Incidence and preventability of adverse drug events among elderly patients in the ambulatory setting

To assess the incidence and preventability of adverse drug events in the ambulatory setting, we performed a study of persons aged 65 or older cared for by a multispecialty group practice over a one-year period. Potential drug-related incidents were detected through various approaches including review of hospital discharges, review of emergency room notes, reports of healthcare providers, computer-generated signals, and automated review of electronic clinic notes. Medical record reviews were performed by clinical pharmacists, with subsequent classification of incidents by physician reviewers. Over 31,757 person-years of observation, 1530 adverse drug events were identified for an event rate of 48.2 per 1000 person years. Errors resulting in preventable adverse drug events occurred most often at the stages of monitoring, prescribing, and patient adherence. Overall, 28% of adverse drug events were judged preventable. We conclude that adverse drug events are common and often preventable among elderly patients in the ambulatory setting.