Adverse drug events (ADEs) are common in hospitalized patients, but few empirical data are available regarding the strength of patient risk factors for ADEs.
We performed a nested case-control study within a cohort that included 4108 admissions to a stratified random sample of 11 medical and surgical units in 2 tertiary care hospitals during a 6-month period. Analyses were conducted on 2 levels: (1) using a limited set of variables available for all patients using computerized data available from 1 hospital and (2) using a larger set of variables for the case patients and matched controls from both hospitals. Case patients were patients with an ADE, and the matched control for each case patient was the patient on the same unit as the case patient with the most similar preevent length of stay. Main outcome measures were presence of an ADE, preventable ADE, or severe ADE.
In the cohort analysis, electrolyte concentrates (odds ratio [OR], 1.7), diuretics (OR, 1.7), and medical admission (OR, 1.6) were independent correlates of ADEs. Independent correlates of preventable ADEs in the cohort analysis were low platelet count (OR, 4.5), antidepressants (OR, 3.3), antihypertensive agents (OR, 2.9), medical admission (OR, 2.2), and electrolyte concentrates (OR, 2.1). In the case-control analysis, exposure to psychoactive drugs (OR, 2.1) was an independent correlate of an ADE, and use of cardiovascular drugs (OR, 2.4) was independently correlated with severe ADEs. For preventable ADEs, no independent predictors were retained after multivariate analysis.
Adverse drug events occurred more frequently in sicker patients who stayed in the hospital longer. However, after controlling for level of care and preevent length of stay, few risk factors emerged. These results suggest that, rather than targeting ADE-prone individuals, prevention strategies should focus on improving medication systems.