School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Pharm Res. 2010 Aug;27(8):1644-58. doi: 10.1007/s11095-010-0150-6. Epub 2010 May 7.
To investigate the permeation of two ionisable drug molecules, warfarin and verapamil, across artificial membranes. For the first time since the introduction of the parallel artificial membrane permeation assay (PAMPA) in 1998, in situ permeation-time profiles of drug molecules are studied.
The method employs a rotating-diffusion cell where the donor and acceptor compartments are separated by a lipid-impregnated artificial membrane. The permeation of the solute is investigated under well-defined hydrodynamic conditions with control over the unstirred water layer. The flux of the permeating molecule is analysed in situ using UV spectrophotometry.
In situ permeation-time profiles are obtained under hydrodynamic control and used to determine permeability coefficients. An advanced analytical transport model is derived to account for the membrane retention, two-way flux and pH gradient between the two compartments. Moreover, a numerical permeation model was developed to rationalise the time-dependent permeation profiles. The membrane permeability, intrinsic permeability and unstirred water permeability coefficients of two drug molecules are obtained from two independent methods, hydrodynamic extrapolation and pH profiling, and the results are compared.
Both warfarin and verapamil exhibit high permeability values, which is consistent with the high fraction absorbed in human. Our results demonstrate that a considerable lag-time, varying with the solute lipophilicity and stirring rate, exists in membrane permeation and leads to incorrect compound ranking if it is not treated properly. Comparison of the permeability data as a function of pH and stirring rate suggests that some transport of the ionized molecules occurs, most likely via ion-pairing.
研究两种可离子化药物分子华法林和维拉帕米穿过人工膜的渗透情况。自 1998 年平行人工膜渗透测定法（PAMPA）问世以来，首次研究了药物分子的原位渗透时间曲线。
该方法采用旋转扩散池，在供体和受体隔室之间用脂质浸渍的人工膜隔开。在控制未搅动水层的情况下，在明确定义的流体动力学条件下研究溶质的渗透情况。使用紫外分光光度法原位分析渗透分子的通量。
在流体动力学控制下获得原位渗透时间曲线，并用于确定渗透系数。推导了一个先进的分析传输模型，以解释膜保留、双向通量和两个隔室之间的 pH 梯度。此外，还开发了一个数值渗透模型来合理化时间相关的渗透曲线。通过两种独立的方法，即流体动力学外推法和 pH 分布法，从两个药物分子中获得了膜渗透性、内在渗透性和未搅动水渗透性系数，并对结果进行了比较。
华法林和维拉帕米都表现出较高的渗透性值，这与在人体中吸收的高比例相一致。我们的结果表明，在膜渗透中存在相当大的滞后时间，滞后时间随溶质的亲脂性和搅拌速度而变化，如果不加以适当处理，可能会导致化合物排序错误。比较 pH 和搅拌速度对渗透性数据的影响表明，一些离子化分子可能会发生一些传输，很可能是通过离子对形成。
