Musteata Florin Marcel, Pawliszyn Janusz, Qian Mark G, Wu Jing-Tao, Miwa Gerald T
Department of Chemistry, University of Waterloo, Ontario, Canada.
J Pharm Sci. 2006 Aug;95(8):1712-22. doi: 10.1002/jps.20558.
The plasma protein binding of drugs has been shown to have significant effects on the quantitative relationship between clinical pharmacokinetics and pharmacodynamics. In many clinical situations, measurement of the total drug concentration does not provide the needed information concerning the unbound fraction of drug in plasma, which is available for pharmacodynamic action. Therefore, the accurate determination of unbound plasma drug concentrations is important in understanding drug action. Many methodologies exist for determining the extent of plasma protein binding, but different methods produce a rather wide range of results for the same compound at the same concentration level. The solid phase microextraction (SPME) method reported in the present study attempts to eliminate many experimental variables that could lead to the lack of reproducibility, such as the variable content of organic solvent or ionic strength in plasma, pH shifts, and volume shifts. Five well-known drugs were chosen to study plasma protein binding: ibuprofen, warfarin, verapamil, propranolol, and caffeine, with high, intermediate and low binding properties. Dilution of plasma with isotonic PBS or incubation with 10% CO(2) in the atmosphere was found to compensate for changes in pH during incubation. The data obtained using these pH-controlled methods correlate well with the average values of plasma protein binding found in the literature. SPME, which uses an extraction phase that dissolves or adsorbs the drug of interest and rejects proteins, overcomes several limitations of currently available techniques and is a thermodynamically sound method, since the measurements are always performed at equilibrium. Compared to other methods, SPME offers several advantages: small sample size, short analysis time, possibility to automate, and ability to directly study complex samples.
药物与血浆蛋白的结合已被证明对临床药代动力学和药效学之间的定量关系有显著影响。在许多临床情况下，测定药物总浓度并不能提供有关血浆中游离药物分数的所需信息，而游离药物分数才具有药效学作用。因此，准确测定血浆中游离药物浓度对于理解药物作用很重要。存在多种测定血浆蛋白结合程度的方法，但不同方法对同一化合物在相同浓度水平下产生的结果差异较大。本研究报道的固相微萃取（SPME）方法试图消除许多可能导致缺乏重现性的实验变量，例如血浆中有机溶剂含量或离子强度的变化、pH值变化和体积变化。选择了五种知名药物来研究血浆蛋白结合：布洛芬、华法林、维拉帕米、普萘洛尔和咖啡因，它们具有高、中、低结合特性。发现用等渗磷酸盐缓冲盐水（PBS）稀释血浆或在大气中用10%二氧化碳孵育可补偿孵育过程中的pH值变化。使用这些pH值控制方法获得的数据与文献中发现的血浆蛋白结合平均值相关性良好。SPME使用能溶解或吸附目标药物并排斥蛋白质的萃取相，克服了现有技术的几个局限性，是一种热力学合理的方法，因为测量总是在平衡状态下进行。与其他方法相比，SPME具有几个优点：样品量小、分析时间短、可实现自动化以及能够直接研究复杂样品。
