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.

Comparison of the in vitro release characteristics of mucosal freeze-dried wafers and solvent-cast films containing an insoluble drug.

Drug release characteristics of freeze-dried wafers and solvent-cast films prepared from sodium carboxymethylcellulose have been investigated and compared. In vitro drug dissolution studies were performed using an exchange cell and drug release was measured by UV spectroscopy at 272 nm using distilled water. The dissolution profiles of hydrochlorothiazide from the wafers and films were compared by determining the rates of drug release, estimated from the % release versus time profiles and calculating their difference (f(1)) and similarity (f(2)) factors.

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.

Characterisation of freeze-dried wafers and solvent evaporated films as potential drug delivery systems to mucosal surfaces.

Freeze-dried (lyophilised) wafers and solvent cast films from sodium alginate (ALG) and sodium carboxymethylcellulose (CMC) have been developed as potential drug delivery systems for mucosal surfaces including wounds. The wafers (ALG, CMC) and films (CMC) were prepared by freeze-drying and drying in air (solvent evaporation) respectively, aqueous gels of the polymers containing paracetamol as a model drug. Microscopic architecture was examined using scanning electron microscopy, hydration characteristics with confocal laser scanning microscopy and dynamic vapour sorption.

Transepidermal water loss for probing full-thickness skin barrier function: correlation with tritiated water flux, sensitivity to punctures and diverse surfactant exposures.

Skin barrier function is a key parameter to consider when performing in vitro percutaneous absorption studies. Whilst tritiated water flux measurements were often used to assess skin integrity, recent decades have witnessed the emergence of the more rapid and user-friendly transepidermal water loss (TEWL) approach. Yet to date, the nature of the correlation between TEWL and skin barrier function in vitro has still not been comprehensively established.

In vitro drug release studies of polymeric freeze-dried wafers and solvent-cast films using paracetamol as a model soluble drug.

Drug dissolution and release characteristics from freeze-dried wafers and solvent-cast films prepared from sodium carboxymethylcellulose (CMC) have been investigated to determine the mechanisms of drug release from the two systems. The formulations were prepared by freeze-drying (wafers) or drying in air (films), the hydrated gel of the polymer containing paracetamol as a model soluble drug. Scanning electron microscopy (SEM) was used to examine differences between the physical structure of the wafers and films.

Development and mechanical characterization of solvent-cast polymeric films as potential drug delivery systems to mucosal surfaces.

Solvent-cast films from three polymers, carboxymethylcellulose (CMC), sodium alginate (SA), and xanthan gum, were prepared by drying the polymeric gels in air. Three methods, (a) passive hydration, (b) vortex hydration with heating, and (c) cold hydration, were investigated to determine the most effective means of preparing gels for each of the three polymers. Different drying conditions [relative humidity - RH (6-52%) and temperature (3-45 degrees C)] were investigated to determine the effect of drying rate on the films prepared by drying the polymeric gels.

Factors influencing hydrocortisone permeation into human hair follicles: use of the skin sandwich system.

The aim of the present study was to use the in vitro human skin sandwich system in order to quantify the influence of formulation variables on intrafollicular hydrocortisone permeation. The investigated variables were the pH and the viscosity of the topical formulation as well as the presence of chemical enhancers (carvone, menthone, oleic acid and sodium lauryl sulphate). Furthermore, skin sandwich hydration was also varied in order to determine if the method itself can be run using only partially hydrated skin tissues.

In-vitro permeation of drugs into porcine hair follicles: is it quantitatively equivalent to permeation into human hair follicles?

It is already well-established that the general permeability properties of porcine skin are close to those of human skin. However, very little is known with respect to drug absorption into hair follicles and the similarities if any between the two types of tissue. The aim of this study was to use the skin sandwich system to quantify follicular drug absorption into porcine hair follicles.

Wound healing dressings and drug delivery systems: a review.

The variety of wound types has resulted in a wide range of wound dressings with new products frequently introduced to target different aspects of the wound healing process. The ideal dressing should achieve rapid healing at reasonable cost with minimal inconvenience to the patient. This article offers a review of the common wound management dressings and emerging technologies for achieving improved wound healing.

Evidence that drug flux across synthetic membranes is described by normally distributed permeability coefficients.

Over recent decades, the use of in vitro diffusion cell studies to assess skin permeability has evolved into a major research tool, providing key insights into the relationships between skin, drug and formulation. Sometimes, such studies involve synthetic membranes as this approach can yield useful inferences with respect to drug-skin partitioning and diffusion phenomena. Yet despite the popularity of such studies, it is still not at all known whether typical solute transport across synthetic barriers results in a normal distribution of permeability coefficients or alternatively some type of skewed distribution.

The influence of drug partition coefficient on follicular penetration: in vitro human skin studies.

The aim of this study was to employ the novel skin sandwich system in order to quantify the influence of the octanol-water partition coefficient on follicular drug absorption in human skin. To this end, seven different drugs - estradiol, corticosterone, hydrocortisone, aldosterone, cimetidine, deoxyadenosine and adenosine - exhibiting a wide range of log octanol-water partition coefficients (logK(o/w)) but relatively similar molecular weights were selected as candidate solutes. Application of the skin sandwich technique yielded an interesting relationship between % follicular contribution and logK(o/w).

Towards a correlation between drug properties and in vitro transdermal flux variability.

Over recent years, there has been growing evidence that the permeability coefficient variability describing any specific transdermal drug delivery system is not always normally distributed. However, since different researchers have used different test compounds, methodologies and skin types, it has been difficult to identify any general correlation between drug properties and flux variability. The aim of the present study was to investigate whether there was a relationship between these two variables.

Composition analysis of two batches of polysorbate 60 using MS and NMR techniques.

Batch variation in Tween 60 has shown to influence the rheological properties of semisolid emulsions. MS (LC-MS, GC-MS, MS(n)) and NMR ((13)C, (1)H, (1)H COSY and HMBC) techniques were used to analyze and compare the composition of two batches of Tween 60 with particular emphasis on the number of POE groups and their distribution within the molecule. Acid and saponification values were also determined.

Assessment of drug permeability distributions in two different model skins.

Past in vitro studies with human skin have indicated that drug permeability coefficient (Kp) distributions do not always follow a Gaussian-normal pattern. This has major statistical implications, exemplified by the fact that use of t-tests to evaluate significance is limited to normally distributed populations. Percutaneous absorption research often involves using animal or synthetic skins to simulate less readily available human skin.