Effect of Cationic Surfactant on Transport of Model Drugs in Emulsion Systems

Excess surfactant present in emulsions can influence the rates of transport of incorporated drugs by micellar solubilization, alteration of the partitioning process and by drug-surfactant complexation. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant was selected to investigate these phenomena as it forms relatively stable mineral oil–water (O–W) emulsions and has the potential for ionic interaction. Phenylazoaniline, benzocaine, benzoic acid and phenol were chosen as model drugs for this study. The emulsion critical micelle concentration (CMC) for CTAB determined using a combination of a membrane equilibrium technique and surface-tension measurement was 10% w/v in 10% v/v% O-W emulsion systems. Ionic interaction between model drugs and surfactants and drug hydrophobicity affected their transport rates in the emulsion systems. The transport rates of the lipophilic drugs (benzocaine and phenylazoaniline) and the ionized hydrophillic drug (benzoic acid, pH 70) in the emulsion systems increased with increasing CTAB concentration up to 0–5% w/v micellar concentration and then decreased at higher concentrations. The rate of transport of phenol was not affected by the presence of micellar phase. Ionic interaction between surfactant and model drugs affected transport rates of model drugs in emulsion systems. The micellar phase was considered to affect the overall transport rates of model drugs.     

Polar Molecular Surface Properties Predict the Intestinal Absorption of Drugs in Humans

Purpose. A theoretical method has been devised for prediction of drug absorption after oral administration to humans. Methods. Twenty structurally diverse model drugs, ranging from 0.3 to 100% absorbed, were investigated. The compounds also displayed diversity in physicochemical properties such as lipophilicity, hydrogen bonding potential and molecular size. The dynamic molecular surface properties of the compounds were calculated, taking into account their three-dimensional shape and flexibility. Results. An excellent sigmoidal relationship was established between the absorbed fraction after oral administration to humans (FA) and the dynamic polar molecular surface area (PSA_d) (r² = 0.94). The relationship was stronger than those obtained for more established predictors of drug absorption. Drugs that are completely absorbed (FA > 90%) had a PSA_d 60 ² while drugs that are < 10% absorbed had a PSA_d > 140 ². Conclusions. The results indicate that PS Ad can be used to differentiate poorly absorbed drugs at an early stage of the drug discovery process.     

Predicting the Effect of Nonionic Surfactants on Dispersed Droplet Radii in Submicron Oil-in-Water Emulsions

A novel theoretical model which describes the mass mean radius of oil droplets in an oil-in-water emulsion is described. A modified form of the Langmuir adsorption isotherm is used to account for nonlinear adsorption of surfactant to an oil-water film and its effect on interfacial tension and oil droplet radius. On the basis of this model, the mass mean oil droplet radius may be related to bulk surfactant concentration for a nonionic surfactant. An analysis of the mineral oil-Triton X405-water system shows that aqueous solutions of Triton X405 against mineral oil behaved in accord with the proposed model. _m, the maximum interfacial tension lowering by Triton X405, was estimated to be 20.9 dyne/cm. A surfactant specific apparent constant (B) which relates the rate constant for adsorption to the interface to the rate constant for desorption from the interface into the aqueous bulk was estimated as 5.44E4 cm³/g. The pressure across the curved interface, P, was estimated as 1.05E6 dyne/cm². The theoretical model appears to be consistent with experimentally observed oil droplet radii and is considered to be an accurate representation of the mechanics of dispersed droplet radii under conditions of moderate load of nonionic surfactant.     

安石榴苷在MDCK细胞单层模型上的转运机制研究

摘 要 目的：采用MDCK细胞单层模型考察安石榴苷跨膜转运特性。方法: CCK8法筛选安石榴苷对MDCK细胞作用的安全浓度,Millicell ERS测量细胞单层的TEER值确定细胞单层的完整性及致密性,考察给药浓度、方向、时间、温度、维拉帕米和EDTA Na2不同条件下安石榴苷的转运情况,采用HPLC法测定安石榴苷浓度,并计算表观渗透系数( Papp ) 和外排率（ER）。结果:安石榴苷在MDCK模型上累积转运量具有时间和浓度依赖性,在100~300 μg·mL^-1浓度范围内测得的顶侧（AP）到基底侧（BL）的Papp值为（6.13±0.12）×10-7cm·s-1、（6.96±0.26）×10-7cm·s-1、（5.94±0.10）×10-7cm·s-1,未随浓度升高而增大,4℃时转运量降低,P gp 抑制药维拉帕米可以促进AP BL方向的转运,加入EDTA Na2后Papp(AP BL)显著增大。结论:安石榴苷以被动转运为主兼有主动转运参与,是P 糖蛋白（P gp）的底物受到P gp的外排作用,同时有细胞旁路转运途径。     

