Whole-blood cyclosporin G in renal transplant recipients determined by two immunoassays and liquid chromatography.

Cyclosporin G (CsG) is less nephrotoxic than cyclosporin A (CsA) and is undergoing clinical trials for use as an immunosuppressive agent after renal transplantation. Three assays for whole-blood CsA-HPLC, RIA (INCSTAR, Cyclo-Trac SP), and FPIA (Abbott TDx)--were adapted for use with CsG and were assessed for analytical suitability and to determine which assay was capable of deriving CsG values rapidly after transplantation. The assays were acceptable in terms of sensitivity, linearity, analytical recovery, and precision. When considering blood samples (n = 107) from renal transplant recipients receiving a low dose of CsG (5 mg/kg per day) and a high dose (10 mg/kg per day), we obtained the following correlation data: RIA = 0.974HPLC + 27.89 (r = 0.9798, Sy/x = 39.24); FPIA = 0.964HPLC + 33.59 (r = 0.9819, Sy/x = 36.66); and FPIA = 0.977RIA + 9.50 (r = 0.9894, Sy/x = 28.12). The FPIA of CsG is recommended as the most rapid method, although it is the most expensive. HPLC, RIA, and FPIA were capable of accurately deriving projected CsG concentrations at various stages of the clinical trial when the low- and high-dose regimes were tapered over a period of 16 weeks.