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The authors present a steady-state-, particle-size-, and dose-dependent dissolution-permeation model that describes particle dissolution within the concentration boundary layer (CBL) adjacent to a semipermeable surface. It is critical to understand how particle size and dose affect the behavior of dissolving particles in the presence of a CBL adjacent to a semipermeable surface both in vivo and in vitro. Control of particle size is ubiquitous in the pharmaceutical industry; however, traditional pharmaceutical assumptions of particle dissolution typically ignore particle dissolution within the length scale of the CBL. The CBL does not physically prevent particles from traveling to the semipermeable surface (mucus, epithelial barrier, synthetic membrane, etc.), and particle dissolution can occur within the CBL thickness (delta(C)) if the particle is sufficiently small (similar to d(particle) <= delta(C)). The total flux (the time rate transport of molecules across the membrane surface per unit area) was chosen as a surrogate parameter for measuring the additional mass generated by particles dissolving within the donor CBL. Mass transfer experiments aimed to measure the total flux of drug using an ultrathin large-area membrane diffusion cell described by Sinko et al. with a silicone-based membrane (). Suspensions of ibuprofen, a model weak-acid drug, with three different particle-size distributions with average particle diameters of 6.6, 37.4, and 240 mu m at multiple doses corresponding to a range of suspension concentrations with dimensionless dose numbers of 2.94, 14.7, 147, and 588 were used to test the model. Experimentally measured total flux across the semipermeable membrane/CBL region agreed with the predictions from the proposed model, and at a range of relatively low suspension concentrations, dependent on the average particle size, there was a measurable effect on the flux due to the difference in delta(C) that formed at the membrane surface. Additionally

Fluid sampling from the gastrointestinal (GI) tract has been applied as a valuable tool to gain more insight into the fluids present in the human GI tract and to explore the dynamic interplay of drug release, dissolution, precipitation and absorption after drug product administration to healthy subjects. In the last twenty years, collaborative initiatives have led to a plethora of clinical aspiration studies that aimed to unravel the luminal drug behavior of an orally administered drug product. The obtained drug concentration-time profiles from different segments in the GI tract were a valuable source of information to optimize and/or validate predictive in vitro and in silico tools, frequently applied in the non-clinical stage of drug product development. Sampling techniques are presently not only being considered as a stand-alone technique but are also used in combination with other in vivo techniques (e.g., gastric motility recording, magnetic resonance imaging (MRI)). By doing so, various physiological variables can be mapped simultaneously and evaluated for their impact on luminal drug and formulation behavior. This comprehensive review aims to describe the history, challenges and opportunities of the aspiration technique with a specific focus on how this technique can unravel the luminal behavior of drug products inside the human GI tract by providing a summary of studies performed over the last 20 years. A section `Best practices' on how to perform the studies and how to treat the aspirated samples is described. In the conclusion, we focus on future perspectives concerning this technique.

Preclinical evaluation of modern oral dosage forms requires more advanced in vitro devices as the trend of selecting low solubility, high permeability compounds for commercial development continues. Current dissolution methodologies may not always be suitable for such compounds due to excessive fluid volume, high fluid shear rates, heterogeneity of shear rates, suboptimal fluid flow, and, ultimately, the lack of absorption ability (Gray et al. The Science of USP 1 and 2 Dissolution: Present Challenges and Future Relevance; Pharmaceutical Research, 2009; Vol. 26; pp 1289-1302). Herein, a new dissolution apparatus is introduced in combination with an ultrathin, semipermeable polymer membrane that mimics human passive absorption for lipophilic compounds. The ultrathin large-area polydimethylsiloxane (PDMS) membrane (UTLAM) absorption system is designed to mimic the dissolution and passive transcellular diffusion process representing the oral absorption pathway. A simple spin-casting method was developed to fabricate the ultrathin highly uniform membranes. To minimize membrane resistance to diffusion and maximize transport across the polymer membrane, 10-40 mu m PDMS membranes were successfully prepared. A new diffusion cell was designed and tested to support the UTLAM and incorporates a hydrofoil impeller for more desirable hydrodynamics and mixing, using ibuprofen as a model weak acidic drug. UTLAM permeability was sufficiently high that the aqueous boundary layer contributed to the overall permeability of the system. This diffusion cell system demonstrated that, when the aqueous diffusion layer contributes to the overall resistance to transport, the pH at which absorption is 50% of maximum (pH(50)(%)) shifts from the pK(a) to higher values, demonstrating why weak acid drugs can exhibit high absorption at pH's significantly greater than their pK(a). High rates of transport across the UTLAM are possible for drugs with high partition coefficients (i.e., BCS II compounds

Fluid sampling from the gastrointestinal (GI) tract has been applied as a valuable tool to gain more insight into the fluids present in the human GI tract and to explore the dynamic interplay of drug release, dissolution, precipitation and absorption after drug product administration to healthy subjects. In the last twenty years, collaborative initiatives have led to a plethora of clinical aspiration studies that aimed to unravel the luminal drug behavior of an orally administered drug product. The obtained drug concentration-time profiles from different segments in the GI tract were a valuable source of information to optimize and/or validate predictive in vitro and in silico tools, frequently applied in the non-clinical stage of drug product development. Sampling techniques are presently not only being considered as a stand-alone technique but are also used in combination with other in vivo techniques (e.g., gastric motility recording, magnetic resonance imaging (MRI)). By doing so, various physiological variables can be mapped simultaneously and evaluated for their impact on luminal drug and formulation behavior. This comprehensive review aims to describe the history, challenges and opportunities of the aspiration technique with a specific focus on how this technique can unravel the luminal behavior of drug products inside the human GI tract by providing a summary of studies performed over the last 20 years. A section `Best practices' on how to perform the studies and how to treat the aspirated samples is described. In the conclusion, we focus on future perspectives concerning this technique.

