In vivo methods for the assessment of topical drug bioavailability

Investigating transdermal delivery of vitamin D3

Transdermal delivery of therapeutic amounts of vitamin D3 is proposed to overcome its variable oral bioavailability, especially for people who suffer from fat malabsorption. The main challenge for this delivery route is to overcome the barrier properties of skin, especially for very lipophilic compounds such as vitamin D3. In this study, the effect of different penetration enhancers, such as oleic acid, dodecylamine, ethanol, oleic acid in propylene glycol, isopropyl myristate, octyldodecanol, and oleyl alcohol in propylene glycol were evaluated in vitro for their effectiveness in delivering vitamin D3 through polyamide filter, polydimethylsiloxane membrane, and porcine skin. A diffusion cell was used to study the transdermal permeability of vitamin D3. Ointment formulations of vitamin D3 were prepared containing the most widely used penetration enhancers, oleic acid, and dodecylamine. The ointment containing oleic acid as chemical penetration enhancer did not improve delivery compared to control. On the other hand, the formulation containing dodecylamine as a penetration enhancer did improve the transdermal delivery of vitamin D3. However, statistical significance and an amount high enough for nutritional supplementation purposes were reached only when the skin was pretreated with 50% ethanol. In these conditions, the ointment delivered an amount of 760-ng vitamin D3 per cm(2) of skin. The research shows promise that transdermal delivery could be an effective administration route for vitamin D3 when ethanol and dodecylamine are used as penetration enhancers.

Applications and limitations of lipid nanoparticles in dermal and transdermal drug delivery via the follicular route

Lipid nanoparticles (LN) such as solid lipid nanoparticles (SLN) and nanolipid carriers (NLC) feature several claimed benefits for topical drug therapy including biocompatible ingredients, drug release modification, adhesion to the skin, and film formation with subsequent hydration of the superficial skin layers. However, penetration and permeation into and across deeper skin layers are restricted due to the barrier function of the stratum corneum (SC). As different kinds of nanoparticles provide the potential for penetration into hair follicles (HF) LN are applicable drug delivery systems (DDS) for this route in order to enhance the dermal and transdermal bioavailability of active pharmaceutical ingredients (API). Therefore, this review addresses the HF as application site, published formulations of LN which showed follicular penetration (FP), and characterization methods in order to identify and quantify the accumulation of API delivered by the LN in the HF. Since LN are based on lipids that appear in human sebum which is the predominant medium in HF an increased localization of the colloidal carriers as well as a promoted drug release may be assumed. Therefore, sebum-like lipid material and a size of less or equal 640 nm are appropriate specifications for FP of particulate formulations.

Quantification of uptake and clearance of acyclovir in skin layers

BACKGROUND

Quantification of drug uptake and clearance in the skin layers could provide better insight into the skin kinetics of dermatological formulations aimed for deeper skin tissues. This study assessed the skin kinetics of acyclovir in different skin layers following topical application on the abdominal region of Wistar rats.

METHODS

In vivo skin pharmacokinetics parameters were determined by two different protocols such as post drug load assessment and subsequent drug load assessment following topical application of 500 mg of cream formulation containing 5% (w/w) of acyclovir.

RESULTS

Topical application of acyclovir exhibited concentration gradient between the skin layers (stratum corneum > viable epidermis > dermis) which were inconsistent over the time-course of the study. The rate and extent of drug reaching target site (basal epidermis) was relatively low. The drug uptake and clearance profiles were found to be distinct in all the three skin layers suggesting no drug concentration correlation (P<0.05) between skin layers. Drug concentration in the viable epidermis continued to increase even after termination of therapy (Tmax=4 h) and then declined rapidly. The availability of acyclovir in the target was comparatively low (approximately 0.4% of the applied dose) although an order of magnitude higher percentage was determined in the stratum corneum.

CONCLUSIONS

The data observed in this study demonstrates low skin uptake and rapid clearance of acyclovir in the target site. Further, the methodology employed can be useful for studying other topical antiviral agents as well as for optimizing formulations for drugs (such as acyclovir) that may enhance their efficacy.

