Abstract 14793: Variation in Aspirin Dose in Dual Antiplatelet Therapy After Percutaneous Coronary Intervention

Abstract

Introduction: 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 PCI. Aspirin dose after PCI varies across countries, but little is known about variation within the US and whether this variation can be explained by clinical characteristics of patients.

Methods: The Dual Antiplatelet Therapy (DAPT) Study is a randomized trial designed to compare 12 vs 30m of dual antiplatelet therapy after PCI. The study completed enrollment in July 2011 from 11 countries, and is currently in follow-up. Generalized linear mixed models accounting for clustering within sites were fitted separately for US and non-US subjects to identify predictors of LD-ASA (< 100 mg/day) at discharge. We quantified the variation in ASA dosing among sites and assessed the extent to which this was attributable to differences in patient characteristics.

Results: Among the 25,850 patients undergoing PCI in the DAPT Study, 28.5% and 94.1% were prescribed LD-ASA in the US and non-US subset. Within the US, there was extensive variation in discharge ASA dose between sites (Figure). Patient characteristics explained 1.7% of total variance in ASA dose, whereas study site explained 43.9%. The median odds ratio (MOR) comparing the use of LD-ASA among similar patients at 2 randomly selected US sites was 4.72 (95%CI 4.14 - 5.34). Similarly, predictors of LD-ASA in non-US patients explained 4.0% of variance, site explained 40.7% and MOR for site was 6.45 (95%CI 3.18 - 10.68).

Conclusion: Low dose ASA after PCI in the US was uncommon and heterogeneity in its selection was primarily attributable to site of enrollment rather than to patient characteristics. Large pragmatic trials, such as the DAPT Study, may identify targets for quality improvement, such as reducing local practice variation in dose and duration of medical treatments.