Proteins pharmacokinetic analysis

Drug Levels in Plasma. Drug levels may also be measured in a clinical trial. Such levels are usually part of a pharmacokinetic analysis but also provide important safety data. This information would be particularly relevant in cases of suspected or actual drug overdosage, drug interactions, to correlate medicine levels with toxic events, or in other situations. It must be clarified whether free levels of the drug and/or the protein bound will be measured by the laboratory. 

It is possible to predict what happens to Vd when fu or fur changes as a result of physiological or disease processes in the body that change plasma and/or tissue protein concentrations. For example, Vd can increase with increased unbound toxicant in plasma or with a decrease in unbound toxicant tissue concentrations. The preceding equation explains why because of both plasma and tissue binding, some Vd values rarely correspond to a real volume such as plasma volume, extracellular space, or total body water. Finally interspecies differences in Vd values can be due to differences in body composition of body fat and protein, organ size, and blood flow as alluded to earlier in this section. The reader should also be aware that in addition to Vd, there are volumes of distribution that can be obtained from pharmacokinetic analysis of a given data set. These include the volume of distribution at steady state (Vd]SS), volume of the central compartment (Vc), and the volume of distribution that is operative over the elimination phase (Vd ea). The reader is advised to consult other relevant texts for a more detailed description of these parameters and when it is appropriate to use these parameters. 

Braeckman, R. (2000), Pharmacokinetics and pharmacodynamics of protein therapeutics, in Reid, R., Ed., Peptide and Protein Drug Analysis, Marcel Dekker, New York. 

Braeckman R (1999). Pharmacokinetics and Pharmacodynamics of Protein Therapeutics. In Rereid (ed.). Peptide and Protein Drug Analysis, University of British Columbia, Vancouver, B.C., pp. 633-639. 

LP James, Capparelli EV, Hinson JA, Dalvem TJ, Lee WM (2007) Pharmacokinetic analysis of acetaminophen protein adducts in adults with acute liver failure. Clin Pharmacol Ther 81 2 Smilkstein MJ, Knapp GL, Kulig KW, Rumack BH (1988) Efficacy of oral N-acetylcysteine in the treatment of acetaminophen overdose. Analysis of the national multicenter study (1976 to 1985). N Engl J Med 319 1557-1562... 

Urea Pharmacokinetics. Pharmacokinetics summarizes the relationships between solute generation, solute removal, and concentration in a patient s blood stream. In the context of hemodialysis, this analysis is most readily appHed to urea, which has, as a consequence, become a surrogate for other uremic toxins in the quantitation of therapy and in attempts to describe its adequacy. In the simplest case, a patient is assumed to have no residual renal function. Urea is generated from the breakdown of dietary protein, accumulates in a single pool equivalent to the patient s fluid volume, and is removed uniformly from that pool during hemodialysis. A mass balance around the patient yields the following differential equation ... 

Many process mixtures, notably fermentations, require sample preconcentration, microdialysis, microfiltration, or ultrafiltration prior to analysis. A capillary mixer has been used as a sample preparation and enrichment technique in microchromatography of polycyclic aromatic hydrocarbons in water.8 Microdialysis to remove protein has been coupled to reversed phase chromatography to follow the pharmacokinetics of the metabolism of acetaminophen into acetaminophen-4-O-sulfate and acetaminophen-4-O-glucu-ronide.9 On-line ultrafiltration was used in a process monitor for Aspergillus niger fermentation.10... 

An extensive retrospective analysis [11] examined various scahng approaches to the prediction of clinical pharmacokinetic parameters. In this analysis the most successful predictions of volume of distribution were achieved by calculating unbound fraction in tissues (/(,) of animals and assuming this would be similar in man. Volume of distribution was then calculated using measured plasma protein binding values and standard values for physiological parameters such as extracellular fluid and plasma volumes. The equation used was as follows ... 

Plasma protein binding is also an important parameter in the pharmacokinetic field. Frontal analysis combined with capillary zone electrophoresis (CZE-FA) (67-69) is a powerful technique for high-throughput assay, because it is relatively rapid and easy to automate, in comparison with conventional methods such as dialysis, ultrafiltration, and ultracentrifugation. Recently, we introduced the EKC approach with ionic CDs to frontal analysis for anionic drugs that cannot be analyzed by conventional CZE-FA (70). In this approach, ionic CDs work as an EKC pseudostationary not for proteins but for small solutes. 

Macek et al. [120] developed a method to quantitate omeprazole in human plasma using liquid chromatography-tandem mass spectrometry. The method is based on the protein precipitation with acetonitrile and a reversed-phase liquid chromatography performed on an octadecylsilica column (55 x 2 mm, 3 /im). The mobile phase consisted of methanol-10 mM ammonium acetate (60 40). Omeprazole and the internal standard, flunitra-zepam, elute at 0.80 0.1 min with a total rim time 1.35 min. Quantification was through positive-ion made and selected reaction monitoring mode at m/z 346.1 —> 197.9 for omeprazole and m/z 314 —> 268 for flunitrazepam, respectively. The lower limit of quantification was 1.2 ng/ml using 0.25 ml of plasma and linearity was observed from 1.2 to 1200 ng/ml. The method was applied to the analysis of samples from a pharmacokinetic study. 

Liu X, Smith BJ, Chen C, et al. Use of a physiologically based pharmacokinetic model to study the time to reach brain equilibrium an experimental analysis of the role of blood-brain barrier permeability, plasma protein binding, and brain tissue binding. J Pharmacol Exp Ther 2005 313(3) 1254—1262. 

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