In randomized trials, low-dose (LD) and high-dose (HD) aspirin (ASA) are equally effective in reducing ischemic complications, but HD ASA is associated with an increased risk of bleeding in the setting of dual antiplatelet therapy after percutaneous coronary intervention (PCI). ASA dose after PCI varies across countries, but little is known about variation within the United States (US) and whether this variation can be explained by clinical characteristics of patients. We used enrollment data from the Dual Antiplatelet Therapy Study, a randomized trial designed to compare 12 versus 30 months of dual antiplatelet therapy after PCI, to quantify the variation in ASA dosing after PCI in the US subjects and assess the extent to which dose variability was attributable to patient characteristics. Of the 23,336 patients enrolled in the US, 28.0% were prescribed LD ASA at discharge after PCI. Patient characteristics explained 1.6% of total variance in ASA dose, whereas the study site accounted for 45.9% of the unexplained variability. The median odds ratio comparing sites was 5.05 (95% confidence interval 4.29 to 5.85), which was greater than any individual predictor of ASA dose. In conclusion, LD ASA after PCI in the US was used in a minority of patients, and heterogeneity in its selection was mainly influenced by the site of enrollment rather than patient characteristics. As HD ASA may be associated with adverse events in the setting of dual antiplatelet therapy, reducing local practice variation in the dose of ASA may be a target for quality improvement.
Trial registration: ClinicalTrials.gov NCT00977938.
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