QUANTIFICATION OF THEOPHYLLINE IN HUMAN PLASMA BY REVERSED-PHASE ION-INTERACTION HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND COMPARISON WITH THE TDX FLUORESCENCE POLARIZATION IMMUNOASSAY PROCEDURE

A new method for the determination of theophylline (1,3-dimethyl-1 H-purine-2,6-dione) in human plasma is described, free from interference by theobromine (3,7-dimethyl-1H-purine-2,6-dione) and caffeine (1,3,7-trimethyl-1H-purine-2,6-dione). The method makes use of ion-interaction reversed-phase high-performance liquid chromatography (octylamine-orthophosphate being the interaction reagent and a C18 reversed-phase column the stationary phase) with spectrophotometric detection at 274 nm. The quantitative results obtained in the analysis of samples of plasma from patients undergoing treatment with theophylline were compared with those obtained for the same samples with the TDx fluorescence polarization immunoassay procedure (using the Abbot Therapeutic Drug Monitoring system), which is generally employed in hospitals and clinical laboratories. Statistical F-test and t-test for multiple samples were applied to the data obtained by the two methods. The results showed no significant difference between the two methods at the 95% confidence level.