The long-term course of low-density lipoprotein cholesterol after initiation of statin treatment: retrospective database analysis over 3 years in health maintenance organization enrollees.

摘要

OBJECTIVES: Our primary objective was to obtain robust estimates of the low-density lipoprotein cholesterol (LDL-C) decrease from baseline over a long period (ie, 3 years) after initiation of statin treatment in a usual-care setting. Our secondary objective was to investigate the predictors of the LDL-C time course. METHODS: We retrospectively analyzed the data for a sample of enrollees in a health maintenance organization (HMO) who started statin treatment between October 1, 1995, and December 31, 1998. Using the HMO's claims database, we examined the LDL-C change from baseline (as measured at the prescribing physicians' discretion) and computed mean estimates every 6 months up to 3 years. We investigated potential predictors of the LDL-C time course (ie, age, sex, baseline LDL-C, previous treatment, prescribing physician's specialty, and most recent treatment) with a mixed model applied to longitudinal data. This model enabled us to impute missing data for all enrollees still being followed, including those who had stopped treatment, and to discuss the robustness of our findings. We applied 2 methods of imputation, assuming either of the following: (1) data were missing at random but could be estimated from the parameters in the mixed model, or (2) LDL-C returned to the baseline value > or =15 days after treatment cessation. RESULTS: We examined data from 3193 individuals. In most cases, the statin used was fluvastatin or pravastatin. The observed mean (95% CI) LDL-C decrease from baseline widened progressively from 23.6% (23.0%-24.3%) at 6 months to 28.0% (27.1%-28.9%) at 18 months and 30.2% (28.7%-31.7%) at 36 months after treatment initiation. These results remained robust after the imputation of missing data, with mean LDL-C reduction consistently >20% at each 6-month time point during the 3 years after treatment initiation. Variations as a function of baseline characteristics were limited (demographics) or explicable by extraneous factors (baseline LDL-C). There were predictable variations as a function of the most recent treatment. CONCLUSIONS: This analysis indicates a long-term reduction in LDL-C among a sample of HMO enrollees who initiated statin treatment in a usual-care setting. The results were robust after imputation of missing data, with mean decrease from baseline consistently >20% over 3 years. However, given the retrospective design of our study and the absence of a control group, we cannot determine how much of the decrease was attributable to treatment.