Cyclosporin: erythrocyte binding and an examination of its use to estimate unbound concentration

Area of Science:

• Pharmacology
• Nephrology
• Clinical Chemistry

Background:

• Cyclosporin A (CyA) exhibits saturable binding to erythrocytes.
• Erythrocyte concentration theoretically could estimate unbound CyA, potentially correlating better with patient response than total plasma levels.

Purpose of the Study:

• To evaluate the practical utility of measuring erythrocyte CyA concentration for estimating unbound CyA levels.
• To compare this method with existing estimation techniques in renal transplant patients.

Main Methods:

• Analysis of 139 blood samples from renal transplant patients undergoing CyA therapy.
• Measurement of erythrocyte and plasma CyA concentrations.
• Comparison of erythrocyte-based estimation with plasma unbound fraction estimation.

Main Results:

• The method of estimating unbound CyA via erythrocyte concentration was not superior to assuming a constant unbound fraction in plasma.
• Both estimation methods demonstrated insufficient precision for practical clinical application.

Conclusions:

• Estimating unbound Cyclosporin A concentration using erythrocyte levels is not currently a reliable clinical method.
• Direct measurement of unbound CyA or calculation using total plasma concentration and the unbound fraction are necessary for accurate assessment.