Effects of Membrane Type and Liquid/Liquid Phase Boundary onIn VitroRelease of Ketoprofen from Gel Formulations

Comparison Between Franz Diffusion Cell and a novel Micro-physiological System for In Vitro Penetration Assay Using Different Skin Models

In vitro diffusive models are an important tool to screen the penetration ability of active ingredients in various formulations. A reliable assessment of skin penetration enhancing properties, mechanism of action of carrier systems, and an estimation of a bioavailability are essential for transdermal delivery. Given the importance of testing the penetration kinetics of different compounds across the skin barrier, several in vitro models have been developedThe aim of this study was to compare the Franz Diffusion Cell (FDC) with a novel fluid-dynamic platform (MIVO) by evaluating penetration ability of caffeine, a widely used reference substance, and LIP1, a testing molecule having the same molecular weight but a different lipophilicity in the two diffusion chamber systems. A 0.7% caffeine or LIP1 formulation in either water or propylene glycol (PG) containing oleic acid (OA) was topically applied on the Strat-M® membrane or pig ear skin, according to the infinite-dose experimental condition (780 ul/cm²). The profile of the penetration kinetics was determined by quantify the amount of molecule absorbed at different time-points (1, 2, 4, 6, 8 hours), by means of HPLC analysis. Both diffusive systems show a similar trend for caffeine and LIP1 penetration kinetics. The Strat-M® skin model shows a lower barrier function than the pig skin biopsies, whereby the PGOA vehicle exhibits a higher penetration, enhancing the effect for both diffusive chambers and skin surrogates. Most interestingly, MIVO diffusive system better predicts the lipophilic molecules (i.e. LIP1) permeation through highly physiological fluid flows resembled below the skin models.

Ethosomes and Transethosomes as Cutaneous Delivery Systems for Quercetin: A Preliminary Study on Melanoma Cells

The present study is aimed to design ethosomes and transethosomes for topical administration of quercetin. To overcome quercetin low bioavailability, scarce solubility and poor permeability that hamper its pharmaceutical use, the drug was loaded in ethosomes and transethosomes based on different concentrations of phosphatidylcholine. Vesicle morphology was studied by cryogenic transmission electron microscopy, while size distribution and quercetin entrapment capacity were evaluated up to 3 months, respectively, by photon correlation spectroscopy and high-performance liquid chromatography. The antioxidant property was studied by photochemiluminescence test. Quercetin release and permeation was investigated in vitro, using Franz cells associated to different membranes. In vitro assays were conducted on human keratinocytes and melanoma cells to study the behavior of quercetin-loaded nano-vesicular forms with respect to cell migration and proliferation. The results evidenced that both phosphatidylcholine concentration and quercetin affected the vesicle size. Quercetin entrapment capacity, antioxidant activity and size stability were controlled using transethosomes produced by the highest amount of phosphatidylcholine. In vitro permeation studies revealed an enhancement of quercetin permeation in the case of transethosomes with respect to ethosomes. Notably, scratch wound and migration assays suggested the potential of quercetin loaded-transethosomes as adjuvant strategy for skin conditions.

Impact of Membranes on In Vitro Release Assessment: a Case Study Using Dexamethasone

In vitro release studies are commonly used to assess the product performance of topical dosage forms. In such studies, the mass transport of drugs through synthetic membranes into a receiving chamber filled with a release medium is measured. The release medium is also passed through filtration membranes prior to chromatographic analysis. There are no official guidelines directing membrane selection for in vitro release studies or for filtration. Considering the diversity in membrane materials and their physical properties, the aim of this study was to investigate membrane-drug binding and the effect of various membranes on the release performance of a model drug dexamethasone (DEX) using USP dissolution apparatus IV. Seven membranes of different pore sizes (0.45 and 1.2 μm) and materials (cellulose acetate, polyethersulfone, and nylon) were assessed. Two different methods, syringe filter and 24-h incubation, were used for the determination of membrane-drug binding effects at low drug concentrations and saturated concentration conditions. Cellulose acetate and nylon membranes showed significant drug binding after 24-h incubations at both drug concentrations. DEX diffusion through membranes was significantly slowed down in all the tested membranes when compared with DEX solution without membranes. The extent of the retardation varied due to the differences in membrane structures. In conclusion, materials and sources of membranes affected drug dissolution profiles and the results showed membrane-drug binding effects. Proper selection of membranes with low drug binding ability and low diffusion resistance is essential to ensure appropriate and reproducible in vitro release assessments and filtration studies. Graphical Abstract.

