Study Highlights

• The National Electronic Injury Surveillance System–Cooperative Adverse Drug Event Surveillance (NEISS-CADES) is an electronic surveillance system using data from 58 nonpediatric hospitals with a minimum of 6 beds and a 24-hour emergency department that contribute nationally representative data.
• Narrative descriptions of adverse events (clinician diagnoses and manifestations) are coded by the Medical Dictionary for Regulatory Activities, version 9.1.
• A surveillance case was defined as hospitalization after an emergency department visit by a person 65 years or older during 2007 to 2009 for a condition treated by a clinician specifically identified as being the result of a drug or drug-specific adverse event.
• Hospitalizations included inpatient admissions, observation admissions, and transfers to another hospital.
• Adverse events were categorized as allergic reactions, adverse events, or unintentional overdoses.
• Other effects included adverse effects from drug delivery methods or vaccine reactions.
• Excluded were intentional self-harm, drug abuse, therapeutic failures, and drug withdrawal.
• Outpatient visits for adults 65 years and older were identified from public-use data files for 2007 and 2008. Up to 8 prescriptions or over-the-counter medications, vaccines, and dietary supplements that were ordered or continued at each visit were recorded.
• The primary outcome was hospitalization after an emergency department visit for an ADE.
• Secondary outcome was hospitalization after an adverse event resulting from a "high-risk" drug, as defined by the 2011 Healthcare Effectiveness Data and Information Set (HEDIS).
• On the basis of 12,666 cases, an estimated 265,802 emergency department visits for an ADE occurred annually from 2007 through 2009 for adults 65 years and older.
• 37.5% of these visits required hospitalization, including 34.1% for inpatient admissions, 1.1% for transfers to another hospital, and 2.2% for observation admissions.
• Nearly half (48.1%) of the ADEs involved adults 80 years or older.
• The population rate of hospitalizations for ADEs was 3.5 times as high for those 85 years and older as for those 65 to 59 years old (4.6 vs 1.3 hospitalizations per 1000 persons).
• The risk remained elevated when stratified for the number of medications (0 - 4 vs ≥ 5 concomitant medications).
• The 5 most common therapeutic categories implicated were hematologic, endocrine, cardiovascular, central nervous system, and anti-infective agents.
• Most hospitalizations for hematologic agents were for hemorrhagic events (71.3%), and warfarin represented two thirds of hospitalizations.
• Nearly all hospitalizations for endocrine agents were related to hypoglycemia (94.6%), and two thirds of these hospitalizations involved neurologic symptoms such as loss of consciousness.
• The 4 most commonly implicated drugs were warfarin (33.3%), insulins (13.9%), oral antiplatelet agents (13.3%), and oral hypoglycemic agents (10.7%).
• Together, these drugs accounted for 67.0% of all hospitalizations and remained most common when stratified by age.
• Nearly all hospitalizations involving warfarin, insulin, and hypoglycemic agents resulted from unintentional overdoses.
• Of hospitalizations implicating warfarin, 12.5% involved another drug, most often an antiplatelet agent.
• Only 1.2% of hospitalizations for ADEs involved a high-risk HEDIS medication, and 6.6% were attributed to Beers-criteria potentially inappropriate agents.
• The rates of warfarin- and insulin-related hospitalizations were at least 48 times as high as ADEs resulting from HEDIS high-risk medications.
• The authors concluded that warfarin, insulins, oral antiplatelet agents, and hypoglycemic agents accounted for two thirds of ADEs leading to hospitalizations and that these hospitalizations were more common among older patients.