Adverse drug events resulting from patient errors in older adults.

OBJECTIVES: To characterize the types of patient-related errors that lead to adverse drug events (ADEs) and identify patients at high risk of such errors. DESIGN: A subanalysis within a cohort study of Medicare enrollees. SETTING: A large multispecialty group practice. PARTICIPANTS: Thirty thousand Medicare enrollees followed over a 12-month period. MEASUREMENTS: Primary outcomes were ADEs, defined as injuries due to a medication, and potential ADEs, defined as medication errors with the potential to cause an injury. The subset of these events that were related to patient errors was identified. RESULTS: The majority of patient errors leading to adverse events (n=129) occurred in administering the medication (31.8%), modifying the medication regimen (41.9%), or not following clinical advice about medication use (21.7%). Patient-related errors most often involved hypoglycemic medications (28.7%), cardiovascular medications (21.7%), anticoagulants (18.6%), or diuretics (10.1%). Patients with medication errors did not differ from a comparison group in age or sex but were taking more regularly scheduled medications (compared with 0-2 medications, odds ratio (OR) for 3-4 medications=2.0, 95% confidence interval (CI)=0.9-4.2; OR for 5-6 medications=3.1, 95% CI=1.5-7.0; OR for >or=7 medications=3.3, 95% CI=1.5-7.0). The strongest association was with the Charlson Comorbidity Index (compared with a score of 0, OR for a score of 1-2=3.8, 95% CI=2.1-7.0; OR for a score of 3-4=8.6, 95% CI=4.3-17.0; OR for a score of >or=5=15.0, 95% CI=6.5-34.5). CONCLUSION: The medication regimens of older adults present a range of difficulties with the potential for harm. Strategies are needed that specifically address the management of complex drug regimens.

Risk factors for adverse drug events among older adults in the ambulatory setting.

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.