PURPOSE: We examined the preventability of adverse warfarin-related events and potential adverse warfarin-related events ("near misses") in the nursing home setting. METHODS: We performed a cohort study of all long-term care residents of 25 nursing homes (bed size range, 90-360) in Connecticut during a 12-month observation period. The total number of residents in these facilities ranged from 2946 to 3212 per quarter. There were 490 residents who received warfarin therapy. Possible warfarin-related incidents were detected by quarterly retrospective review of nursing home records by trained nurse abstractors. Each incident was independently classified by 2 physician-reviewers to determine whether it constituted a warfarin-related event, its severity, and its preventability. The primary outcome was an adverse warfarin-related event, defined as an injury associated with the use of warfarin. Potential adverse warfarin-related events were defined as situations in which the international normalized ratio (INR) was noted to be 4.5 or greater, an error in management was noted, but no injury occurred. We also assessed time in specified INR ranges per nursing home resident day on warfarin. RESULTS: Over the 12-month observation period, 720 adverse warfarin-related events and 253 potential adverse warfarin-related events were identified. Of the adverse warfarin-related events, 625 (87%) were characterized as minor, 82 (11%) were deemed serious, and 13 (2%) were life-threatening or fatal. Overall, 29% of the adverse warfarin-related events were judged to be preventable. Serious, life-threatening, or fatal events occurred at a rate of 2.49 per 100 resident-months; 57% of these more severe events were considered preventable. Errors resulting in preventable events occurred most often at the prescribing and monitoring stages of warfarin management. The percentages of time in the less than 2, 2 to 3, and more than 3 INR ranges were 36.5%, 49.6%, and 13.9%, respectively. CONCLUSIONS: The use of warfarin in the nursing home setting presents substantial safety concerns for patients. Adverse events associated with warfarin therapy are common and often preventable in the nursing home setting. Prevention strategies should target the prescribing and monitoring stages of warfarin management.

OBJECTIVE: To determine the prevalence of potential dosing errors of medication dispensed to children for 22 common medications. STUDY DESIGN: Using automated pharmacy data from 3 health maintenance organizations (HMOs), we randomly selected up to 120 children with a new dispensing prescription for each drug of interest, giving 1933 study subjects. Errors were defined as potential overdoses or potential underdoses. Error rate in 2 HMOs that use paper prescriptions was compared with 1 HMO that uses an electronic prescription writer. RESULTS: Approximately 15% of children were dispensed a medication with a potential dosing error: 8% were potential overdoses and 7% were potential underdoses. Among children weighing <35 >kg, only 67% of doses were dispensed within recommended dosing ranges, and more than 1% were dispensed at more than twice the recommended maximum dose. Analgesics were most likely to be potentially overdosed (15%), whereas antiepileptics were most likely potentially underdosed (20%). Potential error rates were not lower at the site with an electronic prescription writer. CONCLUSIONS: Potential medication dosing errors occur frequently in outpatient pediatrics. Studies on the clinical impact of these potential errors and effective error prevention strategies are needed.

OBJECTIVE: To examine various strategies for the identification of adverse drug events (ADEs) among older persons in the ambulatory clinical setting. DESIGN: A cohort study of Medicare enrollees (n = 31,757 per month) receiving medical care from a large multispecialty group practice during a 12-month observation period (July 1, 1999 through June 30, 2000). MEASUREMENTS: Possible drug-related incidents occurring in the ambulatory clinical setting were detected using signals from multiple sources. RESULTS: During the tracking period, there were 1,523 identified ADEs, of which 421 (28%) were considered preventable. Across all sources, 23,917 signals were found; 12,791 (53%) were potential incidents that led to review of a patient's medical record and 2,266 (9%) were presented to physician reviewers. Although the positive predictive value (PPV) for reports from providers was high compared with other sources (54%), only 11% of the ADEs and 6% of the preventable ADEs were identified through this source. PPVs for other sources ranged from a low of 4% for administrative incident reports to a high of 12% for free-text review of electronic notes. Computer-generated signals were the source for 31% of the ADEs and 37% of the preventable ADEs. Electronic notes were the source for 39% of the ADEs and 29% of the preventable ADEs. There was little overlap in the ADEs identified across all sources. CONCLUSION: Our findings emphasize the limitations of voluntary reporting by health care providers as the principal means for detection of ADEs and suggest that multiple strategies are required to detect ADEs in geriatric ambulatory patients.

