Topiramate is a newer anticonvulsant used to treat epilepsy, migraines, bipolar disorder, posttraumatic stress, and other conditions. Serum topiramate concentrations are measured to determine optimal levels, address therapeutic failure or drug-drug interactions, and assess compliance. Two high-throughput assays for serum topiramate measurement were compared: the Seradyn fluorescence polarization immunoassay (FPIA) on an Abbott TDx/FLx instrument and a new immunoassay from ARK Diagnostics performed on an Olympus AU680 automated analyzer. Precision, linearity, 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 patient 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 μg/mL). A slight systematic discordance was observed at higher concentrations (greater than 30 μg/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.
From the Toxicology and Drug Monitoring Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN.
Received for publication August 4, 2009; accepted October 6, 2009.
Reagents for the ARK immunoassay were provided free of charge and costs associated with the ARK immunoassay were funded by ARK Diagnostics. The remainder of the study was supported by Mayo Clinic internal funds.
Correspondence: Christine L. H. Snozek, PhD, Hilton 730, Mayo Clinic, 200 1st Street Southwest, Rochester, MN 55905 (e-mail: firstname.lastname@example.org).