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Analytical requirements , Free-drug concentrations

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  253-254

2026-10-19

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Analytical requirements

Free-drug concentrations

Free-drug concentrations, as indicated above, may be determined by measuring drug concentrations in a plasma ultrafiltrate obtained by centrifugation of plasma through an ultrafiltration membrane with a molecular weight cut-off of approximately 30 000 a.m.u., by equilibrium dialysis, or by ultracentrifugation. The three separation methods usually give similar results, although systematic differences have been reported and it is advisable to compare the results of two or more techniques when validating a new method. Ultrafiltration is often preferred in the clinical setting as it can be completed more rapidly than the other methods. Where drug binding to protein is temperature dependent, careful control of temperature during the separation step is essential. Monitoring of free drug concentration undoubtedly provides better clinical information than total concentration monitoring, but the increased methodological complexity and time required have limited its widespread application.