Dissolution of lonizable Drugs into Unbuffered Solution: A Comprehensive Model for Mass Transport and Reaction in the Rotating Disk Geometry

A model has been developed to describe the mass transport and reaction of ionizable compounds where mass transfer is caused by convection and diffusion from a rotating disk. Dissolution rates of benzoic acid, 2-naphthoic acid, and indomethacin in aqueous solutions of high ionic strength (I = 0.5 with potassium chloride) at 25°C were investigated. The model includes the effects of diffusion, convection, and simultaneous acid/base reaction at all points in the region adjacent to the dissolving solid. The solution of the transport equations is obtained numerically with an iterative algorithm which uses (a) closure of all material balances and (b) equilibria at the solid/liquid surface as constraints. The model solution yields both the flux of the dissolving acid and the concentration profile of each component. Reduced values of all reaction rate constants are used in the region adjacent to the dissolving surface to allow convergence of the computation. Although nonequilibrium concentration values are calculated, it is shown that the theoretical dissolution rate determined as the solution of the model is insensitive to the magnitude of the rate constants as their maximum useable values are approached. Comparisons of the model results with experimentally determined fluxes show close agreement and confirm that the transport mechanisms in the model formulation are consistent with the measured values. Further, the inclusion of convection allows accurate calculations without utilization of an arbitrary boundary layer thickness. Accurate dissolution rates can be determined using this technique under a wide range of conditions, except at low pH.     

The Influence of Peptide Structure on Transport Across Caco-2 Cells

The relationship between structure and permeability of peptides across epithelial cells was studied. Using confluent monolayers of Caco-2 cells as a model of the intestinal epithelium, permeability coefficients were obtained from the steady-state flux of a series of neutral and zwitterionic peptides prepared from D-phenylalanine and glycine. Although these peptides ranged in lipophilicity (log octanol/water partition coefficient) from –2.2 to +2.8, no correlation was found between the observed flux and the apparent lipophilicity. However, a strong correlation was found for the flux of the neutral series and the total number of hydrogen bonds the peptide could potentially make with water. These results suggest that a major impediment to peptide passive absorption is the energy required to break water–peptide hydrogen bonds in order for the solute to enter the cell membrane. This energy appears not to be offset by the favorable introduction of lipophilic side chains in the amino acid residues.     

药物经鼻-脑转运的离体牛嗅黏膜模型及体内外相关性

分离牛嗅黏膜，以石杉碱甲和盐酸锥双净为模型药物，用Franz扩散池，建立评价药物经鼻．脑转运的体外模型。通过测定药物透牛嗅黏膜的累积扩散率，考察药物亲脂性、浓度、pH、剂型和促透剂对其透黏膜扩散的影响，并通过测定鼻腔给药后大鼠脑脊液的药物浓度评价本模型的体内外相关性。结果表明药物透牛嗅黏膜转运以被动扩散为主，亲脂性是影响扩散的关键因素。药物透牛嗅黏膜累积扩散率与大鼠脑脊液药时曲线下面积线性相关。本研究建立的离体牛嗅黏膜模型实验手段简便，适用于经鼻脑靶向给药系统的体外评价。     

Transport of Drugs Across the Xenopus Pulmonary Membrane and Their Absorption Enhancement by Various Absorption Enhancers

Purpose. The permeability of drugs across the Xenopus pulmonary membrane and the effects of various absorption enhancers on their absorption were examined using an in vitro Ussing chamber technique. Methods. Phenol red and fluorescein isothiocyanate-labeled dextrans (FDs) with different molecular weights were chosen as water-soluble model drugs. Absorption enhancers used in this study were N-lauryl--D-maltopyranoside (LM), linoleic acid-HCO60 mixed micelle (MM), sodium glycocholate (Na-GC), sodium caprate (Na-Cap), sodium salicylate (Na-Sal) and disodium EDTA (EDTA). Results. The permeability of drugs gradually decreased with increasing their molecular weights, and the absorption of phenol red significantly increased by these absorption enhancers. Among these additives, LM, MM and Na-Cap appeared to be more effective for enhancing the permeability of drugs than the others. Furthermore, we plotted the logarithm of apparent permeability coefficient (Papp) of these drugs against the logarithm of their molecular weights. There exists a good correlation between these parameters. We measured transmembrane resistance(Rm) of Xenopus pulmonary membrane during the transport experiment to examine the membrane integrity. The average Rm value was about 700 ·crn², and this value was maintained for 3 hr. Conclusions. This method is useful for estimating the transport characteristics of drugs across the pulmonary membrane.     

