Analysis of whole-blood cyclosporin g by liquid chromatography in renal transplant recipients

Cyclosporin G (CsG) is less nephrotoxic than Cyclosporin A (CsA) and is undergoing clinical trials for use as an immunosuppressive agent after renal transplantation. In this study, CsG was measured by a rapid high‐performance liquid chromatography (HPLC) technique in blood samples (n=107) received from renal transplant recipients. The HPLC assay proved to be analytically suitable in that it was sensitive, linear, and precise and had high recovery (102%). However, interference was observed from some potentially co‐administered drugs such as calcitriol, ferrous sulfate, hydrazaline, and minoxidil. The HPLC assay for CsG correlated well with a FPIA (Abbott TDx), FPIA = 0.964 (HPLC) + 33.59, r = 0.9819, Sy/x = 36.66 for patients receiving a low dose of CsG (5 mg/kg/day) and a high dose (10 mg/kg/day). Furthermore, the HPLC technique was capable of measuring predictable CsG concentrations when the drug was tapered to lower doses at various stages of the 16 week clinical trial. The HPLC for CsG has the further advantage that the same system and mobile phase can be used to measure CsA while using CsC as the interval standard.