The number of serious adverse drug events reported to the US Food and Drug Administration more than doubled between 1998 and 2005, as did related deaths, according to a new report.

Pain killers and immune-modifying drugs were singled out as the worst culprits by Thomas Moore and colleagues of the Institute for Safe Medication Practices, Huntingdon Valley, Pennsylvania, who analysed all the information obtained by the FDA through its Adverse Event Reporting System during this period.

Their report, in the Archives of Internal Medicine, found that a total of 467,809 serious adverse events were recorded. The annual number of reports increased 2.6-fold between 1998 and 2005, from 34,966 to 89,842 and the number of fatal adverse reactions increased from 5,519 to 15,107 – a 2.7-fold increase.

The FDA defines a serious adverse drug event as one that results in death, a birth defect, disability, hospitalisation, or is life-threatening or requires intervention to prevent harm. Such reports come to the agency directly from health professionals, or from drug manufacturers who are required to forward them.

"The overall relative increase was four times faster than the growth in total US outpatient prescriptions, which grew in the same period from 2.7 billion to 3.8 billion," the authors write. A total of 1,489 drugs were associated with adverse events but a subset of 51 drugs that each had 500 or more reports in any year accounted for 203,957 or 43.6% of the total adverse event reports in the study.

However, "contrary to our expectations, drugs related to safety withdrawals were a modest share of all reported events and declined in importance over time," the authors write. In the subset of 51 drugs with 500 or more reports in a year, the percentage of reported events associated with drugs related to safety withdrawals declined from 26% in 1999 to less than 1% in 2005.

"Among the most frequently reported drugs associated with fatal events, we observed a disproportionate contribution of pain medications and drugs that modify the immune system," they added, noting that “these data show a marked increase in reported deaths and serious injuries associated with drug therapy over the study period".

The authors conclude: "The results highlight the importance of this public health problem and illustrate the need for improved systems to manage the risks of prescription drugs." By Michael Day