Adverse Drug Reactions in Hospital and Ambulatory Care Settings Identified Using a Large Administrative Database

Background: Previous studies are limited in sample size and number of sites for the detection and characterization of adverse drug reactions (ADRs) in ambulatory care and hospital settings.

Objective: To determine the prevalence and distribution of suspected ADRs according to demographic characteristics and drug classes for ambulatory care and hospitalized patients.

Methods: A cross-sectional evaluation of administrative data from 2002-2005, containing a maximum of 20 million Medicare and commercially insured patients in a year, was completed. Individuals with one or more claims suggesting an ADR were identified, using International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) criteria referred to as a "suspected ADR." Frequency of ICD-9-CM codes consistent with suspected ADRs for the 4 years was calculated for hospital and ambulatory care settings, based on age ranges, comorbidities, and drug classes.

Results: Between 2002 and 2005, the average annual prevalence of suspected ADRs was 0.5%, with a total of 249,633 suspected ADRs during the 4 years. The mean age of hospitalized patients experiencing a suspected ADR was 12 years older than that of ambulatory care patients and 20 years older than that of the general database population. Diseases of the circulatory and endocrine/nutritional/metabolic systems rank among the top 5 comorbid conditions in hospitalized patients who had a suspected ADR. Injury and poisoning was the primary comorbidity in ambulatory patients. High-risk medications frequently associated with suspected ADRs in both settings were antineoplastic and anticoagulant agents. Other drug classes commonly associated with suspected ADRs in hospitalized patients were antihypertensives and diuretics. For the ambulatory care setting, drug classes frequently associated with suspected ADRs were antirheumatic and antiarteriosclerotic agents.

Conclusions: ADR detection, using administrative data, revealed differences in age, comorbidities, and drug classifications between ambulatory care and hospital settings. The results can be used to develop focused prevention strategies and targeted surveillance for individuals most at risk for developing ADRs.