This study was conducted at Northwestern Memorial Hospital in Chicago, Illinois, and approved by the Institutional Review Board of Northwestern University. The study was designed to obtain in-depth, pharmacist interviews within 24–48 h of hospital admission with at least 400 adult medicine service patients. Our sample size was derived from preliminary power calculations indicating that a two-group chi-square test with p
0.05 two-sided significance level will have 88% power to detect the difference between a group of patients with a risk factor proportion of 0.20 and another group of patients with a risk factor proportion of 0.35 (odds ratio of 2.15) when the sample sizes are 134 and 267, respectively (a total sample size of 400).
Over 14 months in 2006–2007, study pharmacists obtained a list of patients admitted the previous day. Patients with limited English proficiency (LEP), reporting their understanding of English as “fair,” “poor” or “not at all” during hospital registration (less than 5% of medicine service admissions), were prioritized and interviewed using a language line phone service. All other eligible, sampled inpatients were approached sequentially, based on daily generated random numbers, by one of two study pharmacists during their available (Monday through Friday) research time. Any patient who was too ill or unwilling to participate and for whom the family/caregiver was unavailable, who was unavailable to be interviewed despite two attempts due to tests or procedures, transferred to another service or already discharged was excluded.
Medication History Interview
Prior to interviewing the patient, the study pharmacist reviewed the patient’s EMR and recorded the physician-obtained medication history, admission medication orders and the patient’s demographic information. A comprehensive interview with the patient and/or their caregiver was then conducted by the study pharmacist to obtain the patient’s current medication regimen. The study pharmacist inquired about all prescriptions, investigational therapies, over-the-counter medications, vitamins, herbals and any other products used to supplement the patient’s health. Other sources of information included the patient’s prescription bottle labels, self-prepared medication lists and/or consultation with community pharmacies. If the patient was previously hospitalized or cared for by a hospital or university-affiliated outpatient physician utilizing the EMR system within their clinic, available discharge summaries and outpatient medication lists were also reviewed.
Reconciliation of Medication Histories and Admission Medication Orders
Study pharmacist-obtained medication histories were compared with hospital physician-obtained medication histories and admission medication orders. Progress notes and changes made to patients’ medication orders since admission were reviewed to identify intentional discrepancies (e.g., formulary substitutions or modifications to pre-admission medications in response to a patient’s clinical status). The prescribing physician was then contacted regarding remaining unexplained discrepancies. Clarifications of unexplained discrepancies resulting in order changes were considered medication errors. This restrictive error definition should be more clinically meaningful as changes would be deemed appropriate to incorporate into patients’ treatment plans.
All medication results reported are for prescription medications only. Over-the-counter medications and herbals were excluded from analysis, although aspirin taken for cardiovascular purposes was classified as a “prescription” medication for analysis, similar to other published studies.2
Classification of Medication Errors and Potential Harm Assessment
Medication errors were classified by drug class and type of error: omission of a pre-admission prescription medication, incorrect addition of a medication not part of the patient’s pre-admission regimen (commission), different dose, different route and different frequency or different medication (within the same drug class). Each medication error was rated for its potential to cause harm during hospitalization if the error had not been identified and corrected. The National Coordinating Council for Medication Error Reporting and Prevention (NCC MERP) Index for Categorizing Medication Errors was adapted and utilized for rating potential harm.15,16
This nationally recognized NCC MERP harm level taxonomy was chosen because it is widely utilized by hospitals participating in the largest adverse drug event reporting system developed by the United States Pharmacopeia (USP).17
NCC MERP criteria were collapsed to group errors into three categories: (1) no potential harm (NCC MERP category C); (2) monitoring or intervention potentially required to preclude harm (NCC MERP category D); (3) potential harm (NCC MERP categories E and above).5
Ratings of potential
rather than actual harm are based on face validity only. The two study pharmacists collaboratively rated each medication error for potential harm followed by blinded, independent review by one of two board-certified internists. Pharmacist-physician harm ratings were then analyzed to determine inter-rater reliability of harm ratings across the three categories. There was a high overall initial agreement rate between pharmacist and physician ratings (Cohen’s kappa
0.84). Remaining disagreements were independently re-rated by the second board-certified physician to obtain the final harm rating.
Risk Factor Interview
Following the medication interview, the study pharmacist continued with further interview questions to identify risk factors including the number of prescribing physicians involved in the patient’s pre-hospitalization care, number of pharmacies utilized to fill prescriptions and recent changes (additions, deletions or modifications) within the last month to their medications. Study pharmacists also inquired whether patients’ medication bottles and/or medication lists were presented to the health care team upon hospitalization. Study patients lacking at least one prescription medication prior to hospitalization or patients admitted from a nursing home or rehabilitation facility where medications were managed by health care professionals were not evaluated.
Patient Medication Error Risk Factors
For all study patients, demographic factors analyzed for their association with medication errors included patients’ age, sex, race and ethnicity, and LEP, if applicable. Measures of potential clinical and severity of illness factors included the number of home medications, Medicare Diagnosis-Related Group (DRG) case mix index weight, length of stay and whether the patient was transferred to the intensive care unit during hospitalization. Finally, we controlled for whether the admission was to a hospitalist or teaching (resident care) service.
For study patients with complete risk factor interviews, chi-square tests were used to determine the significance of categorical variables and t-tests for continuous variables. Multiple logistic regression analyses were estimated for the combined likelihood of errors rated as either potentially requiring additional monitoring or intervention to preclude harm, or errors rated as potentially harmful. Controlling for the same clinical and demographic variables described above, regression models tested the significance of patients’ multiple pharmacy use, whether multiple physicians were involved in the patient’s pre-hospitalization care, history of recent medication or dosage changes, and whether the patient presented a medication list or bottles on admission. SPSS software version 16 (SPSS Inc., Chicago, IL) was used for all statistical analyses. A p value
0.05 was considered statistically significant.