On line kinetic analysis of permeation profiles for UV filter loaded microemulsions using an automatic system with spectroscopic detection and a chemometric approach

On-line and green automatic methods with spectrophotometric detection were developed to the obtention of permeation kinetic constants of octyl p-methoxycinnamate in o/w microemulsions. The effect of interferences was overcome using chemometric tools.

Alternatives to Biological Skin in Permeation Studies: Current Trends and Possibilities

: The transdermal route of drugs has received increased attention in recent years due to numerous advantages over the oral and injectable routes, such as avoidance of the hepatic metabolism, protection of drugs from the gastrointestinal tract, sustained drug delivery, and good patient compliance. The assessment of ex vivo permeation during the pharmaceutical development process helps in understanding the product quality and performance of a transdermal delivery system. Generally, excised human skin relevant to the application site or animal skin is recommended for ex vivo permeation studies. However, the limited availability of the human skin and ethical issues surrounding the use of animal skin rendered these models less attractive in the permeation study. In the last three decades, enormous efforts have been put into developing artificial membranes and 3D cultured human skin models as surrogates to the human skin. This manuscript provides an insight on the European Medicines Agency (EMA) guidelines for permeation studies and the parameters affected when using Franz diffusion cells in the permeation study. The need and possibilities for skin alternatives, such as artificially cultured human skin models, parallel artificial membrane permeability assays (PAMPA), and artificial membranes for penetration and permeation studies, are comprehensively discussed.

Skin models for the testing of transdermal drugs

The assessment of percutaneous permeation of molecules is a key step in the evaluation of dermal or transdermal delivery systems. If the drugs are intended for delivery to humans, the most appropriate setting in which to do the assessment is the in vivo human. However, this may not be possible for ethical, practical, or economic reasons, particularly in the early phases of development. It is thus necessary to find alternative methods using accessible and reproducible surrogates for in vivo human skin. A range of models has been developed, including ex vivo human skin, usually obtained from cadavers or plastic surgery patients, ex vivo animal skin, and artificial or reconstructed skin models. Increasingly, largely driven by regulatory authorities and industry, there is a focus on developing standardized techniques and protocols. With this comes the need to demonstrate that the surrogate models produce results that correlate with those from in vivo human studies and that they can be used to show bioequivalence of different topical products. This review discusses the alternative skin models that have been developed as surrogates for normal and diseased skin and examines the concepts of using model systems for in vitro–in vivo correlation and the demonstration of bioequivalence.

Carbon nanotube membranes to predict skin permeability of compounds

In the present study, carbon nanotube (CNT) membranes were prepared to predict skin penetration properties of compounds. A series of penetration experiments using Franz diffusion cells were performed with 16 different membrane compositions for model chemicals. Similar experiments were also carried out with same model molecules using five different commercially available synthetic membranes and human skins for the comparison. Model chemicals were selected as diclofenac, dexketoprofen and salicylic acid. Their permeability coefficients and flux values were calculated. Correlations between permeability values of model compounds for human skins and developed model membranes were investigated. Good correlations were obtained for CNT membrane, isopropyl myristate-treated CNT membrane (IM-CNT membrane) and bovine serum albumin-cholesterol, dipalmitoyl phosphatidyl choline-treated membrane (BSA-Cholesterol-DPPC-IM-CNT membrane). An artificial neural network (ANN) model was developed using some molecular properties and penetration coefficients from pristine CNT membranes to predict skin permeability values and quite good predictions were made.

