More than 700,000 cases of adverse drug events are treated each year in emergency departments, according to estimates based on a nationally representative sampling of U.S. hospitals.
Of these, an estimated 117,000, or 1 in 6, are so severe that they require hospitalization, transfer to another health facility, or an ED admission for observation, according to the study, which was published in the Oct. 18 issue of the Journal of the American Medical Association.
People aged 65 years and older accounted for one-quarter of these adverse drug events and for more than half of those that required hospitalization, making the magnitude of the problem in this age group equivalent to that for injuries from motor vehicle accidents. People in this age group were more than twice as likely to need ED treatment and nearly seven times as likely to need hospitalization as younger people.
These findings, the first to be reported from the National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance project, establish that adverse drug events are an important cause of morbidity, said Dr. Daniel S. Budnitz of the Centers for Disease Control and Prevention, Atlanta, and his associates.
The NEISS-CADES project assessed all incident ED visits explicitly attributed to the use of a drug at 63 hospitals that comprised a probability sample representative of all U.S. hospitals. The drugs included prescription and over-the-counter medications, vaccines, dietary supplements, and herbal products, but not illegal substances.
The adverse events included allergic reactions, undesirable pharmacologic or idiosyncratic effects that occur at recommended doses, toxic effects that stem from unintentional excess dosing or impaired excretion, and secondary effects such as falling because of drug-induced dizziness, the investigators said (JAMA 2006;296:1858–66).
Among the study's other findings:
▸ Most adverse drug events were due to unintentional overdoses. These include warfarin, insulin, and digoxin, which alone accounted for one-third of adverse events in older patients. Other such drugs were antidiabetic agents, anticonvulsants, theophylline, and lithium.
▸ The five most common drug classes implicated in adverse events were insulins, opioid-containing analgesics, anticoagulants, agents containing amoxicillin, and antihistamines/cold remedies.
▸ The most common drug reactions prompting the ED visits were dermatologic conditions, gastrointestinal problems, and neurologic conditions. Altered mental status, respiratory dysfunction, syncope, and cardiovascular effects also were common.
▸ About one-third of the adverse events were allergic reactions.
▸ Sixteen of the 18 drugs that caused most adverse events have been in use for over 20 years.
These results likely represent an underestimate of the total burden of adverse drug events, since they didn't include events treated in other settings, the researchers noted.
They also don't include adverse events unrecognized by ED physicians, according to Dr. Budnitz and his associates.