The primary aim of this BEEP2b study is to perform individual pharmacokinetic (PK) similarity testing of brand and generic AEDs in "probably GB" patients (N=12),who were selected on the basis of having GB-defining factors from the BEEP2a study, in order to confirm whether these factors are predictive of a generic brittle response to product switching. The study design involves a randomized, double-blind, multiple-dose, complete four-way replicate crossover design in which one brand and one generic will be compared in each patient from the patient's own AED regimen. Associated adverse events (i.e. seizures and side effects) will also be assessed. Bioequivalence (BE) will not be assessed. Rather, about nine AEDs are expected to be collectively evaluated. Generic brittleness anticipates that, for individual subjects, brand and generic may be the same or different, depending upon the underlying basis for generic brittleness. This exploratory research is focused on understanding individual patient attributes that contribute to GB, and is not focused on either product development or comparison of specific products.