Fluid sampling from the gastrointestinal (GI) tract has been applied as a valuable tool to gain more insight into the fluids present in the human GI tract and to explore the dynamic interplay of drug release, dissolution, precipitation and absorption after drug product administration to healthy subjects. In the last twenty years, collaborative initiatives have led to a plethora of clinical aspiration studies that aimed to unravel the luminal drug behavior of an orally administered drug product. The obtained drug concentration-time profiles from different segments in the GI tract were a valuable source of information to optimize and/or validate predictive in vitro and in silico tools, frequently applied in the non-clinical stage of drug product development. Sampling techniques are presently not only being considered as a stand-alone technique but are also used in combination with other in vivo techniques (e.g., gastric motility recording, magnetic resonance imaging (MRI)). By doing so, various physiological variables can be mapped simultaneously and evaluated for their impact on luminal drug and formulation behavior. This comprehensive review aims to describe the history, challenges and opportunities of the aspiration technique with a specific focus on how this technique can unravel the luminal behavior of drug products inside the human GI tract by providing a summary of studies performed over the last 20 years. A section `Best practices' on how to perform the studies and how to treat the aspirated samples is described. In the conclusion, we focus on future perspectives concerning this technique.

Fluid sampling from the gastrointestinal (GI) tract has been applied as a valuable tool to gain more insight into the fluids present in the human GI tract and to explore the dynamic interplay of drug release, dissolution, precipitation and absorption after drug product administration to healthy subjects. In the last twenty years, collaborative initiatives have led to a plethora of clinical aspiration studies that aimed to unravel the luminal drug behavior of an orally administered drug product. The obtained drug concentration-time profiles from different segments in the GI tract were a valuable source of information to optimize and/or validate predictive in vitro and in silico tools, frequently applied in the non-clinical stage of drug product development. Sampling techniques are presently not only being considered as a stand-alone technique but are also used in combination with other in vivo techniques (e.g., gastric motility recording, magnetic resonance imaging (MRI)). By doing so, various physiological variables can be mapped simultaneously and evaluated for their impact on luminal drug and formulation behavior. This comprehensive review aims to describe the history, challenges and opportunities of the aspiration technique with a specific focus on how this technique can unravel the luminal behavior of drug products inside the human GI tract by providing a summary of studies performed over the last 20 years. A section `Best practices' on how to perform the studies and how to treat the aspirated samples is described. In the conclusion, we focus on future perspectives concerning this technique.

Fluid sampling from the gastrointestinal (GI) tract has been applied as a valuable tool to gain more insight into the fluids present in the human GI tract and to explore the dynamic interplay of drug release, dissolution, precipitation and absorption after drug product administration to healthy subjects. In the last twenty years, collaborative initiatives have led to a plethora of clinical aspiration studies that aimed to unravel the luminal drug behavior of an orally administered drug product. The obtained drug concentration-time profiles from different segments in the GI tract were a valuable source of information to optimize and/or validate predictive in vitro and in silico tools, frequently applied in the non-clinical stage of drug product development. Sampling techniques are presently not only being considered as a stand-alone technique but are also used in combination with other in vivo techniques (e.g., gastric motility recording, magnetic resonance imaging (MRI)). By doing so, various physiological variables can be mapped simultaneously and evaluated for their impact on luminal drug and formulation behavior. This comprehensive review aims to describe the history, challenges and opportunities of the aspiration technique with a specific focus on how this technique can unravel the luminal behavior of drug products inside the human GI tract by providing a summary of studies performed over the last 20 years. A section `Best practices' on how to perform the studies and how to treat the aspirated samples is described. In the conclusion, we focus on future perspectives concerning this technique.

Over the past decade, formulation predictive dissolution (fPD) testing has gained increasing attention. Another mindset is pushed forward where scientists in our field are more confident to explore the in vivo behavior of an oral drug product by performing predictive in vitro dissolution studies. Similarly, there is an increasing interest in the application of modern computational fluid dynamics (CFD) frameworks and high-performance computing platforms to study the local processes underlying absorption within the gastrointestinal (GI) tract. In that way, CFD and computing platforms both can inform future PBPK-based in silico frameworks and determine the GI-motility-driven hydrodynamic impacts that should be incorporated into in vitro dissolution methods for in vivo relevance. Current compendial dissolution methods are not always reliable to predict the in vivo behavior, especially not for biopharmaceutics classification system (BCS) class 2/4 compounds suffering from a low aqueous solubility. Developing a predictive dissolution test will be more reliable, cost-effective and less time-consuming as long as the predictive power of the test is sufficiently strong. There is a need to develop a biorelevant, predictive dissolution method that can be applied by pharmaceutical drug companies to facilitate marketing access for generic and novel drug products. In 2014, Prof. Gordon L. Amidon and his team initiated a far-ranging research program designed to integrate (1) in vivo studies in humans in order to further improve the understanding of the intraluminal processing of oral dosage forms and dissolved drug along the gastrointestinal (GI) tract, (2) advancement of in vitro methodologies that incorporates higher levels of in vivo relevance and (3) computational experiments to study the local processes underlying dissolution, transport and absorption within the intestines performed with a new unique CFD based framework. Of particular importance is revealing the physiological

