Underutilization of Aspirin Persists in US Ambulatory Care for the Secondary and Primary Prevention of Cardiovascular Disease

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To explore the relative priority assigned to aspirin and statins,we examined trends in the co-prescribing of the medications. For this series of analyses, the number of visits by patients with DM was relatively small and were therefore grouped with those with known CVD to compose the high-risk category. Both aspirin and statins were used more frequently when the other therapy was present; however, improvements over time were more evident for statin use among aspirin-treated patient visits than for aspirin use among statin-treated patients. Specifically, the proportion of visits by high-risk patients on aspirin while a statin was used declined modestly from 36.5% (24.9-48.2%) in 1993-1994 to 25.6% (20.1-31.1%) in 1999-2000, but then rebounded to 43.9% (35.1-52.8%) in 2003. In contrast, statin use among visits by high-risk patients on aspirin grew successively from 11.6% (7.4-15.7%) to 54.3% (45.7-63.0%). Of visits by intermediate-risk patients, the probability of aspirin use when on a statin increased from 6.0% (1.4-10.6%) in 1993-1994 to 33.8% (21.5-46.0%) in 2003, while the probability of statin use when on aspirin rose from 8.8% (2.2-15.3%) to 48.1% (35.2-61.0%).

The association of greater aspirin use with higher CVD risk was confirmed by multivariate logistic regression (see Table 1). After adjusting for patient visit characteristics and the number of medications reported, aspirin use was over four times as likely among visits by high-risk patients and approximately two times as likely among visits by patients with multiple risk factors as it was among low-risk patient visits. The odds ratio was marginally significant for the diabetic, intermediate-risk category. The significance of increases in aspirin use over time did not sustain in the multivariate logistic regression. As for patient visit characteristics, lower probability of aspirin use was found among 20- to 44-year-olds (versus those 45 years or older), women (versus men), visits to non-cardiologists (versus visits to cardiologists), return visits (versus first-time visits), and visits to private physician offices (versus visits to hospital outpatient departments). Finally, the probability of aspirin use was positively associated with the number of medications reported (odds ratio, 1.71; 99% CI 1.65-1.76).

Discussion

This study documents national trends in the probability of aspirin use by CVD risk category among patient visits to office-based physicians and hospital outpatient departments. Some improvements were observed over time in the use of aspirin for both the secondary and primary prevention of CVD. However, the magnitude of those improvements is minimal relative to the substantial gaps between clinical practice and evidence-based recommendations.

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