Adverse drug events among hospitalized Medicare patients: epidemiology and national estimates from a new approach to surveillance.

BACKGROUND

Although adverse drug events (ADEs) are a well-recognized problem among hospitalized patients, there is no system for monitoring them. Six high-alert medications and associated adverse events were selected for inclusion in the Medicare Patient Safety Monitoring System (MPSMS), a national surveillance system designed to identify and track over time inpatient adverse events within the hospitalized fee-for-service Medicare population.

METHODS

Explicit chart review algorithms were used to identify medication exposures and associated adverse events from the the 2004 MPSMS sample's medical records. The associations of ADEs with patient characteristics, length of stay, mortality, and 30-day readmission were assessed with bivariate analyses and hierarchical linear regression modeling (HGLM) approaches. National ADE rates and numbers of adverse events were estimated using weighted HGLM.

RESULTS

On the basis of 25,145 hospital visits in the 2004 MPSMS sample, an estimated 8.2% of patients exposed to warfarin experienced associated ADEs, as did 13.6% exposed to heparin, 10.7% exposed to insulin/hypoglycemic agents, and 0.5% exposed to digoxin. Some 0.6% of patients exposed to antibiotics experienced antibiotic-associated Clostridium difficile infection (CDI). Patients with ADEs had increased length of stay and in-hospital and 30-day mortality, except that patients with antibiotic-associated CDI did not have increased in-hospital mortality, and patients with ADEs associated with heparin did not have increased 30-day mortality. An estimated 888,000 ADEs occurred in hospitalized Medicare patients from these medications alone.

DISCUSSION

This new approach to detecting ADEs and estimating the national burden of ADEs from selected medications may be adapted for other types of ADEs in the Medicare population and may offer guidance to policymakers on appropriate areas of focus for patient safety.