Topiramate is a newer anticonvulsant used to treat epi- lepsy, migraines, bipolar disorder, posttraumatic stress, and other conditions. Serum topiramate concentrations are measured to deter- mine optimal levels, address therapeutic failure or drug-drug inter- actions, and assess compliance. Two high-throughput assays for serum topiramate measurement were compared: the Seradyn fluo- rescence polarization immunoassay (FPIA) on an Abbott TDx/FLx instrument and a new immunoassay from ARK Diagnostics per- formed on an Olympus AU680 automated analyzer. Precision, lin- earity, limit of quantitation, carryover, spike recovery, and endogenous interferences were found to be acceptable for the ARK assay. These studies were complemented by comparison of 120 pa- tient samples analyzed using both methods. The ARK immunoassay performed comparably to FPIA with minimal difference in serum topiramate concentrations within the therapeutic range (2.0-20 mg/mL). A slight systematic discordance was observed at higher concentrations (greater than 30 mg/mL) with ARK immunoassay results being on average 6% higher than FPIA. Thus, the ARK immunoassay appears to provide acceptable analytical performance and comparability to FPIA; furthermore, the assay is compatible with high-throughput autoanalyzers.
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