Ambulatory Care Visits for Treating Adverse Drug Effects in the United States, 1995-2001

Background: Adverse drug events (ADEs) are a well-recognized patient safety concern, but their magnitude is unknown. Ambulatory visits for treating adverse drug effects (VADEs) as recorded in national surveys offer an alternative way to estimate the national prevalence of ADEs because each VADE indicates that an ADE occurred and was serious enough to require care. Methods: A nationally representative sample of visits to physician offices, hospital outpatient departments, and emergency departments was analyzed. VADEs were identified as the first-listed cause of injury. Results: In 2001, there were 4.3 million VADEs in the United States, averaging 15 visits per 1,000 population. VADE rates at physician offices, hospital outpatient departments, and hospital emergency departments were at 3.7, 3.4, and 7.3 per 1,000 visits, respectively. There was an upward trend in the total number of VADEs from 1995 to 2001 (p < .05), but the increases in VADEs per 1,000 visits and per 1,000 population were not statistically significant. VADEs were lower in children younger than 15 and higher in the elderly aged 65-74 than in adults aged 25-44 (p < .01) and were more frequent in females than in males (p < .05). Discussion: Although methodologically conservative, the study suggests that ADEs are a significant threat to patient safety in the United States.