Background: The study objective was to compare dose-equivalence, adherence and subsequent switch rates among patients recently switched from a branded to generic version of the same statin (generic substitution, GS) vs. those switched from branded statin to generic version of a different statin (therapeutic substitution, TS). Methods: In a retrospective cohort analysis among adult enrollees in over 90 US health plans, the authors identified adult patients who switched from a branded to generic statin from July-December 2006 (simvastatin became generic in June 2006). Patients were classified by type of statin switch: GS (e.g., branded simvastatin -> generic simvastatin), and TS (e.g., branded atorvastatin -> generic simvastatin). Demographic and clinical data were collected from claims before switch through 6 months follow-up. Separate outcomes of interest included proportion of patients that switched to a less potent daily dose, that switched back to previous branded statin after switch, and that were at least 80% adherent during the 6 months after initial switch. Significant predictors of each clinical outcome were identified using multivariable logistic regression models,adjusting for differences between groups in covariates and potential confounders. Results: The 6-month TS (n=3807) and GS (n=40,165) groups were generally similar demographically. Compared to GS, TS patients were significantly more likely to be switched to a less potent dose (26.2% vs. 0.5%, adjusted odds ratio [AOR] in patients with high-potency index medication 83.4, p<0.0001); 33% less likely to be adherent in the 6 months after switch (67.7% vs. 75.9%, AOR in patients with no switch in first 6 months follow-up=0.67, p<0.0001); and four times more likely to switch back to previous branded statin (11.3% vs. 2.9%, AOR 4.1, p<0.0001). Limitations: This study did not account for co-payment changes, lipid measurements, or changes in pill burden. Conclusions: While this study did not have data on why patients had TS (e.g., for cost or clinical reasons), TS was more likely to involve a subsequent disruption to statin therapy than GS. TS could potentially lead to adverse impacts on patients' outcomes, and should be studied further.
