Abstract
Theophylline concentration of plasma from asthmatic patients was determined by newly developed substrate-labeled fluorescent immunoassay with monoclonal antibody (MC-SLFIA method). The results were compared with those obtained by high-performance liquid chromatography (HPLC) and substrate-labeled fluorescent immunoassay with rabbit antiserum (RA-SLFIA method).The coefficient of variation of 10 replicate analysis by MC-SLFIA method using theophylline spiked samples (5μg/ml land 15μg/ml) was less than 5%. There was a good correlation of both determinations between MC-SLFIA method and HPLC (n=73, r=0.994, p<0.001). Cross reactivity of MC-SLFIA method was studied using 9 different theophylline analogous compounds and estimated to increase the measured theophylline concentration by 20% when added to normal human plasma containing 15μg/ml of the drug. The cross reactivity was relatively small such as 200μg/ml for caffeine and 1, 3-dimethyluric acid. These findings show that MC-SLFIA method is a good method for clinical theophylline level monitoring with low cross reactivity, especially to some theophylline metabolites.
