COMPETITIVE IMMUNOASSAY FOR CYCLOSPORINE USING CAPILLARY-ELECTROPHORESIS WITH LASER-INDUCED FLUORESCENCE POLARIZATION DETECTION

Frequent monitoring of immunosuppressive drug cyclosporine A, (CsA) in blood samples of tissue transplant patients is required in clinical p ractice because of the narrow therapeutic range between the immunosupp ressive effect and the toxic effect of this drug. We describe a compet itive immunoassay capillary electrophoresis (CE) with laser induced fl uorescence polarization detection method, which is rapid and sensitive for the determination of CsA. The method is based on the competitive immunochemical reaction between the analyte and fluorescent hapten (Cs A) with the antibody, CE separation of the antibody bound and free fl uorescent CsA, followed by the laser induced fluorescence polarizatio n detection (LIFP) of the fluorescent species. The method detection li mit is governed by the stability of the antibody-CsA complex rather t han by the detector noise. The use of post-column sheath flow cuvette LIFP detection resulted in excellent detection limit, typically 0.9 nM (or 9.10(-19) mol for 1 nl injection) of CsA. CsA in whole blood samp les from organ transplant patients were measured and results agreed we ll with those obtained by using a. standard fluorescence polarization immunoassay. Each determination took less than 3 min. The CsA metaboli tes AM9 and AM19 were also determined by using this technique, and the ir cross-reactivities with the antibody were 13% and 2%, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.