Study: Adverse drug events cause ED visits

Some 700,000 U.S. residents go to hospital emergency departments (EDs) each year because of adverse drug events (ADE), according to research reported in the Oct. 18 issue of the Journal of the American Medical Association. One-sixth of those ED visits led to hospitalization of the patient in an inpatient care unit or ED observation bed.

The researchers said people ages 65 and older are more than twice as likely to be treated in an ED for an ADE than younger people, and are nearly seven times as likely to require hospitalization. ED visits for ADEs in the 65+ age group "were nearly as common as those for motor vehicle occupant injuries," the report said. They said their findings highlight the importance of directing ADE prevention efforts to that vulnerable population.

To reach their conclusions, researchers analyzed data from the federal government's National Electronic Injury Surveillance System, which tracks information from a nationally representative sample of 63 hospitals. The study included data from January 2004 through December 2005. In this period, 21,298 ADE cases were reported. Based on those reports, the researchers estimated that 701,547 patients visited an ED each year as a result of an ADE.

Most of the hospitalizations from an ADE were attributed to unintentional overdoses of medication, the researchers said. Drugs that commonly require outpatient monitoring to prevent acute toxicity, such as antidiabetic agents, warfarin, anticonvulsants, digitalis glycosides, theophylline, and lithium, were involved in most of the unintentional overdoses, the authors said. Those drugs were implicated in 66% of estimated overdoses requiring hospitalization and 41.5% of all estimated hospitalizations, they said. However, among patients ages 65 and older, those drugs were implicated in 85.4% of estimated overdose ED visits, 87% of estimated overdoses requiring hospitalization, and 54.4% of all estimated hospitalizations for that age group.

Five common drug classes

Overall, the five most common drug classes implicated in ADE-connected hospitalizations were anticoagulants, insulins, opioid-containing analgesics, oral hypoglycemic agents, and antineoplastic agents, the researchers said.

Of the 18 medications most commonly involved in an ADE that led to an emergency room visit, 16 have been in clinical use for more than 20 years, they said.

More than 80% of the U.S. population in 2004 reported using at least one prescription medication, nonprescription drug, or dietary supplement, and 30% reported using five or more products. An aging population, a trend toward outpatient delivery service, development of new prescription medications, the transition of many prescription medications to nonprescription status, and the increasing use of drugs for chemoprevention will likely increase outpatient drug use, the authors said.

They said while much attention and effort have been directed to measuring, understanding, and preventing ADEs in hospitalized patients, "less attention has been focused on ADEs occurring outside of health care facilities. Efforts to reduce the burden of outpatient ADEs have been hampered by sparse data, except in selected health care systems or settings," the researchers concluded.