Trials and tribulations of skin iontophoresis in therapeutics

Iontophoresis is a method of non-invasive transdermal drug delivery based on the transfer of charged molecules using a low-intensity electric current. Both local and systemic administration are possible; however, the skin pharmacokinetics of iontophoretically delivered drugs is complex and difficult to anticipate. The unquestionable theoretical advantages of the technique make it attractive in several potential applications. After a brief review of the factors influencing iontophoresis, we detail the current applications of iontophoresis in therapeutics and the main potential applications under investigation, including systemic and topical drugs and focusing on the treatment of scleroderma-related ulcerations. Finally, we address the issue of safety, which could be a limitation to the routine clinical use of iontophoresis.

Lipid nanoparticles for the topical delivery of retinoids and derivatives

Retinoids are lipophilic compounds that are highly used in cosmetics/therapeutics for skin disorders. Conventional formulations are limited by poor water solubility, high chemical/photochemical instability and the irritation of retinoids. Interestingly, lipid nanoparticles enable the administration of retinoids in aqueous media, providing drug stabilization and controlled release. Recently, it has been demonstrated that retinoids in solid lipid nanoparticles, nanostructured lipid carriers, nanoemulsions and nanocapsules can decrease degradation, improve targeting and enhance efficacy for the treatment of skin disorders. This article focuses on the formulation, fabrication, characterization and in vitro/in vivo evaluation of solid lipid nanoparticles, nanostructured lipid carriers, nanoemulsions and nanocapsules loaded with retinoids for skin administration. Furthermore, the incorporation of these lipid nanoparticles into secondary vehicles is discussed.

Development of a topical adapalene-solid lipid nanoparticle loaded gel with enhanced efficacy and improved skin tolerability

The present investigation substantiates the efficacy of adapalene loaded solid lipid nanoparticles (Ada-SLNs) in ameliorating the skin irritation potential of adapalene owing to its altered skin distribution.

Microsecond Scale Vibrational Spectroscopic Imaging by Multiplex Stimulated Raman Scattering Microscopy

Real-time vibrational spectroscopic imaging is desired for monitoring cellular states and cellular processes in a label-free manner. Raman spectroscopic imaging of highly dynamic systems is inhibited by relatively slow spectral acquisition on millisecond to second scale. Here, we report microsecond scale vibrational spectroscopic imaging by lock-in free parallel detection of spectrally dispersed stimulated Raman scattering signal. Using a homebuilt tuned amplifier array, our method enables Raman spectral acquisition, within the window defined by the broadband pulse, at the speed of 32 microseconds and with close to shot-noise limited detection sensitivity. Incorporated with multivariate curve resolution analysis, our platform allows compositional mapping of lipid droplets in single live cells, observation of intracellular retinoid metabolism, discrimination of fat droplets from protein-rich organelles in Caenorhabditis elegans, spectral detection of fast flowing tumor cells, and monitoring drug diffusion through skin tissue in vivo. The reported technique opens new opportunities for compositional analysis of cellular compartment in a microscope setting and high-throughput spectral profiling of single cells in a flow cytometer setting.

Quantitative 3D molecular cutaneous absorption in human skin using label free nonlinear microscopy

Understanding the penetration mechanisms of drugs into human skin is a key issue in pharmaceutical and cosmetics research. To date, the techniques available for percutaneous penetration of compounds fail to provide a quantitative 3D map of molecular concentration distribution in complex tissues as the detected microscopy images are an intricate combination of concentration distribution and laser beam attenuation upon deep penetration. Here we introduce and validate a novel framework for imaging and reconstructing molecular concentration within the depth of artificial and human skin samples. Our approach combines the use of deuterated molecular compounds together with coherent anti-Stokes Raman scattering spectroscopy and microscopy that permits targeted molecules to be unambiguously discriminated within skin layers. We demonstrate both intercellular and transcellular pathways for different active compounds, together with in-depth concentration profiles reflecting the detailed skin barrier architecture. This method provides an enabling platform for establishing functional activity of topically applied products.

