Adverse drug events believed to be among the leading causes of mortality in the United States

Less than 1 percent of outpatients who received medication in 2002 were prescribed a medication that violated a prescription drug's black box warning, according to a study in the Archives of Internal Medicine.

"Adverse drug events (ADEs) are believed to be among the leading causes of mortality in the United States, with an estimated 100,000 deaths per year," according to background information in the article. However, there is little U.S. data on the occurrence of potentially dangerous drug-drug, drug-laboratory, and drug-disease interactions in outpatients. Black box warnings are separate, highlighted messages on drug labels that were developed by the Food and Drug Administration to help physicians avoid serious ADEs.

Karen E. Lasser, M.D., M.P.H., of Cambridge Health Alliance and Harvard Medical School, Cambridge, Mass., and colleagues, examined data from 51 outpatient practices to see how often physicians prescribed drugs in violation of black box warnings. The researchers analyzed electronic health records of 324,548 outpatients who received at least one prescription between January 1 and December 31, 2002.

The researchers found that 0.7 percent (2,354) of those outpatients received a prescription in violation of a black box warning. Of these patients who received a prescription with a black box warning, most (90.6 percent) were at risk for a drug-disease interaction, followed by a drug-laboratory interaction (26.6 percent; patient did not receive adequate monitoring) and a drug-drug interaction (3.3 percent). Patients who were white, female and 75 years of age or older and who took more medications were significantly more likely to be prescribed medications in violation of black box warnings. The researchers then analyzed a sample of 575 of the 2,354 patient records with prescriptions in violation of black box warnings and found that less than 1 percent of those patients had a documented adverse drug reaction as a result.

The researchers commented that similar studies have shown that prescribers fail to follow black box warnings much more frequently than observed in this study.

"We believe these data have implications for the Food and Drug Administration," the researchers write. "The Food and Drug Administration should make these warnings more specific, so that they are readily understandable by providers, and so that such providers can easily take action to avoid violating the warnings."