Abstract
Purpose: Formulary changes involving statins have become common following the availability of generic simvastatin. While providing drug cost savings, there are concerns that mandatory formulary conversion may result in poor adherence and less LDLc goal attainment. Previous studies with large health maintenance organizations or government health systems have demonstrated successful outcomes with statin conversion. In 2006, a Medicaid health plan removed atorvastatin from their formulary and encouraged simvastatin or simvastatin/ezetimibe use. Minimal patient and provider guidance was provided in advance. The purpose of this project was to study the impact of this formulary change on treatment, average LDLc and treatment goal attainment. Methods: This retrospective, parallel group study was approved by the institutional review board. Patients seen in a family medicine teaching center, who switched from atorvastatin in 2006, were included. Patients from the Medicaid health plan with the formulary change were assigned to the study group. Control group patients were from other plans, and made the same medication change during the study period. Patients who did not have a follow-up visit with laboratory testing were excluded in some analyses. Endpoints included LDLc, LDLc goal attainment, accuracy of dosage conversion, laboratory assessments following medication changes, health service utilization, and adverse effects. Descriptive statistics were used to summarize findings and inferential statistics were used to evaluate differences between groups (paired students West, chi-square, and Z-test of proportions). The level of significance for all tests was a two-tailed P value less than 0.05. Results: Forty patients (31 study, 9 control) were available for full analysis. Patients were changed to simvastatin (n=28) and simvastatin/ezetimibe (n=12). No significant difference was found between mean LDLc (116.7 mg/dL + 38.2) at baseline, compared to mean LDLc (106.3 mg/dL + 37.4) post-conversion. No significant difference was found between goal attainment at baseline (69.7%), compared to goal attainment post-conversion (69.2%). We observed problems with appropriate statin dose conversion; the simvastatin dose was lower than pre-conversion atorvastatin in 12 (42.8%) of patients and the simvastatin/ezetimide dose was higher than pre-conversion atorvastatin in 6 (50%) of patients. This difference was statistically significant (p<0.001). These patterns persisted when controlled for preconversion LDLc. Due to a small number of control patients we were unable to compare appropriate dose conversions between groups. There were no adverse effects noted. Conclusion: Patients who underwent mandated statin formulary changes were commonly switched to doses of the new medication that were not considered clinically equivalent to previous doses. This difference persisted when considering pre-switch LDL. In this small sample these prescribing errors regarding appropriate dosage conversion did not adversely affect LDLc levels or LDLc goal attainment.