The intrinsic dissolution rate and solubility of carbamazepine was measured in aqueous solutions of sodium lauryl sulfate (SLS) prepared with two different grades of purity, 95 and 99%, and 95% SLS in 0.15 M NaCl to determine the effect of surface???active impurities and electrolytes. Four significant observations resulted from this work: (1) the equilibrium coefficients calculated from the solubility experiments in the 99% SLS, 95% SLS, and 95% with 0.15 M NaCl SLS solutions were 295, 265, and 233 L/mol, respectively; (2) the dissolution rate enhancement in the 99% SLS was 10% greater than that in the 95% SLS and 95% with 0.15 M NaCl solutions, which were not significantly different; (3) the diffusion coefficients of the drug???loaded micelles estimated from the dissolution experiments were 8.4 ?? 10 ???7 cm 2 /s for the 99% SLS, 9.5 ?? 10 ???7 cm 2 /s for the 95% SLS, and 1.2 ?? 10 ???6 cm 2 /s for the 95% with 0.15 M NaCl; and (4) the critical micelle concentrations for the 99% SLS, 95% SLS, and 95% SLS with 0.15M NaCl were 6.8, 4.2, and 0.35 mM, respectively. The results of this study clearly illustrate the sensitivity of the micelle to impurities and electrolytes with regard to size and loading capacity and the effect these changes have on the solubility and dissolution rate. Therefore, when using surfactants in dissolution media for in vitro testing of dosage forms, consideration must be given to the level of impurities present so that the results are consistent and reliable. Intrinsic dissolution rate, surface tension, or solubility measurements may be useful, convenient methods for identifying changes in the surfactant due to either degradation or lot???to???lot variability.

The drug intestinal permeability (P-eff) measure has been widely used as one of the main factors governing both the rate and/or extent of drug absorption (F-abs) in humans following oral administration. In this communication we emphasize the complexity behind and the care that must be taken with this in vivo Puff measurement. Intestinal permeability, considering the whole of the human intestine, is more complex than generally recognized, and this can lead to misjudgment regarding F-abs and P-err in various settings, e.g. drug discovery, formulation design, drug development and regulation. Setting the adequate standard for the low/high permeability class boundary, the different experimental methods for the permeability measurement, and segmental-dependent permeability throughout the human intestine due to different mechanisms are some of the main points that are discussed. Overall, the use of jejunal P-eff as a surrogate for extent of absorption is sound and scientifically justified; a compound with high jejunal P-eff will have high F-abs, eliminating the risk for misclassification as a BCS class I drug. Much more care should be taken, however, when jejunal P-eff does not support a high-permeability classification; a thorough examination may reveal high-permeability after all, attributable to e.g. segmental-dependent permeability due to degree of ionization or transporter expression. In this situation, the use of multiple permeability experimental methods, including the use of metabolism, which except for huminal degradation requires absorption, is prudent and encouraged.

The FDA classifies a drug substance as high-permeability when the fraction of dose absorbed (F-abs) in humans is 90% or higher. This direct correlation between human permeability and Fab, has been recently controversial, since the beta-blocker sotalol showed high F-abs (90%) and low Caco-2 permeability. The purpose of this study was to investigate the scientific basis for this disparity between permeability and F-abs. The effective permeabilities (P-eff) of sotalol and metoprolol, a FDA standard for the low/high P-off class boundary, were investigated in the rat perfusion model, in three different intestinal segments with pHs corresponding to the physiological pH in each region: (1) proximal jejunum, pH 6.5; (2) mid small intestine, pH 7.0; and (3) distal ileum, pH 7.5. Both metoprolol and sotalol showed pH-dependent permeability, with higher P-eff at higher pH. At any given pH, sotalol showed lower permeability than metoprolol; however, the permeability of sotalol determined at pH 7.5 exceeded/matched metoprolol's at pH 6.5 and 7.0, respectively. Physicochemical analysis based on ionization, pK(a) and partitioning of these drugs predicted the same trend and clarified the mechanism behind these observed results. Experimental octanol buffer partitioning experiments confirmed the theoretical curves. An oral dose of metoprolol has been reported to be completely absorbed in the upper small intestine; it follows, hence, that metoprolol's P-eff, value at pH 7.5 is not likely physiologically relevant for an immediate release dosage form, and the permeability at pH 6.5 represents the actual relevant value for the low/high permeability class boundary. Although sotalol's permeability is low at pH 6,5 and 7.0, at pH 7.5 it exceeds/matches the threshold of metoprolol at pH 6.5 and 7.0, most likely responsible for its high Faros, In conclusion, we have shown that, in fact, there is no discrepancy between P-eff and F-abs, in sotalol's absorption; the data emphasize that, if a com

