Cardiovascular event rates in atorvastatin patients versus patients switching from atorvastatin to simvastatin

Statin dose, adherence, and cardiovascular (CV) outcomes are important factors when considering switching statin therapies. The objective of the study was to compare CV event rates and risk in managed care patients receiving atorvastatin versus those switched to simvastatin from atorvastatin.

Patients 18-64 years, with ≥3 continuous pharmacy claims for atorvastatin between 1/1/05-11/30/07 and ≥12 months pre- and ≥3 months post-index continuous eligibility were identified using HealthCore Integrated Research Database (HIRD). Patients were stratified into two cohorts: one continued atorvastatin without interruption and the other switched to simvastatin. Patients were matched 1:10 (continue atorvastatin/switch simvastatin) on five variables, excluding lipid parameters due to limited data availability. Descriptive statistics were reported for sample characteristics. A multivariate Cox proportional hazards model was developed to evaluate adjusted CV risk.

In total 73,960 atorvastatin patients and 7396 simvastatin-switch patients were analyzed. The mean age was 54 ± 7 years (both cohorts). Mean follow-up was 440 days for atorvastatin patients and 237 days for simvastatin-switch patients. Mean dose and therapy duration for atorvastatin was 20 mg and 321 days compared with 33 mg and 195 days for simvastatin-switch, respectively. Of the simvastatin-switch patients, 32% were switched to a less potent simvastatin dose (<2× prior atorvastatin dose). After adjusting for demographic/clinical characteristics, no significant differences were found in CV risk between cohorts.

Limitations include use of administrative claims data without lipid level laboratory results data and the length of follow-up which may not have been sufficient to demonstrate significant differences in event rates between groups.

In this managed care population, no significant differences were found in risk of CV events among patients switching to simvastatin compared to patients continuing atorvastatin. Switched patients may differ from controls for reasons not captured in the database.