Several automated analytical systems for therapeutic drug monitoring (TDM) have been developed. In the present study, theophylline concentration in plasma was measured by the Biotrack 516 system for theophylline, a newly developed automated system based on the turbidimetric latex agglutination inhibition reaction, using whole blood samples obtained from 35 asthmatic patients receiving chronic theophylline therapy. The data were compared with those obtained by high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay (FPIA). Within-day and between-day precisions for the Biotrack system using blood samples obtained from nine patients ranged from 4.1 to 5.8% and from 2.0 to 6.2%, respectively. Comparison of this system with HPLC and FPIA methods indicated good correlation coefficients of >0.960, while the respective slope and intercept did not differ from unity and zero. No cross-reactivity of this system with the main metabolites of theophylline and caffeine was observed, thus indicating that the antibodies possess specificity for theophylline. These findings suggest that the Biotrack-516 system is a method that enjoys both accuracy and precision to the same degree as established methods and hence will prove useful in the routine monitoring of plasma theophylline concentrations.
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