The purpose of this study was to compare the expression profiles of drug-metabolizing enzymes in the intestine of mouse, rat and human. Total RNA was isolated from the duodenum and the mRNA expression was measured using Affymetrix GeneChip oligonucleotide arrays. Detected genes from the intestine of mouse, rat and human were ca. 60% of 22690 sequences, 40% of 8739 and 47% of 12559, respectively. Total genes of metabolizing enzymes subjected in this study were 95, 33 and 68 genes in mouse, rat and human, respectively. Of phase I enzymes, the mouse exhibited abundant gene expressions for Cyp3a25, Cyp4v3, Cyp2d26, followed by Cyp2b20, Cyp2c65 and Cyp4f14, whereas, the rat showed higher expression profiles of Cyp3a9, Cyp2b19, Cyp4f1, Cyp17a1, Cyp2d18, Cyp27a1 and Cyp4f6. However, the highly expressed P450 enzymes were CYP3A4, CYP3A5, CYP4F3, CYP2C18, CYP2C9, CYP2D6, CYP3A7, CYP11B1 and CYP2B6 in the human. For phase II enzymes, glucuronosyltransferase Ugt1a6, glutathione S-transferases Gstp1, Gstm3 and Gsta2, sulfotransferase Sult1b1 and acyltransferase Dgat1 were highly expressed in the mouse. The rat revealed predominant expression of glucuronosyltransferases Ugt1a1 and Ugt1a7, sulfotransferase Sult1b1, acetyltransferase Dlat and acyltransferase Dgat1. On the other hand, in human, glucuronosyltransferases UGT2B15 and UGT2B17, glutathione S-transferases MGST3, GSTP1, GSTA2 and GSTM4, sulfotransferases ST1A3 and SULT1A2, acetyltransferases SAT1 and CRAT, and acyltransferase AGPAT2 were dominantly detected. Therefore, current data indicated substantial interspecies differences in the pattern of intestinal gene expression both for P450 enzymes and phase II drug-metabolizing enzymes. This genomic database is expected to improve our understanding of interspecies variations in estimating intestinal prehepatic clearance of oral drugs. Copyright © 2009 John Wiley & Sons, Ltd.

The workshop "Bioequivalence, Biopharmaceutics Classification System, and Beyond" was held May 21-23, 2007 in North Bethesda, MD, USA. This workshop provided an opportunity for pharmaceutical scientists to discuss the FDA guidance on the Biopharmaceutics Classification System (BCS), bioequivalence of oral products, and related FDA initiatives such as the FDA Critical Path Initiative. The objective of this Summary Workshop Report is to document the main points from this workshop. Key highlights of the workshop were (a) the described granting of over a dozen BCS-based biowaivers by the FDA for Class I drugs whose formulations exhibit rapid dissolution, (b) continued scientific support for biowaivers for Class III compounds whose formulations exhibit very rapid dissolution, (c) scientific support for a number of permeability methodologies to assess BCS permeability class, (d) utilization of BCS in pharmaceutical research and development, and (e) scientific progress in in vitro dissolution methods to predict dosage form performance.

We recommend that regulatory agencies add the extent of drug metabolism (i.e., >or=90% metabolized) as an alternate method in defining Class 1 marketed drugs suitable for a waiver of in vivo studies of bioequivalence. That is, >or=90% metabolized is an additional methodology that may be substituted for >or=90% absorbed. We propose that the following criteria be used to define>or=90% metabolized for marketed drugs: Following a single oral dose to humans, administered at the highest dose strength, mass balance of the Phase 1 oxidative and Phase 2 conjugative drug metabolites in the urine and feces, measured either as unlabeled, radioactive labeled or nonradioactive labeled substances, account for >or=90% of the drug dosed. This is the strictest definition for a waiver based on metabolism. For an orally administered drug to be >or=90% metabolized by Phase 1 oxidative and Phase 2 conjugative processes, it is obvious that the drug must be absorbed. This proposal, which strictly conforms to the present>or=90% criteria, is a suggested modification to facilitate a number of marketed drugs being appropriately assigned to Class 1.

Purpose. To study the correlation of intestinal absorption for drugs with various absorption routes between human and rat, and to explore the underlying molecular mechanisms for the similarity in drug intestinal absorption and the differences in oral bioavailability between human and rat. Materials and Methods. The intestinal permeabilities of 14 drugs and three drug-like compounds with different absorption mechanisms in rat and human jejunum were determined by in situ intestinal perfusion. A total of 48 drugs were selected for oral bioavailability comparison. Expression profiles of transporters and metabolizing enzymes in both rat and human intestines (duodenum and colon) were measured using GeneChip analysis. Results. No correlation (r(2) = 0.29) was found in oral drug bioavailability between rat and human, while a correlation (r(2) = 0.8) was observed for drug intestinal permeability with both carrier-mediated absorption and passive diffusion mechanisms between human and rat small intestine. Moderate correlation (with r(2) > 0.56) was also found for the expression levels of transporters in the duodenum of human and rat, which provides the molecular mechanisms for the similarity and correlation of drug absorption between two species. In contrast, no correlation was found for the expressions of metabolizing enzymes between rat and human intestine, which indicates the difference in drug metabolism and oral bioavailability in two species. Detailed analysis indicates that many transporters (such as PepT1, SGLT-1, GLUT5, MRP2, NT2, and high affinity glutamate transporter) share similar expression levels in both human and rat with regional dependent expression patterns, which have high expression in the small intestine and low expression in the colon. However, discrepancy was also observed for several other transporters (such as MDR1, MRP3, GLUT1, and GLUT3) in both the duodenum and colon of human and rat. In addition, the expressions of metabolizing enzymes (CYP3A4

The primary objective of this study was to define the pH conditions under which supplemental pancreatic enzyme preparations must function in the upper gastrointestinal tract. The hypothesis was that normal or greater gastric acid output in patients with cystic fibrosis (CF), combined with low pancreatic bicarbonate output, results in an acidic duodenal pH, compromising both dosage-form performance and enzyme activity. Gastrointestinal pH profiles were obtained in 10 CF and 10 healthy volunteers under fasting and postprandial conditions. A radiotelemetric monitoring method, the Heidelberg capsule, was used to continuously monitor pH. Postprandial duodenal pH was lower in CF than in healthy subjects, especially in the first postprandial hour (mean time greater than pH 6 was 5 min in CF, 11 min in healthy subjects, P <0.05). Based on the dissolution pH profiles of current enteric-coated pancreatic enzyme products, the duodenal postprandial pH in CF subjects may be too acidic to permit rapid dissolution of current enteric-coated dosage forms. However, the pH was above 4 more than 90% of the time on the average, suggesting that irreversible lipase inactivation in the duodenum is not likely to be a significant limitation to enzyme efficacy. Overall results suggest that slow dissolution of pH-sensitive coatings, rather than enzyme inactivation, may contribute to the failure of enteric-coated enzyme supplements to normalize fat absorption.

