In our study of potential adverse drug events related to the usual medication reconciliation process, we found a high prevalence of unintentional medication discrepancies with potential for patient harm: an average of 1.4 per patient. Most PADEs were due to errors taking a medication history rather than errors of reconciling the medication history with patient orders. The majority of PADEs occurred at discharge rather than admission, and most errors were ones of omission. Predictors of the number of PADEs per patient included low patient understanding of their preadmission medications, number of high-risk medications, number of differences between preadmission and discharge medication regimens, and medication histories taken by an intern.
Our findings are consistent with those of other studies despite different conceptualization, definitions, and methods. Most studies corroborate that at least half of all patients have at least one PADE during the reconciliation process.4,14–16
In a single community hospital in Ontario, Canada, the rate of unintentional medication discrepancies was lower, but almost all admission discrepancies were corrected by study pharmacists before discharge orders were written.17
Previous studies have also shown that omissions are the most common type of medication discrepancy, with up to 61% of hospitalized patients having at least one drug omitted from their regimen.2,4,15
Our finding that PADEs are more often caused by errors of medication history-taking than by errors of reconciliation is not surprising when considering the difficulty of taking an accurate medication history in today’s healthcare environment. Multiple outpatient providers may each prescribe a subset of a patient’s medications, and none may take responsibility for ensuring the accuracy of the regimen as a whole. Incomplete data sources and inadequate communication among providers and patients may exacerbate this problem. In addition, patients may not have adequate health literacy to fully understand their medication regimens.18
The effort required to obtain an accurate list may therefore be substantial, including communication with community pharmacists, outpatient physicians, family members and caregivers, and time spent reviewing pill bottles with patients. A recent meta-analysis estimated that 27%-54% of patients suffer at least one unintentional medication discrepancy due to medication history errors.2
Conversely, the process of reconciling preadmission medications with discharge
orders requires attention to detail but is a less complex activity than taking an accurate medication history. Errors of reconciling preadmission medications with admission
orders, which are usually written by the same physician who took the medication history and performed shortly thereafter, are less common. The Joint Commission places equal weight on medication history-taking and admission and discharge reconciliation in its National Patient Safety Goals, yet reconciling medications at admission was the source of only 10 out of 257 PADEs in our study.
That more PADEs occurred with discharge than admission orders makes sense in light of the differences between inpatient and outpatient environments. The hospitalization itself is often brief and highly monitored in contrast to the post-discharge setting. Therefore, the same error (e.g., mild warfarin overdose) may have little potential for patient harm when written at admission but much greater potential for harm when written at discharge. In fact, in 313 cases, the same unintentional medication discrepancy occurred at admission and discharge, and in 79 of these (25%), the error was adjudicated as not being a PADE at admission but was considered a PADE at discharge.
Our finding that patients older than 85 were at lower risk for PADEs was surprising.19,20
This effect persisted when adjusted for number and classes of medications, sources used to generate the preadmission medication list, and several PCP characteristics. Outpatient physicians may be more careful about maintaining accurate medication lists in very old patients. There also may be unmeasured differences in the degree of medical and social supports these patients receive. In contrast, relying on family members or caregivers as a source of medication information in this study was a risk factor for PADEs. This factor may correlate with low functional status and high medical complexity. Family members may also represent a source of accurate medication information utilized by study pharmacists but not by medical teams.
That interns’ taking the medication history was an independent risk factor for PADEs, compared to more senior physicians, suggests either that medication history-taking improves with experience or that interns spend less time taking medication histories, perhaps as a result of competing demands or interruptions. Lack of time, training, or prioritization of medication history-taking could all serve as potential targets for future interventions.
The list of “high-risk” medications most associated with PADEs (muscle relaxants, lipid-lowering, antidepressant, gout, and respiratory medications) was somewhat different from that found in general studies of ADEs21–23
and from a recent study of discrepancies after discharge, which found cardiovascular, gastrointestinal, and pulmonary medications to be most common.24
Our high-risk medication list was adjusted for frequency of prescription, which made it more predictive and may account for some of these differences.
Limitations and Strengths
This study has several limitations. The study was conducted on general medical services at academic medical centers, and the results may not be generalizable to other settings. Patients with very short lengths of stay may have been disproportionately discharged prior to enrollment, thus leading to selection of a patient population on more medications and an overestimation of the number of PADEs per patient. The study measured potential and not actual ADEs. Our adjudication process was sometimes hindered by the lack of documentation of reasons for medication discrepancies. However, one could argue that intentional but undocumented medication discrepancies represent “latent” medical errors that could lead to downstream patient harm as subsequent providers try to determine why certain medication changes occurred. Finally, our use of pharmacists to establish a “gold-standard” preadmission medication regimen could be questioned. However, studies have shown that pharmacists perform this process better than other medical personnel,25
and we demonstrated moderately high reliability when the process was conducted independently by two pharmacists.
Our study also has several strengths. To our knowledge, our study is the first to distinguish errors of history-taking from those of reconciling that history with orders, which is highly relevant to the Joint Commission medication reconciliation mandate. To our knowledge, it is also the first study to propose a scoring system to identify patients at high risk for PADEs. Other strengths include a rigorous adjudication process of all discrepancies and conduct of the study at two different academic medical centers.
Based on the results of this study, interventions to improve medication safety at transitions in care should focus first and foremost on gathering accurate preadmission medication information, and secondly on preventing reconciliation errors at discharge. Comparatively less effort can be spent preventing reconciliation errors at admission. If our risk score is prospectively validated in other populations, it could be useful to identify patients who may need more than the minimum medication reconciliation standard, for example, greater pharmacist involvement in taking medication histories and/or counseling patients at discharge. Studies of medication reconciliation interventions of various types and in different populations are needed to demonstrate benefits to patients during transitions in patient care.