Ambulatory Computerized Prescribing and Preventable Adverse Drug Events

Background: Adverse drug events (ADEs) represent a significant cause of injury in the ambulatory care setting. Computerized physician order entry reduces rates of serious medication errors that can lead to ADEs in the inpatient setting, but few studies have evaluated whether computerized prescribing in the ambulatory setting reduces preventable ADE rates in ambulatory care. Objective: To determine the rates of preventable ADEs before and after the implementation of computerized prescribing with basic clinical decision support for ordering medications. Design: Before-after study of ADE rates in practices implementing computer order entry. Participants: Adult patients seeking care in primary care practices at academic medical centers in Boston, Massachusetts (n = 41,819), and Indianapolis, Indiana (n = 9128). Main Measures: We attempted to standardize the medication-related decision support knowledge base provided at the 2 sites, although the electronic records and presentation layers used at the 2 sites differed. The primary outcome was preventable ADEs identified based on structured results or symptoms defined by extracting symptom concepts from provider notes; potential ADEs were a secondary outcome. Results: Computerized prescribing did not significantly change the rate of preventable ADEs at either site. Compared with Boston practices, the rate of potential ADEs was more than seven-fold greater at Indianapolis (6.4/10,000 patient-months vs. 49.5/10,000 patient-months, P < 0.001). Computerized prescribing was associated with a 56% decrease in the potential ADE rate at Indianapolis (49.5 to 21.9/10,000 patient-months, P < 0.001) but a 104% increase at Boston (6.4 to 13.0/10,000 patient-months, P < 0.001). Preventable ADEs that occurred after computerized prescribing was implemented were due to patient education issues, physicians ignoring feedback from CDSS, and incomplete computerized knowledge base was incomplete (34%, 33%, and 33% in Indianapolis and 44%, 28%, and 28% in Boston). Conclusions: The implementation of computerized prescribing in the ambulatory setting was not associated with any change in preventable ADEs but was associated with a decrease in potential ADEs at Indianapolis but an increase at Boston, although the absolute rate of ADEs was much lower in Boston.