700,000 adverse drug events in the U.S. each year lead to ER visits

Each year, an estimated 700,000 persons experience adverse drug events that lead to emergency department visits, according to a study in the October 18 issue of JAMA: The Journal of the American Medical Association.

Outpatient use of drug therapies in the United States is common. In 2004, 82 percent of the U.S. population reported using at least 1 prescription medication, over-the-counter medication, or dietary supplement in the previous week and 30 percent reported using 5 or more of these drugs, according to background information in the article. While these medications may offer substantial benefits, there also may be risks. Information on outpatient adverse drug events (ADEs) has been difficult to collect, but the problem is large and can be expected to increase.

Daniel S. Budnitz, M.D., M.P.H., of the Centers for Disease Control and Prevention, Atlanta, and colleagues analyzed data from the National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance project (NEISS-CADES) to determine the frequency and characteristics of ADEs in the U.S. that have led to emergency department visits. The study included data from Jan. 2004 through Dec. 2005.

Over the 2-year study period, 21,298 adverse drug event cases were reported. "Based on data from a nationally representative surveillance system, we estimate that more than 700,000 patients were treated for ADEs in U.S. emergency departments annually in 2004 and 2005, and 1 of every 6 required subsequent hospital admission, transfer to another health care facility, or emergency department observation admission. Individuals aged 65 years or older were more than twice as likely to be treated in emergency departments for an ADE and nearly 7 times as likely to require hospitalization as individuals younger than 65 years. Among all patients who were hospitalized, most ADEs were due to unintentional overdoses and two-thirds of these were due to toxicity from a relatively small set of drugs for which regular monitoring is commonly required to prevent acute toxicity. Sixteen of the 18 drugs most commonly causing ADEs have been in clinical use for more than 20 years," the authors write.

Adverse drug events accounted for 2.5 percent of estimated emergency department visits for all unintentional injuries and 6.7 percent of those leading to hospitalization, and also accounted for 0.6 percent of estimated emergency department visits for all causes.

Insulins or warfarin, drugs that typically require ongoing monitoring to prevent overdose or toxicity, were implicated in 1 in every 7 estimated ADEs treated in emergency departments.

"The finding that individuals aged 65 years or older (12 percent of the U.S. population) accounted for one-quarter of ADEs overall and half of adverse events requiring hospitalization highlights the importance of directing ADE prevention efforts to this vulnerable population. Emergency department visits for ADEs in this age group were nearly as common as those for motor vehicle occupant injuries," the authors write.

"Efforts to reduce the burden of outpatient ADEs have been hampered by sparse data, except in selected health care systems or settings. Ongoing data collection in NEISS-CADES will enable more detailed examination of the epidemiology of emergency department-treated outpatient ADEs, focusing on specific patient populations, drug classes, conditions, and circumstances. Identifying appropriate measures of drug exposure and evaluating drug risks in relation to drug benefits remain important challenges in improving the quality of outpatient drug therapy," the researchers write.


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