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ABSTRACTBackground: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 samestatin (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. [ABSTRACT FROM AUTHOR]