Evaluation of the Abbott TDx™ for the Stat Measurement of Phenobarbital, Phenytoin, Carbamazepine, and Theophylline

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Abstract
The Abbott TDx™ is a fully automated method for drug-level monitoring. The system consists of a competitive fluorescence polarization immunoassay performed by a microprocessor-controlled fluorometer with integral pipetting and data reduction systems. We evaluated the method for the stat measurement of phenobarbital (PHENO), phenytoin (PTN), carbamazepine(CARB), and theophylline (THEO). The threshold of detection is PHENO, 0.8 mg/L; PTN, 0.8 mg/L; CARB, 0.1 mg/L; and THEO, 0.4 mg/L. Between-run precision in the therapeutic range expressed as coefficient of variation is between 3.3% and 9.1% for all four drugs. Recovery of each drug from a variety of matrices was essentially 100%, with no significant interference by elevated levels of bilirubin, triglycerides, or hemoglobin. The TDx methods were correlated to established methods for 100 patient specimens: PHENO: Y(TDx) ; 0.95 (GLC) + 1.4 mg/L R ; 0.98 PTN: Y(TDx) ; 0.91 (GLC) + 1.1 mg/L R ; 0.99 CARB: Y(TDx) ; 0.91 (EMIT) + 0.4 mg/L R ; 0.98 THEO: Y(TDx) ; 0.93 (HPLC) + 0.5 mg/L R ; 0.99 The calibration stability is no shorter than one week (PTN) and as long as five weeks (CARB). The analytic system is an accurate, precise, and highly stable method for the stat measurement of these four drugs.

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