The Influence of Peptide Structure on Transport Across Caco-2 Cells. II. Peptide Bond Modification Which Results in Improved Permeability

In order to study the influence of hydrogen bonding in the amide backbone of a peptide on permeability across a cell membrane, a series of tetrapeptide analogues was prepared from D-phenylalanine. The amide nitrogens in the parent oligomer were sequentially methylated to give a series containing from one to four methyl groups. The transport of these peptides was examined across confluent monolayers of Caco-2 cells as a model of the intestinal mucosa. The results of these studies showed a substantial increase in transport with each methyl group added. Only slight differences in the octanol–water partition coefficient accompanied this alkylation, suggesting that the increase in permeability is not due to lipophilicity considerations. These observations are, however, consistent with a model in which hydrogen bonding in the backbone is a principal determinant of transport. Methylation is seen to reduce the overall hydrogen bond potential of the peptide and increases flux by this mechanism. These results suggest that alkylation of the amides in the peptide chain is an effective way to improve the passive absorption potential for this class of compounds.     

Relationships in the Structure–Tissue Distribution of Basic Drugs in the Rabbit

The relationship between the tissue-to-plasma partition coefficients (K _p) and drug lipophilicity was investigated using highly lipophilic drugs with apparent partition coefficients of 150 or above in an octanol–water system at pH 7.4. Ten clinically popular basic drugs with different dissociation coefficients (pK _a) and lipophilicity were used. The K _p values were determined in nondisposing organs after the i.v. administration of individual drugs in rabbits. The free fraction in plasma and the blood-to-plasma concentration ratio were determined in vitro. Then the tissue-to-plasma ratios of nonionized and unbound drug concentrations (K _pfu) were calculated from K _pf (ratio of unbound drug). The true octanol–water partition coefficient of the nonionized drugs (P) was used to analyze the K _pf and K _pfu. In all tissues, log K _pfu was more highly correlated with log P than log K _pf.     

A Nonionic Polyethylene Oxide (PEO) Surfactant Model: Experimental and Molecular Dynamics Studies of Kolliphor EL

Polyethoxylated, nonionic surfactants are important constituents of many drug formulations, including lipid-based formulations. In an effort to better understand the behavior of formulation excipients at the molecular level, we have developed molecular dynamics (MD) models for the widely used surfactant Kolliphor EL (KOL), a triricinoleate ester of ethoxylated glycerol. In this work, we have developed models based on a single, representative molecular component modeled with 2 force field variations based on the GROMOS 53A6_DBW and 2016H66 force field parameters for polyethoxylate chains. To compare the computational models to experimental measurements, we investigated the phase behavior of KOL using nephelometry, dynamic light scattering, cross-polarized microscopy, small-angle X-ray scattering, and cryogenic transmission electron microscopy. The potential for digestion of KOL was also evaluated using an in vitro digestion experiment. We found that the size and spherical morphology of the KOL colloids at low concentrations was reproduced by the MD models as well as the growing interactions between the aggregates to from rod-like structures at high concentrations. We believe that this model reproduces the phase behavior of KOL relevant to drug absorption and that it can be used in whole formulation simulations to accelerate the formulation development.     

我院临床试验用药品管理模式的建立

目的:探讨临床试验用药品的管理模式。方法:按照《药物临床试验质量管理规范》(GCP)的规定,并结合我院实际情况制订试验用药品管理机制。结果与结论:初步建立了药物临床试验机构办公室负责试验用药品的验收、回收、督导、培训,临床专业组负责试验用药品的保管、分发和使用的试验用药品管理模式,保证试验用药品"专人、专柜、专锁"管理;同时将试验用药品的管理纳入药物临床试验质量控制体系。但建立既符合法规要求又能适应本院实际情况的、较为完善的试验用药品管理模式需要长期努力、多方协调才能达成。     

药物纳米晶的制备及其口服转运机制研究进展

现阶段提高难溶性药物口服生物利用度是药剂学研究的热点内容,其中药物纳米晶化凭借较高的载药量、较高的口服生物利用度以及易于工业化生产等优点受到广泛关注。药物纳米晶是指采用粉碎法（Top-down 法）或纳米沉淀法（Bottom-up 法）制备的除稳定剂外无其他药用载体的纳米级微粒。通常认为药物纳米晶口服给药后通过内吞作用吸收入血或通过 M 细胞介导转运至肠系膜淋巴循环,但目前尚未透彻研究药物纳米晶跨肠道上皮细胞的转运机制。综述系统介绍了纳米晶的定义、制备方法、相关的体外细胞培养模型（Caco-2,MDCK,Caco-2/HT29-MTX,Caco-2/HT29-MTX/Raji-B）以及影响纳米晶跨膜转运的因素,并通过体外细胞培养模型从分子水平上深入分析药物纳米晶跨膜转运机制。     

