A kinetic method for the determination of plasma protein binding of compounds unstable in plasma: Specific application to enalapril

• Published in: Journal of pharmaceutical and biomedical analysis Vol. 55; no. 3; pp. 385 - 390
• Main Authors: Wenlock, Mark C., Barton, Patrick, Austin, Rupert P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2011; Elsevier
• Subjects: Adsorption; Analysis; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; blood proteins; Blood Proteins - chemistry; Blood Proteins - metabolism; Centrifugation; charcoal; Charcoal - chemistry; Charcoal binding; chemical degradation; Clinical Laboratory Techniques - instrumentation; dextran; Dextrans - chemistry; Dialysis; Dogs; Drug Stability; Enalapril; Enalapril - chemistry; Enalapril - metabolism; Fundamental and applied biological sciences. Psychology; General pharmacology; Guinea Pigs; Humans; hydrolysis; In Vitro Techniques; Initial rates; Medical sciences; Pharmacology. Drug treatments; Piperazines - chemistry; Piperazines - metabolism; Plasma instability; Plasma protein binding; Protein Binding; Purines - chemistry; Purines - metabolism; Rats; Reproducibility of Results; Sildenafil Citrate; Sulfones - chemistry; Sulfones - metabolism; Time Factors; ultrafiltration; Verapamil - chemistry; Verapamil - metabolism; Warfarin - chemistry; Warfarin - metabolism; Charcoal binding; Plasma protein binding; Plasma instability; Enalapril; Initial rates; Biological fluid; Enzyme; Enzyme inhibitor; Kinetic method; Determination; Serum protein; Blood plasma; Peptidases; Binding protein; Peptidyl-dipeptidase A; Hydrolases; Peptidyl-dipeptidases; Antihypertensive agent; ACE inhibitor; Quantitative analysis; Charcoal
• ISSN: 0731-7085; 1873-264X; 1873-264X
• DOI: 10.1016/j.jpba.2011.02.006

Traditional methods for the determination of plasma protein binding (PPB), such as equilibrium dialysis and ultrafiltration, normally operate on a timescale ranging from tens of minutes to several hours and are not suitable for measuring compounds that have significant chemical degradation on this timescale. One such compound is enalapril. Although stable in human plasma enalapril is subject to rapid esterase-catalyzed hydrolysis in rat plasma. A method has been developed which allows the extent of rat PPB of enalapril to be determined from initial rates kinetics of the adsorption of the unstable compound to dextran coated charcoal (DCC). The method has been applied to stable compounds, and the results are consistent with those from traditional equilibrium dialysis experiments. The experimental method is simple to run, requires no specialized equipment, and can potentially be applied to other compounds that show instability in plasma where traditional experimental techniques are unsuitable.