Development of performance matrix for generic product equivalence of acyclovir topical creams

The effect of process variability on physicochemical characteristics and in vitro performance of qualitatively (Q1) and quantitatively (Q2) equivalent generic acyclovir topical dermatological creams was investigated to develop a matrix of standards for determining their in vitro bioequivalence with reference listed drug (RLD) product (Zovirax®). A fractional factorial design of experiment (DOE) with triplicate center point was used to create 11 acyclovir cream formulations with manufacturing variables such as pH of aqueous phase, emulsification time, homogenization speed, and emulsification temperature. Three more formulations (F-12-F-14) with drug particle size representing RLD were also prepared where the pH of the final product was adjusted. The formulations were subjected to physicochemical characterization (drug particle size, spreadability, viscosity, pH, and drug concentration in aqueous phase) and in vitro drug release studies against RLD. The results demonstrated that DOE formulations were structurally and functionally (e.g., drug release) similar (Q3) to RLD. Moreover, in vitro drug permeation studies showed that extent of drug bioavailability/retention in human epidermis from F-12-F-14 were similar to RLD, although differed in rate of permeation. The results suggested generic acyclovir creams can be manufactured to obtain identical performance as that of RLD with Q1/Q2/Q3.

Skin uptake and clearance of ciclopirox following topical application

The assessment of skin uptake and clearance are important to determine the efficiency and systemic safety of dermatological formulations. The objective of this study was to assess the skin uptake, clearance and possible systemic delivery of ciclopirox following topical application in Wistar rats. In vitro studies (3 h) were carried out in excised pig skin to assess the permeation and retention capacity of ciclopirox in skin layers using gel formulations (1% and 2% w/v). In vivo dermatopharmacokinetics (DPK) parameters were determined by measuring the drug levels in the skin as a function of time post application (0.5, 1, 1.5 and 2 h) and post removal (3, 4, 6 and 8 h) of the formulation in Wistar rats. The plasma drug concentrations were also determined in the same animals. In vitro data indicate the low permeability and high retention of ciclopirox in the stratum corneum. The DPK data observed indicate a higher Cmax value (175.43 ± 25.62 μg/cm2) and AUC (632.14 ± 102.26 μg.h/cm2) with the 2% (w/v) gel formulation. Further, the skin elimination of ciclopirox follows first order kinetics with a short half-life (t1/2 ~2 h). The fraction of drug reaching the systemic circulation was found to be significantly low (~0.15% of the applied dose). A relation between the drug concentration in the skin layers and the plasma was observed with a short lag period. The topical availability of ciclopirox was found to be relatively low and endured rapid clearance with minimal systemic uptake.

In vivo real-time monitoring system of electroporation mediated control of transdermal and topical drug delivery

Electroporation (EP) is a physical method for the delivery of molecules into cells and tissues, including the skin. In this study, in order to control the degree of transdermal and topical drug delivery, EP at different amplitudes of electric pulses was evaluated. A new in vivo real-time monitoring system based on fluorescently labeled molecules was developed, for the quantification of transdermal and topical drug delivery. EP of the mouse skin was performed with new non-invasive multi-array electrodes, delivering different amplitudes of electric pulses ranging from 70 to 570 V, between the electrode pin pairs. Patches, soaked with 4 kDa fluorescein-isothiocyanate labeled dextran (FD), doxorubicin (DOX) or fentanyl (FEN), were applied to the skin before and after EP. The new monitoring system was developed based on the delivery of FD to and through the skin. FD relative quantity was determined with fluorescence microscopy imaging, in the treated region of the skin for topical delivery and in a segment of the mouse tail for transdermal delivery. The application of electric pulses for FD delivery resulted in enhanced transdermal delivery. Depending on the amplitude of electric pulses, it increased up to the amplitude of 360 V, and decreased at higher amplitudes (460 and 570 V). Topical delivery steadily enhanced with increasing the amplitude of the delivered electric pulses, being even higher than after tape stripping used as a positive control. The non-invasive monitoring of the delivery of DOX, a fluorescent chemotherapeutic drug, qualitatively and quantitatively confirmed the effects of EP at 360 and 570 V pulse amplitudes on topical and transdermal drug delivery. Delivery of FEN at 360 and 570 V pulse amplitudes verified the observed effects as obtained with FD and DOX, by the measured physiological responses of the mice as well as FEN plasma concentration. This study demonstrates that with the newly developed non-invasive multi-array electrodes and with the varying electric pulse amplitude, the amount of topical and transdermal drug delivery to the skin can be controlled. Furthermore, the newly developed monitoring system provides a tool for rapid real-time determination of both, transdermal and topical delivery, when the delivered molecule is fluorescent.