Poly(hydroxyethyl methacrylate???co???methacrylie acid) hydrogels can swell extensively in a high-pH medium where the carboxyl groups are ionized. The swelling equilibrium is a strong function of the methacrylic acid composition of the polymer and pH of the medium. The nonionized gel structure was found to be rather insensitive to the amount of cross-linker, tetraethylene glycol dimethacrylate (TEGDMA), incorporated, within the range of 0.5 to 3%. This result is supportive of the existence of secondary interactions that shield the effect of covalent cross-links. Phenylpropanolamine (PPA) was used as a probe solute to study the diffusion characteristics of the poly (HEMA???co???MA) gels. Its diffusion coefficient in the swollen matrices of different methacrylic acid compositions at various pH's was measured via a desorption method. It is evident that these diffusion coefficients follow Yasuda's free volume theory, which expresses an exponential relationship between the solute diffusivity in a swollen polymer membrane and the reciprocal of the membrane hydration. Although interactions exist between PPA and the hydrogel matrix, these interactions are not significant enough to perturb the free volume relationship established. This observation can be explained by the high ionic strength of the system.

Intestinal permeabilities of five dipeptidyl derivatives of L-??-methyldopa (I) were studied by an in situ intestinal perfusion method. The dipeptides displayed a significant increase in their permeabilities compared to L-??-methyldopa. The increases ranged from 4 to 20 times. These results suggest that the peptide transport system is less structurally specific than the amino acid transport systems and can be used as an absorption pathway for peptide analogues. The kinetic advantage demonstrated by the dipeptide, L-??-methyldopa-L-phenylalanine, over the amino acid analogue, L-??-methyldopa, suggests that the peptide carrier would be a possible route for improving the intestinal absorption of pharmacologically active amino acid analogues. Furthermore, the preliminary results of in vitro hydrolysis studies of selected dipeptidyl derivatives indicate that the peptide carrier system could be used as a base for a prodrug strategy.

Based on a simple tube model for drug absorption, the key parameters controlling drug absorption are shown to be the dimensionless effective permeability, P eff *, and the Graetz number, Gz, when metabolism or solubility/dissolution is not rate controlling. Estimating the Graetz number in humans and assuming that P aq * is not rate controlling gives the following equation for fraction dose absorbed: F = 1??? e???2 P*w . The correlation between fraction dose absorbed in humans and P w * determined from steady-state perfused rat intestinal segments gives an excellent correlation. It is of particular significance that the correlation includes drugs that are absorbed by passive and carrier-mediated processes. This indicates that P w * is one of the key variables controlling oral drug absorption and that the correlation may be useful for estimating oral drug absorption in humans regardless of the mechanism of absorption.

The single-pass intestinal perfusion technique has been used extensively to estimate the wall permeability in rats. The unbiased membrane parameters can be obtained only when the aqueous resistance is properly accounted for. This aqueous resistance was calculated numerically from a convective diffusive mass transfer model, including both passive and carrier-mediated transport at the intestinal wall. The aqueous diffusion layer resistance was shown to be best described by a function of the form, where G z, P * m P * c K m and C o are, respectively, Graetz number, passive permeability, carrier-mediated permeability, Michaelis constant, and the drug concentration entering the tube. Asterisked are dimensionless quantities obtained by multiplying the permeability constants with R/D, where R and D being radius and drug diffusivity, respectively. A, B, C, D and E were obtained by a least-squares nonlinear regression method, giving values of 1.05, 1.74, 1.27, 0.0659, and 0.377, respectively, over the range of 0.001??? G z??? 0.5, 0.01??? P * m??? 10, 0.01??? P * c??? 10, and 0.01??? K m / C o??? 100. This aqueous resistance was found to converge to those calculated from Levich's boundary layer solution in low Graetz range, indicating the correct theoretical limit. Using an iteration method, the equation was shown to be useful in extracting the intrinsic membrane permeability from the experimental data.

Purpose . To compare gene expression profiles and drug permeability differences in Caco-2 cell culture and human duodenum.

Purpose. To synthesize fluorescent analogues of hPept1 substrates, FITC-Val-OCH 3, Lys-FITC-OH, and Lys-FITC-OCH 3, and to characterize their hPept1 transporter-mediated uptake.

