COMPARISON OF PHENYTOIN AND CARBAMAZEPINE SERUM CONCENTRATIONS MEASURED BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY, THE STANDARD TDX ASSAY, THE ENZYME-MULTIPLIED IMMUNOASSAY TECHNIQUE, AND A NEW PATIENT-SIDE IMMUNOASSAY CARTRIDGE SYSTEM

Steady-state concentrations of phenytoin (PHT) and carbamazepine (CBZ) were measured by a novel patient-side immunoassay system with a singl e-use cartridge (Biotrack 516). The Biotrack determinations were perfo rmed in whole blood and extrapolated to serum on the basis of the hemo globin content. The results were compared with serum concentrations me asured by high-performance liquid chromatography (HPLC) or the standar d TDx and enzyme multiplied immunoassay (EMIT) techniques. A total of 222 samples from epileptic patients on PHT and 322 samples from patien ts on CBZ were analyzed. In the case of PHT there was a highly linear correlation [r = 0.985, y = 1.113x - 0.589; x = HPLC, y = Biotrack] be tween HPLC and the Biotrack system in the concentration range of 2.5-3 0 mu g/ml. In the case of CBZ, the correlation between HPLC and the Bi otrack system in the concentration range of 2.0-20 mu g/ml was somewha t lower [r = 0.931, y = 1.129x - 0.136; x = HPLC, y = Biotrack]. Compa rable results were also found for the correlation of the Biotrack syst em with the TDx assay or with the EMIT assay, respectively. Comedicati on had no influence, or only a minor influence (valproic acid), on the concentration of PHT and CBZ measured by the Biotrack system. Further more, the concentration of the metabolite carbamazepine-10, Il-epoxide had no influence on the concentration of CBZ measured by the Biotrack system. Since the automated cartridge system is simple, can be used r apidly, and is performed with only a few drops of blood, this techniqu e offers some advantages for routine clinical use, especially under ou tpatient conditions.