Association between short-term effectiveness of statins and long-term adherence to lipid-lowering therapy

Purpose. The relationship between low-density lipoprotein (LDL) cholesterol reduction in the first 3 months of statin therapy and medication adherence during a 33-month follow-up period was studied. Methods. A retrospective cohort study was conducted among enrollees in a Southeastern managed care plan who started therapy with atorvastatin, fluvastatin, lovastatin, pravastatin, or simvastatin between October 1999 and August 2001, were enrolled for >= 12 months before and >= 6 months after treatment initiation, and had at least one LDL cholesterol measurement in the year before and 4-12 weeks after the start of therapy. Patients were followed up via electronic pharmacy and medical records for up to 33 more months. The follow-up period was divided into 3-month intervals; patients were considered adherent if statin therapy was available >= 80% of the time. A generalized linear model for repeated measures quantified the association between change in LDL cholesterol at 4-12 weeks and medication adherence in subsequent intervals, adjusting for demographic, clinical, and health-service-use variables. Results. The final sample consisted of 9510 patients. Medication adherence decreased significantly over time: 59%,40%,34%, and 21% of patients were adherent at 3, 6, 12, and 36 months, respectively. Mean +/- S.D. LDL cholesterol reduction at 12 weeks was 28.9% +/- 19.9%. The relative LDL cholesterol reduction at 12 weeks was significantly and independently associated with subsequent medication adherence: Compared with subjects in the first quartile of LDL cholesterol reduction, those in quartiles 2,3, and 4 were more likely to be adherent in any subsequent interval (adjusted odds ratio [95% confidence interval], 1.26 (1.12-1.42], 1.25 [1.11-1.401, and 1.15 (1.02-1.29], respectively). Other independent predictors of adherence in months 4-36 included adherence during the initial three months of therapy, age, and recent history of coronary revascularization. Conclusion. Greater reduction in LDL cholesterol levels during the first three months of statin therapy was associated with greater adherence to lipid-lowering drug therapy.