Lasser KE et al. (2006) Adherence to black box warnings for prescription medications in outpatients. Arch Intern Med 166: 338–344

Adverse events caused by prescribing drugs in violation of a 'black box' warning are thankfully rare—occurring in <1% of those who receive a contraindicated drug, according to results of an observational study of records from 51 outpatient practices in the greater Boston area. Despite this encouraging finding, the number of patients at risk is large; and adverse drug events are thought to cause ∼100,000 deaths annually in the US alone.

Lasser et al. report that 10% of adult outpatients given prescription medication received a drug bearing a black box warning; warning violations occurred in 7% of cases (2,354 of 33,778 patients). Seven drugs accounted for almost three-quarters of violations. The authors reviewed a randomly selected sample of 575 medical records, and identified 92 cases in which the warning violation could have resulted in an adverse effect, and four cases in which an adverse event actually occurred. All four were deemed preventable.

Clinical practice guidelines often contain different information to black box warnings, say the authors, and the latter can be vague and difficult to interpret. Compliance could be improved by devising a searchable online database of consistent, clear and simple warnings. With the increasing use of electronic health records, say Lasser et al., the potential of online alerts to support prescribing decisions, especially for drugs with the most commonly violated warnings, or those with the greatest potential to cause harm, should be explored.