Solid-phase extraction and liquid chromatography for improved assay of cyclosporine in whole blood or plasma

In this simple, precise, accurate, and specific isocratic liquid chromatographic procedure for determining cyclosporine, the cyclosporine is extracted from 1 mL of whole blood or from plasma, with 500 micrograms of cyclosporin D added per liter as internal standard, by elution from a Bond-ElutTM C18 extraction column with 300 microL of a mixture of ethanol and tetrahydrofuran. A 100-microL aliquot of the eluate, injected onto a cyano-phase analytical column, is eluted with a mixture of acetonitrile and pH 7.0 phosphate buffer at a flow rate of 1.0 mL/min and at 50 degrees C. Detection is at 210 nm. The chromatography is complete in less than 14.0 min. The method can measure less than 10.0 micrograms/L. Analytical recovery of cyclosporine added to whole blood ranged from 99 to 109% for concentrations up to 2000 micrograms/L. Between-run CVs ranged from 6.4 to 6.6%. None of numerous drugs and steroids tested interfered. Results by radioimmunoassay exceeded by 20 to 350% those measured by the present method.