Aims: To evaluate the impact of adherence to statins on nonfatal coronary artery disease (CAD). Statins reduce cardiovascular morbidity and mortality after 1-2 years of continuous treatment. Studies have shown that <40% of patients take > or =80% of prescribed doses 1 year after starting therapy and that approximately half discontinue medication within 6 months of starting therapy.
Methods: A cohort of 20 543 patients was reconstructed using the Régie de l'assurance maladie du Québec databases. Patients aged 50-64 years, without cardiovascular disease, and newly treated with statins between 1998 and 2000 were eligible. A nested case-control design was used to study nonfatal CAD. Every case was matched with 20 randomly selected controls. The adherence level was defined as the percentage of the prescribed medication doses used over a specified period and classified as > or =90% or <90%. Rate ratios (RR) of nonfatal CAD were determined through conditional logistic regression adjusted for age, sex, socioeconomic status, diabetes and hypertension.
Results: The mean patient age was 58 years, 45% had hypertension and 19% had diabetes. Men represented 37% of the cohort. Among patients followed for >1 year, adherence of > or =90% was associated with fewer nonfatal CAD events (RR 0.81; 0.67, 0.97) compared with adherence <90%. In the multivariate model, male gender (RR 1.37; 1.16, 1.63), welfare recipients (RR 1.24; 1.04, 1.48), newly diagnosed hypertension (RR 3.54; 2.62, 4.77) and newly diagnosed diabetes mellitus (RR 1.97; 1.20, 3.24) were risk factors for CAD.
Conclusion: The incidence of nonfatal CAD events decreases when >90% of the prescribed medications is used over at least 1 year.