Liquid-chromatographic measurement of cyclosporin A and its metabolites in blood, bile, and urine.

Using solid-phase extraction columns and "high-performance" liquid-chromatographic (HPLC) analysis, we could determine cyclosporin A and nine of its metabolites in blood, bile, and urine. To facilitate calculations of concentrations of cyclosporin A and its metabolites from the chromatograms, we used cyclosporin D as internal standard. For the HPLC analysis we used two sequential 250-mm analytical columns filled with reversed-phase octyl (C8) sorbent, eluting with a concave gradient of water, adjusted to pH 3.0 with phosphoric acid, and acetonitrile. Peaks were detected at 205 nm. For characterization of the chromatographic peaks, we isolated, by semi-preparative HPLC, 32 fractions representing peaks potentially related to cyclosporin A metabolites and re-injected them into the HPLC system under the same conditions as authentic cyclosporin A metabolites. Analytical recovery was 70-80%. The inter-assay CV for bile was 7.2%, for urine 12.3%. The method was used for routine monitoring of cyclosporin A and its metabolites.