Our results suggest that implementation of a basic CPOE system in the ambulatory setting is associated with a significant reduction in medication errors. Consistent with our hypothesis, the types of errors most easily mitigated by a basic CPOE system were reduced. Elimination of illegibility is inherent in the e-prescribing process. Forcing routine functions minimizes the use of inappropriate abbreviations and missing information. Pull-down menus mitigate other “wrongs” (eg, wrong strength). Despite the fact that our CPOE system lacked CDS alerts, reductions in numbers of drug–disease and drug–drug interaction errors were significant, although these occurred infrequently at baseline. Types of errors we would have thought would have occurred frequently with handwritten prescribing (eg, drug–drug interactions) occurred in ≤2% of prescriptions. Perhaps, due to our thorough evaluation methods, our evaluators were able to discern clinically meaningful versus theoretically relevant contraindications, interactions, and allergies. That the CPOE system did not affect the number of inappropriate laboratory monitoring errors suggests that CDS alerts are necessary to further decrease some of the more complex types of errors.
Implementation of the CPOE system was associated with a reduction in the number of errors at each severity level. Importantly, use of the CPOE system was associated with fewer errors that reached the patient (level B). Our model reveals that patients ≥65 years experienced more errors, but these were not associated with e-prescribing.
We used a MEDLINE search from 1997 to December 2008 to identify studies similar to ours. Bates' group was one of the first to demonstrate a significant reduction in serious errors (categories C through I) associated with an inpatient CPOE system, from 10.7 to 4.86 events per 1000 patient days (55% reduction; p<0.01). They noted a reduction in potential ADEs (C and D) from 5.99 to 0.98 events (84% reduction; p=0.002), and in actual ADEs of 4.69 to 3.88 (17% reduction; p=0.37).14
In a follow-on study, they noted an 86% reduction in serious medication errors (p<0.001), using an advanced CPOE/CDS system.15
Our results demonstrate a similar overall reduction rate of 55%, although our reductions in potential (9.8%) and actual (0.1%) ADEs were lower. These comparisons are not exact, as Bates' group excluded errors in categories A and B, while we included these. Our 70% reduction in odds of an error is similar to that noted in Shamliyan's meta-analysis.9
Of the investigations that have taken place in the ambulatory setting,11
only one is comparable.21
Gandhi retrospectively compared 1879 prescriptions that were handwritten versus e-prescribed using a basic CPOE system, and noted a reduction in errors (11.0% to 4.3%; p=0.31) and potential ADEs (4.0% to 2.6%; p=0.16). Although their results were not significant, the investigators suggested that CDS alerts could have prevented 97% of errors and 95% of potential ADEs. Our corresponding reductions were significant for errors, 18.0% to 8.2% (levels B–F; p<0.001), and for potential ADEs, 17.8% to 8.1% (B–D; p<0.001). Our rates are higher, but reductions similar in magnitude.
Jha et al
found that 1.4% of hospital admissions were due to ADEs and that 28% of these were preventable.46
Our rate of preventable ADEs was also <1%. Steele et al
's pre-, postevaluation assessed the effect on ordering behavior of drug-laboratory CDS alerts in the ambulatory setting.23
Applying the Naranjo algorithm,45
these investigators noted a trend toward fewer “definite” or “probable” ADEs (4.3% vs 10.3%; p=0.23). Using the Naranjo algorithm we found only “possible” associations between admissions and preventable ADEs, and these were tenuous, at best.
Although evidence suggests that well-designed CPOE/CDS systems can reduce error rates and improve care, most errors do not cause harm. However, even infrequently occurring preventable ADEs are unacceptable. Further, the benefits of CPOE/CDS systems are not limited to clinical outcomes; there are also cost implications. The cost of a preventable ADE in older adults has been conservatively estimated at $1983; a national average cost of $887 million (both 2000 $).47
These costs include inpatient stays (62%), emergency department visits (6%), outpatient care and physician fees (28%), and prescribed medications (4%). There are also costs associated with medication errors: prescriptions written without an indication, diseases not being treated, lack of adherence, and staff time spent preventing errors from becoming ADEs. These have yet to be estimated.
Some have noted that improved practitioner performance was associated with automatic prompts18
and homegrown software7
; that RR reductions were larger when e-prescriptions were compared with those that were handwritten,11
and when the rate of errors with handwritten prescriptions was >12%.9
Others noted greater effects in studies that used a manual chart review to detect errors.11
Our system was homegrown, our baseline error rate of handwritten prescriptions was 18%, and our methods included chart review. Perhaps these factors contributed to the magnitude of our error reduction rate.
Our study describes the benefits of a homegrown CPOE system in a community setting in the Northwest. To our knowledge, this is one of the largest studies conducted to date that evaluates this impact. During the study time frame, no other medication safety initiatives were implemented at any site within the clinic. Our sample size gave us power to detect a reduction in errors, although not in preventable ADEs. We limited our postimplementation analysis to only e-prescriptions. Prescribers still had the option of handwriting prescriptions, although few did, as adoption was rapid, and we allowed a 6-month lag time to achieve stability before evaluating prescriptions written postimplementation. Approximately 10% of prescriptions were handwritten at this juncture; these were written by prescribers across clinic sites and specialties. We could not blind our prescription reviewers as they viewed the actual prescriptions, either handwritten or e-prescribed. To achieve study feasibility, we limited our evaluation to prescriptions filled at the three pharmacies owned by The Everett Clinic. These prescriptions may differ from those filled elsewhere. Our analysis methods included a weighting variable to address this limitation. Ours was not a randomized trial, as is evidenced by some of the differences in characteristics of patients, prescribers, and prescriptions illustrated in . To address this limitation we used analytic methods that accounted for clustering on prescriber, effect modification of therapeutic drug class or site, and observable confounding. Finally, our inpatient chart review methods enabled us to capture information about ADEs, although our methods were not ideal for finding definitive links between medications and subsequent hospital admissions.
Research that further illuminates the patient safety benefits of CPOE/CDS systems is ongoing. Evidence that establishes these benefits is substantial for homegrown systems in the inpatient setting, but is not as robust in the ambulatory setting. Our work contributes to this knowledge base in the latter setting.