Generic and therapeutic statin switches and disruptions in therapy

ABSTRACT

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.

Key words: :

• Adherence
• Generic substitution
• Quality of care
• Statins

Acknowledgments

Declaration of interest: This study was sponsored by Pfizer Inc. R.H.C. and P.G. are employees of IMS Health, which received payment from Pfizer for research and consulting services associated with this manuscript. J.S.B. was an employee of IMS Health when this study was conducted. M.B.N. received an honorarium from Pfizer for consultation during the study and for development of this manuscript. M.B., K.A., and L.Z.L. are employees of Pfizer Inc. Editorial support was provided by Caitlin Rothermel and funded by IMS Health.