We investigated the effects of the nonionic surfactant, n -decylmethyl sulfoxide (NDMS), pH, and inhibitors on the metabolism and the permeation of amino acids, dipeptides, and the pentapeptide enkephalin, through hairless mouse skin. An HPLC gradient method was developed to identify the possible peptide and amino acid metabolites of leucine-enkephalin. NDMS increased the permeability of all amino acids and peptides tested. At neural pH, the enzyme activity within the skin was such that no flux of leucine-enkephalin (YGGFL) was observed and the donor cell concentration of YGGFL decreased rapidly. The major cleavage occurred at the Tyr-Gly bond. At pH 5.0 the metabolic activity was reduced significantly and a substantial flux of YGGFL was observed. Enzymatically stable YGGFL analogues, Tyr-D-Ala-Gly-Phe-Leu (YDAGFL) and its amide, exhibited significant fluxes even at neutral pH in the presence of NDMS, but with substantial metabolism. YDAGFL amide was more stable to metabolism than YDAGFL. The rates of metabolism of the peptides in the skin homogenates were in the order: FL.>>YGGFL> GFL> GGFL>> YG, YGG>> YDAGFL amide. In the skin homogenates puromycin and amastatin showed the highest inhibitory effects, while FL and GFL were only slightly active. However, in the skin diffusion experiments, FL allowed the highest amount of intact parent compound to permeate, making it the most potent inhibitor. These results show that the complex proteolytic enzyme activities occurring during skin permeation are different from those in skin homogenates and that a combination of enhancer, pH adjustment, and inhibitors can increase the transdermal delivery of peptides.

Purpose . To determine the human jejunal permeability of cimetidine and ranitidine using a regional jejunal perfusion approach, and to integrate such determinations with previous efforts to establish a baseline correlation between permeability and fraction dose absorbed in humans for soluble drugs.

The oral absorption of five cephalosporin antibiotics, cefaclor, cefadroxil, cefatrizine, cephalexin, and cephradine, has been studied using a single-pass intestinal perfusion technique in rats. Intrinsic membrane absorption parameters,???unbiased??? by the presence of an aqueous permeability (diffusion or stagnant layer), have been calculated utilizing a boundary layer mathematical model. The resultant intrinsic membrane absorption parameters are consistent with a significant carrier-mediated, Michaelis-Menten-type kinetic mechanism and a small passive component in the jejunum. Cefaclor colon permeability is low and does not exhibit concentration dependent behavior. The measured carrier parameters (??SD) for the jejunal perfusions are as follows: cefaclor, J max * = 21.3 (??4.0), K m = 16.1 (??3.6), P m * = 0, and P c * = 1.32 (??0.07); cefadroxil, J max * = 8.4 (??0.8), K m = 5.9 (??0.8), P m * = 0, and P c * = 1.43 (??0.10); cephalexin, J max * = 9.1 (??1.2), K m = 7.2 (??1.2), P m * = 0, and P c * = 1.30 (??0.10); cefatrizine, J max * = 0.73 (??0.19), K m = 0.58 (??0.17), P m * = 0.17 (??0.03), and P c * = 1.25 (??0.10); and cephradine, J max * = 1.57 (??0.84), K m = 1.48 (??0.75), P m * = 0.25 (??0.07), and P c * = 1.06 (??0.08). The colon absorption parameter for cefaclor is P m * = 0.36 (??0.06, where J max * (m M) is the maximal flux, K m (m M) is the Michaelis constant, P m * is the passive membrane permeability, and P c *is the carrier permeability. Aminocephalosporin perfusion results indicate that jejunal absorption in the rat occurs by a nonpassive process, with some of the compounds possessing a small but statistically significant passive component, while the colon permeability is low and follows a simple passive absorption mechanism.

Polyethylene glycols (PEGs) 600,1000, and 2000 were used to study the molecular weight permeability dependence in the rat nasal and gastrointestinal mucosa. Absorption of the PEGs was measured by following their urinary excretion over a 6-hr collection period. HPLC methods were used to separate and quantitate the individual oligomeric species present in the PEG samples. The permeabilities of both the gastrointestinal and the nasal mucosae exhibited similar molecular weight dependencies. The steepest absorption dependence for both mucosae occurs with the oligomers of PEG 600, where the extent of absorption decreases from approximately 60% to near 30% over a molecular weight range of less than 300 daltons. Differences in the absorption characteristics between the two sites appear in the molecular weight range spanned by PEG 1000. For these oligomers, the mean absorption from the nasal cavity is approximately 14%, while that from the gastrointestinal tract is only 9%. For PEG 2000, mean absorption decreases to 4% following intranasal application and below 2% following gastrointestinal administration. Within the PEG 1000 and 2000 samples, however, very little molecular weight dependency is seen among the oligomers. In the range studied, a distinct molecular weight cutoff was not apparent at either site.

The reduced 3-suffix solubility equation (R3SSE) is applied to the characterization of solubility in the ethanol???water system. The data needed are the solubility of the compound in each of the pure solvents and at one ethanol???water composition. This composition has been estimated from solubility data to be 0.56 volume fraction of ethanol. The solubility obtained at this volume fraction is used to estimate the ternary solute???solvent interaction constant, C 2 . The R3SSE, with the C 2 thus obtained, predicts the mixed solvent solubilities of the compounds tested, as accurately as that obtained from several volume fractions. The superiority of the R3SSE over two related equations???a simple second-degree polynomial equation and a simplified form of the R3SSE which neglects contributions to solubility from the solvent mixture???is also demonstrated for a number of solutes.

Purpose. The purpose of this work was to determine the jejunal permeability of cyclosporin A (CsA) in humans and whether formulation variables modulate the effects of P-glycoprotein (P-gp) on the permeability of CsA in Caco-2 cells.

