Reversed-phase high-performance liquid chromatography determination of cyclosporin in human blood

A high-performance liquid chromatographic (HPLC) method for determination of cyclosporin A (CyA) in blood, using cyclosporin D (CyD) as internal standard, is described. The method is specific, precise, reproducible, accurate, and isocratic, and it requires no derivatization. It is more rapid than previously described methods. Its detection limit is 25 ng/ml, suitable for quantitation of the drug at clinically observed concentrations. No interference was found by any of the other commonly coadministered drugs tested. Comparison of measurements in patients' blood with radioimmunoassay (RIA) results showed lower estimates by the chromatographic technique. Because measurements of the drug in blood banks spiked with pure CyA were similar with the two techniques, the nonspecificity of RIA, probably related to cyclosporin metabolites, was demonstrated. Because the chromatographic technique is simple, it should be preferred to RIA in therapeutic drug monitoring.