Study to Evaluate Serum Free Thyroxine (FT4) and Free Triiodothyronine (FT3) Measurements for Subjects Treated With Eslicarbazeine Acetate (ESL)

Part 1 of the study will enroll a minimum of 30 male and female subjects who have received at least 1200 mg once daily (QD) ESL over a minimum 6-week period (ESL-exposed subjects). Subjects, who meet study eligibility requirements and provide written consent, will provide blood samples for measurement of thyroid hormones, thyroxine binding globulins (TBG), serum pregnancy (female subjects of childbearing potential 1only), thyroid peroxidase (TPO) antibodies, and ESL metabolites (eslicarbazepine and (R)-licarbazepine). Optional blood samples will be requested from subjects in Part 1 who provide genetic consent and are eligible to participate (as controls) in a separate rash registry protocol. These samples will be tested for HLA typing, genetic ancestry, and viral titers (including human herpes virus \[HHV\]-6, HHV-7, and Epstein-Barr virus \[EBV\]). ESL metabolites will be determined by a validated liquid chromatography- tandem mass spectrometry (LC-MS/MS) assay. Levels of FT4 and FT3 in ESL-exposed serum will be assayed using the automated kit assay (Roche Cobas ECLIA kits FT4 II and FT3 III) and Equilibrium Dialysis (ED) method. FT4 and FT3 results measured by both methods will be compared to evaluate potential assay differences. Serum TSH, TT4, TT3, and TBG in ESL treated subject samples will also be measured using automated kit assays. Part 2 of the study will enroll a minimum of 30 age (± 5 y) and gender-matched non-ESL exposed volunteers. Subjects, who meet study eligibility requirements and provide written consent, will provide a blood sample for measurement of thyroid hormones, TBG, serum pregnancy (female subjects of childbearing potential only), and TPO antibodies. Serum samples obtained from non-ESL exposed subjects will be split into 4 aliquots, one aliquot will be used as the control blank (unspiked) and the rest spiked with 3 levels (high, low, and a concentration representative of therapeutic levels also called middle) of eslicarbazepine (range approximately 5 to 18 μg/mL) and (R)-licarbazepine (range approximately 0.5 to 1.8 μg/mL). The low concentration for spiking the non-ESL exposed samples will be approximately 1 standard deviation (SD) below Cavg associated with the 800 mg dose in chronic use in the epilepsy population and the high concentration for spiking will be approximately 1 SD above Cavg associated with the 1200 mg dose. After sample is spiked with eslicarbazepine and (R)-licarbazepine, serum FT4 and FT3 will be measured by the automated kit assay method, as well as ED method. FT4 and FT3 measured in non-spiked and spiked volunteer samples will be compared to detect potential in vitro artifacts. Serum TSH, TT4, TT3, and TBG in non-spiked and spiked volunteer samples will also be measured using automated kit assays.