The pharmacokinetics of ibuprofen are complicated by the unidirectional metabolic inversion of the (???)-R- to (+)-S-enantiomer. Chiral inversion is of therapeutic significance since the drug???s pharmacologic activity has been shown to depend upon the (+)-S-isomer. As a result, the present study was undertaken to determine if chiral inversion occurs systemically and to elucidate further the kinetics of the inversion process. Experiments were performed in the beagle dog after intravenous bolus injections of ibuprofen enantiomers separately [100 mg (???)-R, n = 4; 100 mg (+)-S, n = 4] and as admixtures of varying proportions [100 mg (???)-R + 100 mg (+)-S, n = 4; 100 mg (???)-R + 200 mg (+)-S, n = 2]. Plasma samples of (???)-R-and (+)-S-enantiomers were measured by a stereospecific HPLC assay after all drug administrations. Based on the area under the plasma concentration???time curves for (+)-S after administration of each enantiomer alone, chiral inversion was 70 to 75%. A progressive reduction in total plasma clearance of (???)-R-ibuprofen is also observed as increasing amounts of (+)-S-enantiomer are added to the system. The results demonstrate that chiral inversion occurs to a significant extent in the systemic circulation in dog and that R-to-S inversion of ibuprofen may be inhibited by its ((+)-S-enantiomer.

Purpose . To study the uptake of biodegradable microparticles in Caco-2 cells.

Leu-enkephalin (YGGFL) and several analogues were chosen as model peptides for the study of peptide absorption and hydrolysis in the rat jejunum. An HPLC assay was adapted to detect YGGFL or the analogues and metabolites. Peptide hydrolysis was studied in the rat jejunum using a single-pass perfusion method. Extensive hydrolysis of YGGFL was observed in the rat jejunum and approaches to reduce its metabolism were studied. The brush border enzymes are a major site of enkephalin hydrolysis. Lumenal peptidases were secondary to the brush border enzymes in hydrolyzing the enkephalins in this system. In the in situ perfusion system, YGGFL is hydrolyzed primarily to Tyr and GGFL by the brush border aminopeptidase and to YGG and FL by brush border endopeptidase. Lowering the jejunal pH below 5.0 significantly reduces aminopeptidase activity and, to a lesser extent, endopeptidase activity. An aminopeptidase inhibitor, amastatin, produced more pronounced inhibitory effects at higher pH and the endopeptidase inhibitors, tripeptides YGG and GGF, are effective even below pH 5.0. Coperfusion of YGGFL with a combination of aminopeptidase and endopeptidase inhibitors, e.g., amastatin and YGG, is more effective in inhibiting hydrolysis since both metabolic pathways are inhibited. Leu-D(Ala) 2 -enkephalin, while showing enhanced stability against aminopeptidase hydrolysis, is hydrolyzed at the Gly???Phe bond by the endopeptidase. Its hydrolysis is not affected by pH changes or amastatin but is decreased by YGG. The YGGFL wall permeability was estimated and is not a limiting factor for oral absorption.

A series of polyethylene glycols (PEGs) ranging in molecular weight from near 600 to over 2000 daltons was used to study the effects of three absorption enhancers (sodium glycocholate, sodium lauryl sulfate, and polyoxyethylene 9 lauryl ether) on the molecular weight permeability profile of the nasal mucosa of the rat. Molecular weight???permeability properties were studied both by following changes in the excretion of the polyethylene glycols as a function of their molecular size and by examining the nasal mucosa for morphologic changes following exposure to the PEG/enhancer mixtures. Each absorption enhancer was found to affect the mucosa and its permeability in a unique manner. At a 1% concentration, sodium glycocholate only slightly affects tissue morphology and does not significantly alter the molecular weight permeability profile of the mucosa. In contrast, 1% sodium lauryl sulfate causes severe alteration of the mucosa and also greatly increases the absorption of both the PEG 600 and the PEG 2000 oligomers. Polyoxyethylene 9 lauryl ether was found to exert its action in a concentration-dependent manner. At a concentration of 0.1%, few changes were seen in either mucosal integrity or permeability. At a 1% concentration, however, a significant alteration in the structure of the mucosal tissues as well as a profound increase in the permeability of the mucosa to the PEGs was observed. Correlation of mucosal integrity with the effectiveness of an enhancer indicates that some of these compounds appear to be acting by altering the structure of the mucosa. Others, which appear to exert a less damaging effect on the mucosal cells themselves, achieve their greatest absorption enhancement when changes in cell-to-cell adhesion in the mucosa are observed. These results indicate that the paracellular routes may play an important role in large molecule absorption through the nasal mucosa.

The requirement for a free??-amino group for the intestinal peptide carrier-mediated transport was investigated. A series of dipeptide analogues without the N-terminal??-amino group [including phenyl-propionylproline, phenylacetylproline, N -benzoylproline, phenylacetyl-??-methyldopa, and hippuric acid (N -benzoylglycine)] were studied in the perfused rat intestinal segment. The absorption of phenylpropionylproline, phenylacetyl-??-methyldopa, and N -benzoylproline was concentration dependent. The transport parameters (mean?? SD) of phenylpropionylproline and N -benzoylproline were as follows: J max*, 0.037 (??0.019) m M ; K m, 0.045 (??0.027) m M ; P c*, 0.830 (??0.130); and P m*, 0.673?? 0.049; and J max*, 1.34 (??0.24) m M ; K m, 1.31 (??0.30) m M ; P c*, 1.02 (??0.11); and P m* 0; respectively. The intestinal permeabilities of phenylpropionylproline, phenylacetylproline, N -benzoylproline, and hippuric acid (N -benzoylglycine) were significantly reduced by dipeptides and ceph-radine. These results strongly suggest that these dipeptide analogues, without an??-amino group, are transported by the peptide carrier and provide more direct evidence that a free??-amino group is not absolutely essential for the mucosal-cell peptide carrier-mediated transport.

Purpose . To synthesize amino acid ester prodrugs of floxuridine (FUdR) and to investigate the effects of structure, stereochemistry, and site of esterification of promoiety on the rates of hydrolysis of these prodrugs in Caco-2 cell homogenates.

