Cyclosporin A (Cya) in human plasma-containing interfering compounds was determined by high performance liquid chromatography (HPLC) after the plasma had been subjected to incubation with proteinase K. This hydrolytic enzyme did not hydrolyse the cyclosporins and was therefore an ideal aid in eliminating interfering peptides selectively. The use of Extrelut® as an extraction aid contributed much to higher yields of cyclosporins. Ethyl acetate, the extraction solvent used, gave less complex profiles on HPLC chromatograms than other solvents (eg diethyl ether and methanol) and contributed to a shorter chromatographic period per sample, an advantage in repetitive determinations.
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