Liquid-Chromatographic Determination of Cyclosporin A in Blood and Plasma

Abstract

Featured Article: Sawchuk RJ, Cartier LL. Liquidchromatographic determination of cyclosporin A in blood and plasma. Clin Chem 1981;27:1368 -71. 2 Shortly after the introduction of cyclosporin A in the late 1970s, much controversy surrounded the notion of a therapeutic range for this drug. Although evidence suggested a nephrotoxic range (1, 2 ), clinicians had little guidance as to what concentrations in blood or plasma should be maintained to ensure adequate immunosuppression. Indeed, questions surrounded the choice of plasma vs whole blood as the preferred matrix for monitoring patient response. There clearly was a need for a reliable, specific, and relatively rapid assay for cyclosporin A in biological matrices. Linda Cartier and I published this paper to describe such a method for the quantitfication of this drug in the blood and plasma of transplant patients.One of the factors contributing to the difficulty in identifying a therapeutic range for cyclosporin A was the large amount of variability observed in plasma concentrations of this peptide in a given patient receiving the same dose over an extended period of time. This intrapatient variability was explained by unpredictability in the absorption of the drug. Eventually, absorption variability was attributed in part to a significant "first-pass" metabolic effect related to hepatic and intestinal metabolism as the drug was absorbed into the systemic circulation. An additional factor was the limited and variable absorption of the drug from the dosage form available at that time. Circadian and food effects were also likely involved.In addition to these factors, however, another source of uncertainty appeared to exist in the routine monitoring of transplant patients receiving cyclosporin A. Because of the inherent properties of this cyclic peptide, its distribution between plasma and erythrocytes was dependent on the patient's hematocrit, the concentration of the drug in the blood sample, and how long the sample sat on the bench at room temperature before centrifugation. Recognition of this ex vivo redistribution of this immunosuppressive agent between the components of whole blood led to the idea that the drug concentration might be more reliably measured in whole blood, because this metric was not subject to the postsampling artifacts that contributed to the variability seen in the measurement of plasma concentrations.Transplant surgeons and clinicians who were treating patients with immunosuppressive therapy believed that cyclosporin exhibited a narrow therapeutic index and were aware of the difficulties in interpreting plasma concentrations. These healthcare professionals therefore sought a reliable analytic method for quantifying cyclosporin in whole blood. Responding to a request from our clinical colleagues at the University of Minnesota, we developed an HPLC method for the determination of whole blood concentrations of cyclosporin A.The analytical method we established involved solvent extraction with a backwash to remove lateeluting endogenous co...

Therapeutic and Toxicological Evaluations of Cyclosporine A Microspheres as a Treatment Vehicle for Uveitis in Rabbits

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