In this study, we evaluated the rate and type of ADEs in community hospitals, and found that the rates were fairly similar among these hospitals, but higher than those reported for large academic hospitals by about a factor of two, with about one patient in seven suffering an ADE. In addition, a much higher proportion of the ADEs were preventable in this study compared to prior studies from academic sites, with over two thirds preventable in this study, compared to less than a third in earlier studies. In addition to the ADEs, there were nearly three times as many potential ADEs. Many of the preventable ADEs appeared to be potentially preventable using CPOE, with drug-laboratory and renal dose checking being the two most important strategies.
In contrasting these results to other prior work, one helpful comparator is the ADE Prevention Study, done at two tertiary referral university hospitals in the same geographical area, which found a rate of 6.5 ADEs and 5.5 potential ADEs/100 patient admissions3
. Comparisons between the results must be made with circumspection for several reasons; the studies were conducted a number of years apart, somewhat different detection approaches were used in the two studies, and the patients in the earlier study were much younger—nearly 10 years younger on average, with a mean age of 52.5 years. In particular, the triggers sought in this study were more specific, although many of the same triggers were used in the earlier work. The earlier approach also included stimulated reporting (nurse investigators solicited information from nurses, pharmacists, and clerical staff at least twice daily to report incidents) as well as spontaneous reporting, although these two categories contributed very small numbers of events relative to chart review. In the present study, there was no interaction with the clinical staff prescribing the drugs. This should have biased the results toward finding more ADEs in the ADE Prevention Study, though we found the opposite. The differences in rates could also relate to differences in presence of house staff, work flow, and education of staff, or case mix. Furthermore, the ADE rates among the six community hospitals themselves also varied to some degree, although all had higher ADE rates than in the earlier study. In a particularly relevant study, Kilbridge et al. compared the automatically detected ADE rates between a university hospital and a community hospital using a detection rules engine14
. They found a 1.4 times higher ADE rate of 6.2/100 admissions at the community hospital (4.4/100 admissions at the university hospital). They also found that the type of ADE encountered differed in the two hospitals: the rates of antibiotic-associated diarrhea, drug-induced hypoglycemia, and anticoagulation-related ADEs were significantly higher at the community hospital.
In this study, about seven in ten ADEs were judged preventable and up to 97.5% of potential ADEs were not intercepted, leaving room for improvement. CPOE systems have been found to be efficacious in reducing the serious medication error rate by half, and early versions reduced the preventable ADE rate by almost one fifth2,4
. Better performance might be expected with additional decision support15,16
. In a systematic review that evaluated the effect of CPOE with CDS on reducing ADEs, five out of ten studies showed a significant reduction of ADEs17
The drug classes we found to be most often involved in preventable ADEs were cardiovascular drugs, analgesics, and antibiotics. Bates et al. found in the 1995 study that the drug classes responsible for preventable ADEs were 29% analgesics, 10% sedatives, and 9% antibiotics3
. Regarding non-preventable ADEs, analgesics and antibiotics led the list with 30% each in that study. Thus, in this study, cardiovascular drugs appeared more prominent as a cause of preventable ADEs than in the prior work; this may well reflect to some extent the common use of these drugs in the elderly.
In the ADE Prevention Study, wrong dose errors were most frequent, followed by wrong choice, known allergy, wrong frequency, and drug-drug interaction18
. In contrast, in this study, drug-laboratory issues were most frequent regarding ADEs, and dosing issues, allergy issues, and drug-drug interactions were much less important. It is unclear why these profiles are so different, though it is possible that more drug-allergy and drug-drug interaction issues are being detected in the pharmacy than at that time. However, for strategies for potential ADEs, drug dose interventions were the most important, followed by renal function checking. The potential of strategies using CPOE and the laboratory has been discussed previously, especially with respect to the importance of linking laboratory to drug data19
. Our study shows that checks involving laboratory data (laboratory-drug and renal checks taken together) could reduce preventable ADEs by 46.7%. Hulse et al. found a very similar rate of 44.9% drug-laboratory issues in patients with potential drug problems20
. Schiff et al. have described ten ways how laboratory parameters can help prevent medication errors such as suggesting contraindication of specific drugs, alteration of dosage and titration, as well as signaling signs of toxicity19
Kappa statistics for inter-rater reliability using this methodology in prior studies have been shown to range from 0.81 to 0.98 for the presence of an ADE and 0.92 for preventability; kappa was lower for decisions regarding severity (κ
0.32 to 0.37)3
. Inter-rater reliability in this study was similar to those earlier studies. In general, the range of kappa may vary substantially in rating incidents from 0.32-0.988
The incidence of serious medication errors can be significantly reduced using CPOE systems, but implementing these systems is very costly. Because CPOE is so expensive, the return on investment for implementing it is of great public and policy interest. A recent study done by Kaushal et al. showed that in the case of a 720-bed tertiary referral teaching hospital over 10 years cumulative net savings of $28.5 million are met by a $16.7 million net operating budget resulting in savings of $9.5 million, although it is unclear how these results would translate to the community setting21
. Another point is the reduction of LOS by preventing ADEs. In our study, patients with ADEs stayed 0.77 days longer in the hospital compared to patients without ADEs. This is only about half of what others have observed: Classen et al. found an excess length of hospital stay attributable to ADEs of 1.74 days, and Bates et al. found an increase of 2.2 days22,23
. The difference may be partly explained by the study design (both of these studies used case controls); hence, the estimate of increase of LOS in this study may be conservative.
Our study has several limitations. This study was carried out in just six hospitals in one region, and they may not be representative of other community hospitals in other regions. Although random sampling with trigger tools is a widely acknowledged methodology for measuring ADE incidence in hospitals24
, it almost certainly does not identify all ADEs occurring at a test site, and the ADEs found are probably not a random sample of all ADEs. However, we felt it was the most efficient way of detecting ADEs in the short term in institutions without CPOE or an EMR in place. We did not assess the reliability of nursing detection of signals in this evaluation, and some ADEs were undoubtedly missed. In some of the study sites CPOE systems were about to be implemented, which might have caused a higher awareness of the medical staff regarding drug safety issues as compared with to other sites. The study was intended to assess the incidence of ADEs in a group of community hospitals, and we did not intend to compare the hospitals with each other and had limited power to detect differences in rates between the hospitals.
In summary, we found that the incidence of ADEs in community hospitals was high, higher than rates in large academic hospitals measured previously, and a larger fraction of ADEs were preventable, although these comparisons must be made with circumspection given the differences between the cohorts. These data suggest that implementation of CPOE systems in community hospitals is likely to be beneficial if the benefits achieved in this setting are similar to those found in academic settings, which remains to be determined.