Performance evaluation of Cryo Laser Phoresis technique as biophysical method to promote diclofenac sodium cutaneous perfusion

ABSTRACT Aiming to alter and/or improve permeation of active compounds in the skin, many strategies have been developed, including biophysical methods. One of the physical absorption techniques, currently known as Cryo Laser Phoresis (CLP), consists of an apparatus that emits radiation on polar or nonpolar molecules of the active substance, resulting in faster penetration when in comparison to the standard topical application. The goal of this work was to evaluate the efficacy of a method that proposes to increase cutaneous permeation of diclofenac sodium by using CLP technique. The influence on permeation was evaluated ex vivo, using Franz cell and human skin obtained from cosmetic surgery. The results were evaluated using statistical methods and data exploratory analysis: clusters, k-means and Principal Component Analysis. The results showed a larger increase in the concentration of diclofenac sodium in the dermis with the use of laser. In all samples (with or without laser application) it was observed that skin surface showed an amount of diclofenac sodium and that there was no active passage to the receptor liquid, suggesting that diclofenac sodium was not absorbed. These results indicate that CLP, when used under the conditions described in this study, is able to increase diclofenac sodium penetration and its retention into deeper layers.

The relevance of polymeric synthetic membranes in topical formulation assessment and drug diffusion study

Synthetic membranes are composed of thin sheets of polymeric macromolecules that can control the passage of components through them. Generally, synthetic membranes used in drug diffusion studies have one of two functions: skin simulation or quality control. Synthetic membranes for skin simulation, such as the silicone-based membranes polydimethylsiloxane and Carbosil, are generally hydrophobic and rate limiting, imitating the stratum corneum. In contrast, synthetic membranes for quality control, such as cellulose esters and polysulfone, are required to act as a support rather than a barrier. These synthetic membranes also often contain pores; hence, they are called porous membranes. The significance of Franz diffusion studies and synthetic membranes in quality control studies involves an understanding of the fundamentals of synthetic membranes. This article provides a general overview of synthetic membranes, including a brief background of the history and the common applications of synthetic membranes. This review then explores the types of synthetic membranes, the transport mechanisms across them, and their relevance in choosing a synthetic membrane in Franz diffusion cell studies for formulation assessment purposes.

Validation of a static Franz diffusion cell system for in vitro permeation studies

Over the years, in vitro Franz diffusion experiments have evolved into one of the most important methods for researching transdermal drug administration. Unfortunately, this type of testing often yields permeation data that suffer from poor reproducibility. Moreover, this feature frequently occurs when synthetic membranes are used as barriers, in which case biological tissue-associated variability has been removed as an artefact of total variation. The objective of the current study was to evaluate the influence of a full-validation protocol on the performance of a tailor-made array of Franz diffusion cells (GlaxoSmithKline, Harlow, UK) available in our laboratory. To this end, ibuprofen was used as a model hydrophobic drug while synthetic membranes were used as barriers. The parameters investigated included Franz cell dimensions, stirring conditions, membrane type, membrane treatment, temperature regulation and sampling frequency. It was determined that validation dramatically reduced derived data variability as the coefficient of variation for steady-state ibuprofen permeation from a gel formulation was reduced from 25.7% to 5.3% (n = 6). Thus, validation and refinement of the protocol combined with improved operator training can greatly enhance reproducibility in Franz cell experimentation.

A Comparative Study of Transmembrane Diffusion and Permeation of Ibuprofen across Synthetic Membranes Using Franz Diffusion Cells

Synthetic membranes used in Franz diffusion cells for topical formulation quality assessment should provide least resistance to drug diffusion. In this study, the diffusion rates of ibuprofen across thirteen membranes were determined using Franz diffusion cells. Correlation of the membrane thickness, pore size and MWCO with drug fluxes was also made. The drug diffusion results showed that the porous membranes were categorized into high-flux (8-18 mg/cm²/h) and low-flux (0.1-3 mg/cm²/h) membranes. The drug fluxes did not show strong correlations (r² < 0.99) with membrane parameters. Synthetic membranes can give variable drug fluxes, thus investigators should be careful in choosing membrane for formulation quality assessment.