Purpose . Adenoviral (Ad) vectors have been used as efficient tools for gene therapy in various tissues, whereas in some differentiated epithelium transduction efficiency is almost abolished.

The influence of formulation variables on the rheology of polyanionic formulations and the relationships between viscoelastic properties and mucociliary transport rate were investigated. Polymeric samples were oscillated from 0.001 to 5 Hz using either a "cone and plate??? or a "coaxial cylinder??? measuring system. The mucociliary transport rates of polymeric samples were determined and compared movement of charcoal powder on the frog palate. For the linear polymeric solutions, sodium carboxymethylcellulose and sodium alginate, the elastic modulus (G???) increased with increasing amplitudes during frequency scan. However, the G??? or viscous modulus (G???) of partially cross-linked polyacrylic acid (cPAA) samples did not change significantly under oscillation. Both G??? and G??? of cPAA samples were significantly influenced by the amount of salt present in the formulation. The rheology of 2% (w/w) cPAA in 90:10 (w/w) propylene glycol:alcohol changed from a viscous fluid to a coarse suspension after neutralization. The pH increased gradually when the nonaqueous formulation reacted with water and the maximum dynamic moduli were obtained after incorporating 20% (w/w) water in the formulation. A negative correlation was found between the G??? of linear polyanionic samples and the relative transport rate. However, the lowest mucociliary transport rate was observed when the loss tangent (G???/ G???) was around 0.4???0.5.

Purpose . This study characterized the cellular uptake mechanism and hydrolysis of the amino acid ester prodrugs of nucleoside antiviral drugs in the transiently transfected Caco-2 cells overexpressing a human intestinal peptide transporter, hPEPTl (Caco-2/hPEPTl cells).

Purpose . In general, the intestinal epithelium is quite refractory to viral and non-viral methods of gene transfer. In this report, various cyclodextrin formulations were tested for their ability to enhance adenoviral transduction efficiency in two models of the intestinal epithelium: differentiated Caco-2 cells and rat jejunum.

Purpose . The objective of this study was to evaluate drug marker absorption in relation to the gastric emptying (GE) of 0.7 mm and 3.6 mm enteric coated pellets as a function of viscosity and the underlying gastric motility.

Purpose . The objective of this research was to investigate the substrate specificity of large neutral amino acid carrier (LNAA) and di/tripeptide (hPEPTl) transporters with respect to PD 158473, an NMDA antagonist.

This study reports the results of the combined effect of pH and surfactant on the dissolution of piroxicam (PX), an ionizable water-insoluble drug in physiological pH. The intrinsic dissolution rate ( J total ) of PX was measured in the pH range from 4.0 to 7.8 with 0%, 0.5%, and 2.0% sodium lauryl sulfate (SLS) using the rotating disk apparatus. Solubility ( c total ) was also measured in the same pH and SLS concentration ranges. A simple additive model including an ionization (PX ↔ H + + PX − ) and two micellar solubilization equilibria (PX + micelle ↔ [PX] micelle , PX − + micelle ↔ [PX − ] micelle ) were considered in the convective diffusion reaction model. J total and c total of PX increased with increasing pH and SLS concentration in an approximately additive manner. Nonlinear regression analysis showed that observed experimental data were well described with the proposed model ( r 2 = 0.86, P < 0.001 for J total and r 2 = 0.98, P < 0.001 for c total ). The p K a value of 5.63 ± 0.02 estimated from c total agreed well with the reported value. The micellar solubilization equilibrium coefficient for the unionized drug was estimated to be 348 ± 77 L/mol, while the value for the ionized drug was nearly equal to zero. The diffusion coefficients of the species PX, PX − , and [PX] micelle were estimated from the experimental results as (0.93 ± 0.35) × 10 −5 , (1.4 ± 0.30) × 10 −5 , and (0.59 ± 0.21) × 10 −5 cm 2 /s, respectively. The total flux enhancement is less than the total solubility enhancement due to the smaller diffusion coefficients of the micellar species. This model may be useful in predicting the dissolution of an ionizable water insoluble drug as a function of pH and surfactant and for establishing in vitro - in vivo correlations, IVIVC, for maintaining bioequivalence of drug products. © 2000 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 268-274, 2000

The viscoelastic propertied of model polymer, hydroxypropylmethylcellulose (HPMC), in ternary solvent mixtures and the variation of viscoelastic properties under dilution with water were investigated. HPMC was dispersed in mixtures of glycerol formal (GF) or ethyl alcohol, propylene glycol (PG), and water. Each polymeric sample was oscillated at different frequencies with fixed stress amplitude and the changes in elastic modulus, viscous modulus, and apparent viscosity were measured at 30[deg]C. The moisture absorption rate of HPMC in PG:GF solvent mixtures in a 94% relative humidified environment was also studied. A linear relationship between the elastic modulus or viscous modulus and polymer concentration was observed for the HPMC samples. The relative mucociliary transport rate tested on the non-depleted frog palate model revealed a curvilinear correlation with the loss tangent (a ratio of the viscous modulus to the elastic modulus) of the polymeric solution. Using GF as a solvent for HPMC resulted in a formation of a rigid gel with the highest elastic modulus and viscous modulus among solvents selected. A higher affinity for water was found for HPMC in the PG:GF 90:10 mixture compared with HPMC in the PG:GF 70:30 mixture. However, the elastic modulus and viscous modulus were much higher for HPMC in the PG:GF 70:30 mixture.