Switch-backs associated with generic drugs approved using product-specific determinations of therapeutic equivalence.

Purpose US Food and Drug Administration approval for generic drugs relies on demonstrating pharmaceutical equivalence and bioequivalence; however, some drug products have unique attributes that necessitate product-specific approval pathways. We evaluated rates of patients' switching back to brand-name versions from generic versions of four drugs approved via such approaches. Methods We used data from Optum LifeSciences Research Database to identify patients using a brand-name version of a study drug (acarbose tablets, salmon calcitonin nasal spray, enoxaparin sodium injection, and venlafaxine extended release tablets) or a control drug. We followed patients to identify switching to generic versions and then followed those who switched to identify whether they switched back to brand-name versions. We calculated switch and switch-back rates and used Kaplan-Meier and log-rank tests to compare rates between study and control drugs. Results Our cohort included 201 959 eligible patients. Brand-to-generic switch rates ranged from 66 to 106 switches per 100 person-years for study drugs and 80 to 110 for control drugs. Rates of switch-back to brand-name versions ranged from 5 to 37 among study drugs and 3 to 53 among control drugs. Switch-back rates were higher for venlafaxine vs. sertraline ( p < 0.01) and calcitonin vs. alendronate ( p = 0.01). Switch-back rates were lower for venlafaxine vs. paroxetine ( p < 0.01) and acarbose vs. nateglinide ( p < 0.01). Rates were similar for acarbose vs. glimepiride ( p = 0.97) and for enoxaparin vs. fondiparinux ( p = 0.11). Conclusion As compared to control drugs, patients were not more likely to systematically switch back from generic to brand-name versions of the four study drugs. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]