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 > or =12 months before and > or =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 > or =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 [1.11-1.40], 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.