OBJECTIVES: To gather information on patient-level factors associated with risk of adverse drug events (ADEs) that may allow focus of prevention efforts on patients at high risk. DESIGN: Nested case-control study. SETTING: Large multispecialty group practice in New England. PARTICIPANTS: All Medicare enrollees cared for by a multispecialty group practice during 1 year (N=30,397 person-years from July 1, 1999, through June 30, 2000). For each patient with an ADE, a control was randomly selected. MEASUREMENTS: Data were abstracted from medical records on age, sex, comorbidities, and medication use at the time of the event. RESULTS: ADEs were identified in 1,299 older adults. Independent risk factors included being female and aged 80 and older. There were dose-response associations with the Charlson Comorbidity Index and number of scheduled medications. Patients taking anticoagulants, antidepressants, antibiotics, cardiovascular drugs, diuretics, hormones, and corticosteroids were at increased risk. In the analysis of preventable ADEs, the dose-response relationship with comorbidity and number of medications remained. Patients taking nonopioid analgesics (predominantly nonsteroidal antiinflammatory drugs and acetaminophen), anticoagulants, diuretics, and anti-seizure medications were at increased risk. CONCLUSION: Prevention efforts to reduce ADEs should be targeted toward older adults with multiple medical conditions or taking multiple medications, nonopioid analgesics, anticoagulants, diuretics, and antiseizure medications.

CONTEXT: Adverse drug events, especially those that may be preventable, are among the most serious concerns about medication use in older persons cared for in the ambulatory clinical setting. OBJECTIVE: To assess the incidence and preventability of adverse drug events among older persons in the ambulatory clinical setting. DESIGN, SETTING, AND PATIENTS: Cohort study of all Medicare enrollees (30 397 person-years of observation) cared for by a multispecialty group practice during a 12-month study period (July 1, 1999, through June 30, 2000), in which possible drug-related incidents occurring in the ambulatory clinical setting were detected using multiple methods, including reports from health care providers; review of hospital discharge summaries; review of emergency department notes; computer-generated signals; automated free-text review of electronic clinic notes; and review of administrative incident reports concerning medication errors. MAIN OUTCOME MEASURES: Number of adverse drug events, severity of the events (classified as significant, serious, life-threatening, or fatal), and whether the events were preventable. RESULTS: There were 1523 identified adverse drug events, of which 27.6% (421) were considered preventable. The overall rate of adverse drug events was 50.1 per 1000 person-years, with a rate of 13.8 preventable adverse drug events per 1000 person-years. Of the adverse drug events, 578 (38.0%) were categorized as serious, life-threatening, or fatal; 244 (42.2%) of these more severe events were deemed preventable compared with 177 (18.7%) of the 945 significant adverse drug events. Errors associated with preventable adverse drug events occurred most often at the stages of prescribing (n = 246, 58.4%) and monitoring (n = 256, 60.8%), and errors involving patient adherence (n = 89, 21.1%) also were common. Cardiovascular medications (24.5%), followed by diuretics (22.1%), nonopioid analgesics (15.4%), hypoglycemics (10.9%), and anticoagulants (10.2%) were the most common medication categories associated with preventable adverse drug events. Electrolyte/renal (26.6%), gastrointestinal tract (21.1%), hemorrhagic (15.9%), metabolic/endocrine (13.8%), and neuropsychiatric (8.6%) events were the most common types of preventable adverse drug events. CONCLUSIONS: Adverse drug events are common and often preventable among older persons in the ambulatory clinical setting. More serious adverse drug events are more likely to be preventable. Prevention strategies should target the prescribing and monitoring stages of pharmaceutical care. Interventions focused on improving patient adherence with prescribed regimens and monitoring of prescribed medications also may be beneficial.