Frequency, type and clinical importance of medication history errors at admission to hospital: a systematic review

Methods

A structured search strategy was developed using relevant articles on file. We searched MEDLINE for English-language articles published from 1966 through April 2005 using the following MeSH (medical subject heading) terms: “medication history taking,” “medication errors,” “physicians,” “pharmacists,” “prescription medications,” “pharmaceutical preparations,” “hospital medication systems,” “hospital pharmacy services” and “medical records.” The search strategy was deliberately broad to ensure inclusion of the maximum number of relevant articles (details of the search strategy appear in on online appendix, available at www.cmaj.ca/cgi/content/full/173/5/510/DC1). All bibliographies of papers identified in the search were screened for additional articles, and this was done subsequently for all papers retrieved. We searched the EMBASE and CINAHL databases using a similar search strategy.

Two of us (V.C.T. and R.M.) identified relevant articles for retrieval by screening the titles, abstracts and subject headings of the MEDLINE citations for the following inclusion criteria: primary research article; comparison of physician-acquired medication histories (chart notes, admission orders or medication administration record) with comprehensive medication histories; adult inpatient population; and sample size of at least 30 patients. Full-text versions of the identified papers were retrieved and screened again by the 2 independent readers for the inclusion criteria.

All included articles were independently reviewed by 3 of us (V.C.T., N.F. and E.E.E.) for methodological features and results. Any discrepancies were resolved through discussion.

The reviewed studies were analyzed on the basis of their explicit descriptions of prospective or retrospective design, use of consecutively enrolled patients and adequate blinding. Quality grades were assigned as follows: grade A studies had prospective enrolment of consecutive patients and a sample size of at least 100 patients; grade B studies had prospective enrolment of consecutive patients and a sample size of less than 100; grade C studies included all other designs.

We sought data on prescription medication histories obtained by physicians at the time of hospital admission. Such data could include physician admission notes, admission medication orders or medication administration records. We also recorded data on the main comparative measure, which was usually a comprehensive medication history completed by a pharmacist. The comparative measure could have included a patient interview, a review of the physician's admission notes or admission medication orders, a review of medication lists, and contact with community pharmacists and physicians. An error in a prescription medication history was defined as a discrepancy between the medication history obtained by the physician and the comprehensive medication history. We also recorded discrepancies for nonprescription medications, allergy history and prior adverse drug reactions, when reported. Discrepancies between physician-acquired medication histories and comprehensive medication histories are not necessarily errors. Some “discrepancies” may be intentional therapeutic adjustments of the patient's usual medications by the treating physician. Physicians may choose to discontinue a specific medication, or adjust its dose, without documenting a reason in the chart. Therefore, we sought evidence from the studies of discussions with ordering physicians to distinguish intentional from unintentional discrepancies.

Certain medication history errors have more potential for harm than others. A reduction in laxative dose may have less consequence than the abrupt discontinuation of a β-blocker, for example. Therefore, we sought data from each study regarding the clinical importance of the errors.

We calculated the proportion of patients with 1 or more prescription medication history errors and the mean number of medication discrepancies per patient from each study whenever possible. The study methods and results were heterogeneous, and therefore we made no attempt to combine results for a meta-analysis.

Results

The screening and selection process of relevant studies is summarized in Fig. 1. No additional relevant papers were found in the EMBASE and CINAHL searches.

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Fig. 1: Method of study selection. *An additional study not indexed in MEDLINE was identified through review of relevant subspecialty journals.

We included 22 studies in our review. These studies enrolled a total of 3755 patients (range 33–1053, median 104). The methodological features of the studies are summarized in Table 1 (a more detailed version of the table is available online at www.cmaj.ca/cgi/content/full/173/5/510/DC2). Five studies had a prospective design and enrolled consecutive patients.4^,5^,10^,19^,23 Seven studies were retrospective.6^,9^,11^,14^,17^,18^,24 A total of 8 studies enrolled consecutive patients.4^,5^,6^,7^,10^,19^,21^,23 Four of the studies had a blinded design: the pharmacist investigators obtained their comprehensive medication histories independent of the physicians' medication histories.4^,8^,9^,25 Ten of the studies were conducted on medical wards,5^,9^,11^,12^,15^,17^,19^,21^,23^,25 4 on mixed medical and surgical wards,8^,13^,16^,22 2 on surgical wards,4^,6 1 in the emergency department7 and 1 in a psychiatric hospital;14 4 studies did not explicitly state the hospital ward setting.10^,18^,20^,24 Twelve of the studies described explicit inclusion and exclusion criteria; the most common inclusion criteria were that the patient was taking at least 1 prescription medication and that he or she was able to provide a medication history.

Interpretation

We found that discrepancies between physician-acquired prescription medication histories and comprehensive medication histories at the time of hospital admission were common, occurring in up to 67% of cases. Published studies reported that 10%–61% of patients had at least 1 omission error in their prescription medications, that 13%–22% had at least 1 commission error and that 60%–67% had at least 1 omission or commission error. Five studies explicitly distinguished between unintentional discrepancies (errors) and intentional therapeutic changes through discussions with ordering physicians. These studies found that up to 54% of patients had at least 1 medication history error and that 19%–75% of the errors were unintentional. Limited data suggested that 11%–59% of the medication history errors were clinically important.

Our review reveals that prescription medication history errors at the time of hospital admission are disturbingly common and potentially harmful to patients. Our review also uncovered important considerations for future studies. First, actual medication exposure in the hospital is best reflected by admission medication orders or medication administration records, not by physician chart notes. Second, the main comparator should be a comprehensive medication history that includes an interview, inspection of medication vials or lists, or both, and contact with community pharmacies or family physicians. Comprehensive medication histories routinely obtain more information than physician-acquired histories and have been found to be highly accurate when used in patient simulations where the “actual” medication use is known.8^,17 Third, there must be a distinction between intentional and unintentional discrepancies through discussion with ordering physicians. Fourth, a broad spectrum of errors, including those of omission, commission and dose or frequency, should be evaluated. Finally, the actual or potential clinical importance of the errors should be assessed.

Our review has several additional limitations. First, publication bias may have suppressed studies that showed low error rates. Second, our classification system for methodologic quality was arbitrary. Third, the studies in our review had a wide range of methods and results that made meta-analysis impossible. Although it is clear that prescription medication history errors are common, a precise description of the problem remains elusive. Some studies systematically overestimated errors because of the failure to distinguish between intentional and unintentional discrepancies. Other studies underestimated errors by focusing only on omission errors. Many studies excluded patients who could not provide a medication history; the error rate would likely be higher among such patients.

The results of our review indicate a need for a systematic approach to ensure the acquisition of accurate medication histories at the time of hospital admission. Physicians may benefit from additional training in obtaining complete medication histories. Such training may improve accuracy and may also help physicians recognize when a medication history is likely to be incomplete. There are many barriers to obtaining accurate medication histories, including patient illness, patient knowledge, availability of medication vials for inspection and lack of access to community pharmacy records. In addition, comprehensive medication histories take 9–30 minutes to complete,4^,5^,16^,17^,18^,23^,25 a potentially overwhelming task for busy admitting physicians. Pharmacists could be routinely involved in ensuring accurate medication histories at the time of admission, with particular attention to high-risk groups (e.g., patients with cognitive impairment using multiple medications). Patients and family members could assume a proactive role by bringing necessary medication information to the hospital and drawing attention to any deviations from the prescribed regimen. Integrated community pharmacy databases accessible to hospital staff could also enhance the accuracy of medication histories.