SUPERCRITICAL-FLUID CHROMATOGRAPHY FOR THERAPEUTIC DRUG-MONITORING OFIMMUNOSUPPRESSANTS - SELECTIVITY FOR CYCLOSPORINE-A, FK-506 (TACROLIMUS), AND RAPAMYCIN

Clinical monitoring of cyclosporine A (CsA) in whole blood is currentl y performed by either immunoassays or high-performance liquid chromato graphy. A new immunosuppressant, FK 506 - Tacrolimus, is currently und ergoing multi-centers clinical trial for liver transplant, while activ e research and clinical studies are being performed for another new im munosuppressant, rapamycin. The present study investigated their chrom atographic selectivities by supercritical fluid chromatography, in com parison to HPLC. Feasibility studies were performed for the analyses o f extracts of whole blood samples, after solid-phase extraction. SFC a nalyses were performed by using an open tubular SB-biphenyl capillary column, CO2 as the mobile phase, pressure programming from 100 to 300 atmospheres, separation temperature of 70 degrees C, and FID detection . CsA eluted after the internal standard CsD, while FK 506 tautomer el uted after FK 506. From the ''reversal'' of elution order as compared to reversed-phase LC, the selectivity of the above column with CO2 as the mobile phase was characterized as ''normal-phase HPLC-like''. Anal ysis of extracts of CsA patient's samples, and FK 506 spiked whole blo od samples showed that the current SFC procedure did not achieve suffi cient sensitivity limit for clinical therapeutic drug monitoring.