical defence societies (Ferner, 1995) have alerted doctors to some of the dangers.
One source of information which is potentially useful for investigating the epidemiology of adverse drug events is the records kept by Coroners in England and Wales.
INFORMATION FROM CORONERS' INQUESTS
Coroners in England and Wales have to determine how a person dies, if death is from a violent, unnatural, or unknown cause. Deaths due to errors in prescribing, dispensing, or giving drugs, and those caused by ADRs, fall within these categories. Coroners have extensive powers of investigation.
There are some caveats. The facts are not always clear, and so some deaths may be regarded as natural which in fact are due to therapy. Even if the facts are clear, the decision to report a death to the Coroner is not always straightforward, so some deaths might be reported by one doctor but not another. The extent of under-reporting is unknown. Each Coroner's Court covers deaths occurring in a defined area, so that, broadly speaking, the size of the population served by the Court is known. Local circumstances, such as the presence of a regional referral centre for some condition that is often fatal (such as liver failure), can however inflate the apparent incidence of deaths due to that cause.
We have previously described the findings in cases of death due to ADRs or to medication errors in one Coroner's district, Birmingham and Solihull, between 1986 and 1991 (Ferner and Whittington, 1994). Here we extend those data to cover the period January 1986 to June 2000.
The population in 1991 was 1.21 million people, and the number of deaths was approximately 15 000 per year, of which about a third were reported to the Coroner. An index of cases has been kept on computer since 1995, and prior to that, a card index was kept. The database was searched for "therapeutic/accident'', "therapeutic/ misadventure'', "medical mishap'' and ''medical misadventure''.
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