Basic considerations in the dermatokinetics of topical formulations

Assessing the bioavailability of drug molecules at the site of action provides better insight into the efficiency of a dosage form. However, determining drug concentration in the skin layers following topical application of dermatological formulations is a great challenge. The protocols followed in oral formulations could not be applied for topical dosage forms. The regulatory agencies are considering several possible approaches such as tape stripping, microdialysis etc. On the other hand, the skin bioavailability assessment of xenobiotics is equally important for topical formulations in order to evaluate the toxicity. It is always possible that drug molecules applied on the skin surface may transport thorough the skin and reaches systemic circulation. Thus the real time measurement of molecules in the skin layer has become obligatory. In the last two decades, quite a few investigations have been carried out to assess the skin bioavailability and toxicity of topical/dermatological products. This review provides current understanding on the basics of dermatokinetics, drug depot formation, skin metabolism and clearance of drug molecules from the skin layers following application of topical formulations.

Retrodialysis: a review of experimental and clinical applications of reverse microdialysis in the skin

Microdialysis is a method that has been used for decades to recover endogenous mediators, metabolites and drugs from the interstitial space in several tissues of both animals and humans. The principle of microdialysis is the flux of compounds across a semipermeable membrane. The application of microdialysis as a method of drug delivery is a process referred to as retrodialysis, i.e. the introduction of a substance into the extracellular space via a microdialysis probe. Thus, microdialysis also offers opportunities to deliver mediators and drugs to target tissues by adding solutes to the perfusion medium. In this context, retrodialysis combines a method for minimally invasive delivery with a sampling method to study biological processes in health and disease. The aim of this review is to give insight into the use of retrodialysis by outlining examples of retrodialysis studies focusing on applications in skin in animal studies, human experimental investigations and clinical settings.

Clinical applicability of dOFM devices for dermal sampling

BACKGROUND

Sampling the dermal interstitial fluid (ISF) allows the pharmacokinetics and pharmacodynamics of dermatological drugs to be studied directly at their site of action. Dermal open-flow microperfusion (dOFM) is a recently developed technique that can provide minimally invasive, continuous, membrane-free (thus unfiltered) access to the dermal ISF. Herein, we evaluate the clinical applicability and reliability of novel wearable dOFM devices in a clinical setting.

METHODS

Physicians inserted 141 membrane-free dOFM probes into the dermis of 17 healthy and psoriatic volunteers and sampled dermal ISF for 25 h by using wearable push-pull pumps. The tolerability, applicability, reproducibility, and reliability of multiple insertions and 25 h continuous sampling was assessed by pain scoring, physician feedback, ultrasound probe depth measurements, and 25 h-drift and variability of the sodium relative recovery.

RESULTS

Insertion pain was moderate and decreased with each additional probe. Probe insertion was precise, although slightly deeper in lesional skin. The wearable push-pull pump enabled uninterrupted ISF sampling over 25 h with low variability. The relative recovery was drift-free and highly reproducible.

CONCLUSION

dOFM sampling devices are tolerable and reliable for prolonged continuous dermal sampling in a multiprobe clinical setting. These devices should enable the study of a wide range of drugs and their biomarkers in the skin.

Enhanced human tissue microdialysis using hydroxypropyl-ß-cyclodextrin as molecular carrier

Microdialysis sampling of lipophilic molecules in human tissues is challenging because protein binding and adhesion to the membrane limit recovery. Hydroxypropyl-ß-cyclodextrin (HP-ß-CD) forms complexes with hydrophobic molecules thereby improving microdialysis recovery of lipophilic molecules in vitro and in rodents. We tested the approach in human subjects. First, we determined HP-ß-CD influences on metabolite stability, delivery, and recovery in vitro. Then, we evaluated HP-ß-CD as microdialysis perfusion fluid supplement in 20 healthy volunteers. We placed 20 kDa microdialysis catheters in subcutaneous abdominal adipose tissue and in the vastus lateralis muscle. We perfused catheters with lactate free Ringer solution with or without 10% HP-ß-CD at flow rates of 0.3–2.0 µl/min. We assessed tissue metabolites, ultrafiltration effects, and blood flow. In both tissues, metabolite concentrations with Ringer+HP-ß-CD perfusate were equal or higher compared to Ringer alone. Addition of HP-ß-CD increased dialysate volume by 10%. Adverse local or systemic reactions to HP-ß-CD did not occur and analytical methods were not disturbed. HP-ß-CD addition allowed to measure interstitial anandamide concentrations, a highly lipophilic endogenous molecule. Our findings suggest that HP-ß-CD is a suitable supplement in clinical microdialysis to enhance recovery of lipophilic molecules from human interstitial fluid.