Predicted Permeability of the Cornea to Topical Drugs

Purpose. To develop a theoretical model to predict the passive, steady-state permeability of cornea and its component layers (epithelium, stroma, and endothelium) as a function of drug size and distribution coefficient (). The parameters of the model should represent physical properties that can be independently estimated and have physically interpretable meaning. Methods. A model was developed to predict corneal permeability using 1) a newly developed composite porous-medium approach to model transport through the transcellular and paracellular pathways across the epithelium and endothelium and 2) previous work on modeling corneal stroma using a fiber-matrix approach. Results. The model, which predicts corneal permeability for molecules having a broad range of size and lipophilicity, was validated by comparison with over 150 different experimental data points and showed agreement with a mean absolute fractional error of 2.43, which is within the confidence interval of the data. In addition to overall corneal permeability, the model permitted independent analysis of transcellular and paracellular pathways in epithelium, stroma and endothelium. This yielded strategies to enhance corneal permeability by targeting epithelial paracellular pathways for hydrophilic compounds ( < 0.1 – 1), epithelial transcellular pathways for intermediate compounds, and stromal pathways for hydrophobic compounds ( > 10 – 100). The effects of changing corneal physical properties (e.g., to mimic disease states or animals models) were also examined. Conclusions. A model based on physicochemical properties of the cornea and drug molecules can be broadly applied to predict corneal permeability and suggest strategies to enhance that permeability.     

抗微生物药招标对医院该类药品销售的影响

目的:了解抗微生物药招标对医院该类药品销售的影响。方法:根据2007年招标分类对某三级甲等医院2006年抗微生物药销售情况进行分析,并按药品规格及品种分析2007年中标的抗微生物药的降价率、使用量、日均费用、影响因子等。结果:2007年选中2006年中标的品种占2006年品种的56.48%;在2006年销售金额排序前30位中,2007年中标且入选品种11个,金额占排序前30位品种的37.73%。2007年与2006年相比,头孢孟多、头孢地嗪、帕珠沙星的影响因子较大,头孢地嗪、帕珠沙星重量影响因子排前2位。2006、2007年销售金额排序前10位的药品费用占当年总费用的比例基本一致。结论:延续使用招标药品对患者有积极意义,但降价品种使用量的降低抵消了其带来的实惠,患者平均费用没有因药品降价而减少,凸显药品招标有待完善。     

The Influence of Intestinal Mucus Components on the Diffusion of Drugs

Purpose. Mucus, a potential diffusional barrier to drug absorption, is a complex mixture of mucin and other components. The objective of this study was to investigate the composition of native pig intestinal mucus (PIM) and the influence of identified mucus components on drug diffusion. Methods. The mucus components were separated by CsCl-density gradient centrifugation and further analyzed. The self-diffusion coefficients of mannitol, metoprolol, propranolol, hydrocortisone, and testosterone, ranging in lipophilicity from logK = –3.1 to logK = 3.3, were determined, using a small scale tracer technique. The diffusion of drugs in PIM, in solutions or dispersions of individual mucus components, and in an artificial mucus model (MLPD) reconstituted from the major mucus components mucin, lipids, protein, and DNA was compared. Results. The dry weight of pig intestinal mucus contained (%, w/w); mucin (5%), lipids (37%), proteins (39%), DNA (6%), and unidentified materials. The most commonly occurring lipids were free fatty acids, cholesterol, and phospholipids while the most common protein was serum albumin. In PIM, but not in the purified pig gastric mucin (PPGM) solution, the diffusion of the lipophilic drugs metoprolol, propranolol, hydrocortisone, and testosterone was reduced compared to that of the hydrophilic drug mannitol. The diffusion of the lipophilic drugs was also significantly reduced in a dispersion of identified mucus lipids compared to that of mannitol. The diffusion in MLPD was similar to that in PIM for mannitol, propranolol, hydrocortisone, and testosterone, but somewhat lower for metoprolol. Conclusions. Lipids, rather than mucin glycoproteins, are a major component which contributes to reduced diffusion of drugs in native intestinal mucus. The results suggest that reconstituted artificial mucus models are interesting alternatives to native mucus models.     

