MONITORING TRICYCLIC ANTIDEPRESSANT CONCENTRATIONS IN SERUM BY FLUORESCENCE POLARIZATION IMMUNOASSAY COMPARED WITH GAS-CHROMATOGRAPHY AND HPLC

The fluorescence polarization immunoassay (FPIA) developed by Abbott t o diagnose intoxication with tricyclic antidepressants was adapted for therapeutic drug monitoring and validated with chromatographic method s to investigate its potential for this use. We compared serum concent rations of tricyclic antidepressants in vivo and in vitro obtained by FPIA with those by gas chromatography and HPLC. For amitriptyline, imi pramine, clomipramine, and doxepin, the detection limit of the FPIA wa s 72, 71, 64, and 72 nmol/L (similar to 20 mu g/l), respectively; that by gas chromatography was 18, 18, and 16 nmol/L (similar to 5 mu g/L) for amitriptyline, imipramine and clomipramine, respectively; with HP LC the lower limit of detection for doxepin was 36 nmol/L (10 mu g/L), The intra- and interassay CVs ranged from 3% to 6%. In patients being treated with amitriptyline, imipramine, clomipramine, and doxepin, at steady-state the correlation coefficients between FPIA and GC/HPLC re sults for split samples were 0.95, 0.92, 0.90 and 0.70, respectively. However, the slopes were close to unity only for amitriptyline and dox epin, being 0.6 for imipramine and 1.9 for clomipramine.