Enhanced dermal delivery of diflucortolone valerate using lecithin/chitosan nanoparticles: in-vitro and in-vivo evaluations

The objective of this study was to prepare a suitable formulation for dermal delivery of diflucortolone valerate (DFV) that would maintain the localization in skin layers without any penetration and to optimize efficiency of DFV. Drug-loaded lecithin/chitosan nanoparticles with high entrapment efficiency (86.8%), were successfully prepared by ionic interaction technique. Sustained release of DFV was achieved without any initial burst release. Nanoparticles were also incorporated into chitosan gel at different ratios for preparing a more suitable formulation for topical drug delivery with adequate viscosity. In ex-vivo permeation studies, nanoparticles increased the accumulation of DFV especially in the stratum corneum + epidermis of rat skin without any significant permeation. Retention of DFV from nanoparticle in chitosan gel formulation (0.01%) was twofold higher than commercial cream, although it contained ten times less DFV. Nanoparticles in gel formulations produced significantly higher edema inhibition in rats compared with commercial cream in in-vivo studies. Skin blanching assay using a chromameter showed vasoconstriction similar to that of the commercial product. There were no barrier function changes upon application of nanoparticles. In-vitro and in-vivo results demonstrated that lecithin/chitosan nanoparticles in chitosan gel may be a promising carrier for dermal delivery of DFV in various skin disorders.

Influence of skin type, race, sex, and anatomic location on epidermal barrier function

The intact skin represents a barrier to the uncontrolled loss of water, proteins, and plasma components from the organism. Owing to its complex structure, the epidermal barrier with its major layer, the stratum corneum, is the rate-limiting unit for the penetration of exogenous substances through the skin. The epidermal barrier is not a static structure. The status of different functions of the epidermis can be monitored by assessing specific biophysical parameters such as transepidermal water loss, stratum corneum hydration, and skin surface pH. Variables originating from the individual as well as exogenous factors have an important influence on the epidermal barrier parameters.

Challenges obtaining a biowaiver for topical veterinary dosage forms

Obtaining a biowaiver for topical drugs used in veterinary species faces many of the same challenges associated with human topicals. However, the skin of domestic animals varies anatomically and biochemically and experimental approaches to assess bioequivalence (BE) in veterinary species have challenges that are not often encountered with human skin. This is especially the situation with locally acting drugs. The focus of this paper is to address several of the challenges associated with (i) determining the BE of these locally acting drugs and (ii) critically examine the current technological advances that can act as a surrogate for clinical trials.

Targeting tacrolimus to deeper layers of skin with improved safety for treatment of atopic dermatitis-Part II: in vivo assessment of dermatopharmacokinetics, biodistribution and efficacy

The objective of present investigation was to study in vivo behavior of tacrolimus-loaded lipid-nanoparticles (T-LN) to understand its targeting potential for treatment of atopic-dermatitis-(AD). T-LN have shown significantly improved drug penetration to deeper epidermal and dermal skin-layers than commercial ointment-Protopic(®) and effectively reached target dendritic-immune-cells, responsible for immunopathogenesis of AD. Due to enhanced penetrability of T-LN, it became necessary to evaluate the toxicity of the nanocarrier and the drug at non-target tissues. This paper evaluates dermatopharmacokinetics (DPK), biodistribution, efficacy and safety of T-LN in comparison to Protopic(®) as reference. In vivo DPK in guinea pigs showed 3.02-fold higher bioavailability while γ-scintigraphy in albino-rats demonstrated 1.5-fold rapid penetration of radioactivity in skin for T-LN. Biodistribution in albino-rats revealed restricted localization at the target-skin-area with no general spreading to other body organs suggesting targeting potential of T-LN. In vivo efficacy studies in BALB/c mice showed highly efficient suppression of inflammatory AD-like skin-lesions with T-LN than reference and placebo. Dermal toxicity-studies revealed keratosis and collagenous mass-infiltration with repeated application of reference however interestingly, T-LN treated group showed no evident toxicity demonstrating significantly improved safety. Thus T-LN offered improved penetration to the target site without any toxic-effects and would represent an efficient and commercially viable alternative for AD treatment.