Biodistribution Characteristics of Galactosylated Emulsions and Incorporated Probucol for Hepatocyte-Selective Targeting of Lipophilic Drugs in Mice

PURPOSE: Galactosylated emulsions containing cholesten-5-yloxy-N-(4-((1-imino-2-D-thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol) as a "homing device" were developed for hepatocyte-selective drug targeting. The targeting efficiency of galactosylated emulsions was evaluated by a distribution study in mice. METHODS: Soybean oil/EggPC/cholesterol (Chol) (weight ratio, 70:25: 5) (bare) emulsions and soybean oil/EggPC/Gal-C4-Chol (weight ratio, 70:25:5) (Gal) emulsions were prepared and labeled with [3H]cholesteryl hexadecyl ether (CHE). [14C]probucol as a model lipophilic drug was incorporated in the emulsions or EggPC/Chol/Gal-C4-Chol (Gal) liposomes. Their tissue and intrahepatic distribution were evaluated following intravenous injection in mice. RESULTS: After intravenous injection, Gal-emulsions were rapidly eliminated from the blood and accumulated in the liver, in contrast to the bare-emulsions. The liver uptake clearance of Gal-emulsions was 3.2- and 1.2-times greater than that of bare-emulsions and Gal-liposomes, respectively. The uptake ratio in liver parenchymal cells (PC) and nonparenchymal cells (NPC) of Gal-emulsions was higher than that of Gal-liposomes, being 7.4 and 3.0, suggesting that Gal-emulsions are an effective PC-selective carrier. The hepatic uptake of Gal-emulsions, but not that of bare-emulsions, was significantly inhibited by the pre-dosing of not only lactoferrin but also Gal-liposomes, suggesting asialoglycoprotein receptor-mediated endocytosis. Furthermore, [14C]probucol incorporated in Gal-emulsions was efficiently delivered to the liver compared with Gal-liposomes. CONCLUSION: Gal-emulsions have been proven to be an alternative carrier for hepatocyte-selective drug targeting.     

Role of P-Glycoprotein in Restricting Propranolol Transport in Cultured Rabbit Conjunctival Epithelial Cell Layers

Purpose. To determine the role of P-glycoprotein (P-gp) in propranololtransport in cultured rabbit conjunctival epithelial cell layers (RCEC). Methods. The localization of P-gp in the cultured RCEC as well asin the excised conjunctiva was determined by immunofluorescencetechnique. The role of P-gp in transepithelial transport and uptake ofpropranolol in conjunctival epithelial cells cultured on Transwell filterswas evaluated in the presence and absence of P-gp competing substrates, ananti-P-gp monoclonal antibody (4E3 mAb), or a metabolicinhibitor, 2, 4-dinitrophenol (2,4-DNP). Results. Immunofluorescence studies revealed positive staining in theapical membrane of cultured RCEC and in the apical surface of thesuperficial cell layers in the excised conjunctiva, but not the basolateralmembrane of cultured RCEC. Transport of propranolol showed preferencein the basolateral-to-apical direction. The net secretory flux wassaturable with a K_m of 71.5 ± 24.0 nM and a J_max of 1.45 ± 0.17pmol/cm²/hr. Cyclosporin A, progesterone, rhodamine 123, verapamil,4E3 mAb and 2,4-DNP all increased apical 50 nM propranolol uptakeby 43% to 66%. On the other hand, neither -blockers (atenolol,metoprolol, and alprenolol) nor organic cation transporter substrates(tetraethylammonium (TEA) and guanidine), affected apical 50 nMpropranolol uptake. Conclusions. The energy-dependent efflux pump P-gp appears to bepredominantly located on the apical plasma membrane of the conjunctivalepithelium. It may play an important role in restricting the conjunctivalabsorption of some lipophilic drugs.     

A Model of Human Small Intestinal Absorptive Cells. 1. Transport Barrier

The Caco-2 cell culture model of human small intestinal absorptive cells was used to investigate transepithelial transport. Transport of permeability markers such as mannitol demonstrated that Caco-2 monolayers became less permeable with increasing age in culture. Cells were routinely used for transport studies between day 18 and day 32. A transport index was determined for each compound by calculating the ratio of transport of the molecules under investigation to transport of an internal standard such as the permeability marker mannitol. Comparison of transport rates at 4 and 37°C was a simple approach for differentiating primary transport mechanisms (passive paracellular, passive transcellular, or transporter-mediated) but must be coupled with additional experimental manipulations for definitive determination of transport pathways. Compounds predicted to undergo predominantly paracellular transport (mannitol, FITC, PEG-900, and PEG-4000), transporter-mediated transcellular transport (glucose, biotin, spermidine, oralanine), or lipophilic transcellular transport (alprenolol, propranolol, clonidine, or diazepam) showed differential effects of temperature on rates of transport as well as the transport index.