Brand versus generic: addressing non-adherence, secular trends and non-overlap

Whereas generic drugs offer a cost-effective alternative to brand name drugs, regulators need a method to assess therapeutic equivalence in a post-market setting. We develop such a method in the context of assessing the therapeutic equivalence of immediate release venlafaxine, based on a large insurance claims data set provided by OptumLabs^®. To address this question properly, our methodology must deal with issues of non-adherence, secular trends in health outcomes and lack of treatment overlap due to sharp uptake of the generic drug once it becomes available. We define, identify (under assumptions) and estimate (using G-computation) a causal effect for a time-to-event outcome by extending regression discontinuity to survival curves. We do not find evidence for a lack of therapeutic equivalence of brand and generic immediate release venlafaxine.