A serious adverse drug event, defined by the FDA, means death, a birth defect, disability, hospitalization or a life-threatening event or required intervention to prevent harm. Such events are voluntarily reported to the FDA through its Adverse Event Reporting System known as MedWatch reports.

Thomas J. Moore of the Institute for Safe Medication Practices in Huntingdon Valley, Penn., and colleagues analyzed serious adverse drug events reported to the FDA through AERS from 1998 through 2005.

During the study period, a total of 467,809 serious adverse events were reported -- a 2.6-fold increase from 34,966 to 89,842. The number of fatal adverse drug events increased from 5,519 to 15,107 in the same time frame -- a 2.7-fold increase.

The overall relative increase was four times faster than the growth in total U.S. outpatient prescriptions, which grew in the same period from 2.7 billion to 3.8 billion, the study reported in the Archives of Internal Medicine.

The report also found that a total of 1,489 drugs were associated with adverse events, but a subset of 51 drugs each had 500 or more reports in any year, or 43.6 percent of the total adverse event reports in the study.