Evaluation of Fluorescence Polarization Assays for Measuring Valproic Acid, Phenytoin, Carbamazepine and Phenobarbital in Serum

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The authors evaluated the fluorescence polarization (FP) assay on the COBAS INTEGRA 700 using COBAS INTEGRA reagent system cassettes for estimating the antiepileptic drugs valproic acid, phenytoin, carbamazepine, and phenobarbital in serum. The study comprised the determination of precision, method comparison performed against a conventional HPLC assay and linearity studies, according to the National Committee for Clinical Laboratory Standards (NCCLS) protocols. Precision results were well acceptable for all FP assays. Intra-assay coefficients of variation (CVs) were from 1.3% to 2.4% for valproic acid, from 0.8% to 2.8% for phenytoin, from 1.7% to 3.3% for carbamazepine, and from 1.3% to 2.3% for phenobarbital. Interassay CVs for these drugs ranged from 1.5% to 2.6%, from 2.9% to 6.5%, from 1.8% to 3.7% and from 1.5% to 3.2%, respectively. Results of the FP assays showed excellent correlation with those from HPLC:r = 0.99 for valproic acid, r = 0.98 for phenytoin, r = 0.98 for carbamazepine and r = 0.99 for phenobarbital. Linearity was satisfactory, with all CVs below the acceptable level. With the COBAS INTEGRA 700 analyzer FP assays are fully automated, which is less laborious and saves time compared with HPLC. Moreover, the fast measuring procedure is convenient in short turnaround time (STAT) analysis. It is an analytically reliable and rapid system, which can be used successfully for the therapeutic monitoring of antiepileptic drugs in serum.

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