Simplified Liquid-Chromotographic Analysis for Cyclosporin A, and Comparison with Radioimmunoassay

We describe a simplified isocratic “high-performance” liquid-chromatographic method for measuring a new im-munosuppressive drug, cyclosporin A, in biological fluids with use of its analogs cyclosporin C and cyclosporin D as internal standards. The method is reproducible and accu-rate and appears to be specific for cyclosporin A; the de-tection limit is 31.tg/L. The chromatographic measure-ments of the concentration of cyclosporin A in serum of patients receiving the drug were invariably lower than those by radioimmunoassay and the difference became more pronounced the greater the period of time after dosing. Because measurements of cyclosporin A in serum standards were almost identical with both techniques, the differences between the two sets of results for patients’ samples suggests that the radioimmunoassay is nonspe-cific and measures metabolites of cyclosporin A. Additional Keyphrases: drug assay. immunosuppressive drugs ‘ renal transplant cyclosporin