In vitro transdermal delivery of caffeine, theobromine, theophylline and catechin from extract of Guarana, Paullinia Cupana

Extracts of guarana (Paullinia cupana) feature as putatively stimulating ingredients in a number of foods, drinks and dietary/herbal supplements. The objective of this work was to investigate in vitro the transdermal delivery of the major pharmacologically active compounds contained in guarana extract. Saturated solutions of guarana were prepared in polyethylene glycol 400 (PEG400), propylene glycol (PG) and H(2)O at 32 degrees C. Guarana extract was also formulated in Duro-tak 2287 transdermal adhesive in a range of concentrations and the diffusional release was determined in addition to adhesive properties. Transdermal delivery across full thickness pig ear skin was investigated in vitro using Franz-type diffusion cells, with reverse-phase HPLC being used for the quantification of the permeation of theobromine (TB), theophylline (TP), (+)-catechin (C) and caffeine (CF). Based upon a combination of release and adhesive property data a patch containing 5.55 mg guarana extract cm(-2) was deemed optimal. The general trend for the delivery of the 4 analytes was: water >5.55 mg cm(-2) patch approximately PG>PEG400. For CF the greatest steady state flux was obtained from the water vehicle: 19 microg cm(-2)h(-1), with approximately 420 microg cm(-2) permeating after 24h. This was some 6x times more than from the drug-in-adhesive patch and 10x greater than PG, a well-known penetration enhancer, and 50x that of the 'regular' excipient PEG400. A water vehicle also provided the greatest delivery of TB (0.45 microg cm(-2) h(-1)), TP (0.022 microg cm(-2) h(-1)), and C (0.10 microg cm(-2) h(-1)). An inverse relationship was noted between lipophilicity and k(p) in each vehicle. The simultaneous transdermal delivery of the major actives of guarana was established, with permeation rates being highly concentration and vehicle dependent.

Film drying and complexation effects in the simultaneous skin permeation of ketoprofen and propylene glycol from simple gel formulations

This work investigated the simultaneous permeation of ketoprofen and propylene glycol (PG) across pig ear skin from simple gel formulations administered under simulated in-use conditions. The aims were to quantify rates of permeation of both solvent and active, probe the effects of formulation drying and gain insight into drag/complexation interactions. Simple 3-component gels were formulated using a fixed amount of ketoprofen and hydroxypropyl cellulose thickener with decreasing content of solvent propylene glycol. Multiple finite (5 mg x 15 mg) doses were massaged over 24h into full thickness pig ear skin in vertical Franz-type diffusion cells. The permeation of ketoprofen was inversely proportional to the content of PG, whereas the permeation of PG was directly proportional, although the amount of PG permeated was always greater than ketoprofen, even from the driest gel practically achievable. In this state, the molar ratio of PG/ketoprofen was approximately 12, suggesting that this number of PG molecules constitutes the solvation cage of ketoprofen. Dragging/pulling effect extends throughout the skin and into the receptor compartment and probably the system, in an in vivo situation. Although PG may represent a worse case scenario given its well-documented skin permeation enhancement properties, it is probable that other solvents exert a similar effect on solutes across skin. A drying film will behave in different ways depending on the nature of both the thickener and solvent, where the outcomes are not readily predictable. It is important to account for the fate of all species administered from a topical formulation.

Solvent Content and Macroviscosity Effects on the in vitro Transcutaneous Delivery and Skin Distribution of Ketoprofen from Simple Gel Formulations

The effects of decreasing solvent content and macroviscosity of simple topical gel formulations on the transcutaneous delivery and distribution of ketoprofen through skin were studied. Simple topical gels, based on ketoprofen, PEG 400 and either Cabosil M-5 or hydroxypropylcellulose were formulated and applied to freshly excised pig ear skin in vitro. Receptor phase samples were taken to determine permeation and depth profiles of ketoprofen were constructed, following tape stripping and membrane separation. Reduction of solvent from the Cabosil-thickened gels resulted in a rank order reduction in the permeation and distribution of ketoprofen. Reduced amounts of ketoprofen were distributed through the skin, particularly the dermis, with decreasing solvent. Two gels sharing the same macroviscosity exhibited significantly different skin permeation and distribution characteristics. The rank order reduction in both permeation and distribution of ketoprofen was attributed to the physiochemical properties of the formulation and how they may change after application, in particular the increased adsorptivity of ketoprofen to the Cabosil relative to the amount of solvent present in the system. This effect appeared to be predominant over any interactions occurring between the formulation and the skin. The data provided further evidence that adsorption to the thickener, rather than changes in viscosity, were primarily responsible for reduced permeation and distribution in the system examined.