Generic drugs in dermatology: part I

The cost of health care in the United States is increasing. In order to help control these rising costs, all parties involved in the delivery of health care, including dermatologists, need to be part of the solution of ethically reducing the cost of delivery of care. One potential means of meeting this goal is to increase the use of generic medications in daily practice. Generic medications can offer equally efficacious therapy at significantly lower prices, which can translate into large scale savings for the individual patient, the payer, and the overall health care system. Herein we provide an overview of new drug development, review the history of the generic drug industry, describe how generic drugs are approved by the US Food and Drug Administration, and define the concepts of bioequivalence and therapeutic equivalence. In part II, we explore various factors impacting generic drug use, provide cost analyses of dermatologic brand name and generic drugs, and review data addressing potential differences in the effectiveness of brand name versus generic drugs in dermatology. The cost of brand name and generic medications is highly variable by pharmacy, state, and payer. We used one source (www.drugstore.com) as an example and for consistency across all medications discussed herein. Prices included here may not reflect actual retail prices across the United States.

In vivo monitoring of epidermal absorption of hazardous substances by confocal Raman micro-spectroscopy

BACKGROUND

Presently, percutaneous absorption of potentially hazardous chemicals in humans can only be assessed in animal experiments, in vitro, or predicted mathematically. Our aim was to demonstrate the proof-of-principle of a novel quantitative in vivo assay for percutaneous absorption: confocal Raman micro-spectroscopy (CRS). The advantages and limitations of CRS for health risk assessments are discussed.

PATIENTS AND METHODS

2-butoxyethanol, toluene, and pyrene were applied in pure form, diluted in water, or in ethanol on the skin of three healthy volunteers. CRS measurements were done following application for 15 min and 3 hours. The concentrations of the three substances as a function of distance to the skin surface were calculated and further analyzed with regard to mass transport into the stratum corneum (μg/cm(2)) and the flux through the stratum corneum (μg/cm(2)h). The results were compared with the available data from literature.

RESULTS

Considering the preliminary nature of these data, good accordance with data from the literature was observed. In addition, we observed that 2-butoxyethanol penetrates markedly faster when dissolved in water as compared to ethanol. This observation is also in agreement with previous results.

CONCLUSIONS

CRS has the potential to provide fast, accurate and reliable results for advanced studies of in vivo percutaneous absorption kinetics of hazardous substances in human skin. This will require further research with other substances and under differing conditions.

Microdialysis documents changes in the micromilieu of psoriatic plaques under continuous systemic therapy

Microdialysis is a novel technique suitable to analyse soluble mediators in the skin compartment. We applied this methodical approach to monitor changes in the micromilieu of psoriatic plaques under therapy. Tissue fluid was collected from lesional and non-lesional skin of three patients with severe plaque-type psoriasis prior to as well as after 12 weeks of continuous oral therapy with fumaric acid esters. Concentrations of a spectrum of cytokines and adipokines were measured using a commercial fluorescent bead immunoassay. The procedure was well tolerated even without local anaesthesia. Prior to initiation of therapy, we found elevated levels for IL-2, IL-6, IL-18, IL-23, and resistin in lesional versus non-lesional skin, whereas adiponectin levels were higher in non-lesional skin. All patients showed significant clinical improvement under treatment, paralleled by reduced concentrations of IL-6, IL-18, IL-23, and resistin, but not IL-2 and adiponectin in lesional skin. Thus, we were able to demonstrate through microdialysis a shift in the micromilieu of psoriatic plaques, characterized by reduced levels of pro-inflammatory mediators in three patients under effective systemic anti-inflammatory therapy with fumaric acid esters. Our observations need to be confirmed by larger studies. This approach is limited by practical aspects as it is very time-consuming, but suitable to directly explore pathomechanisms causing the psoriatic phenotype in general and insulin resistance in the skin compartment in particular.

Imaging drug delivery to skin with stimulated Raman scattering microscopy

Efficient drug delivery to the skin is essential for the treatment of major dermatologic diseases, such as eczema, psoriasis and acne. However, many compounds penetrate the skin barrier poorly and require optimized formulations to ensure their bioavailability. Here, stimulated Raman scattering (SRS) microscopy, a recently developed, label-free chemical imaging tool, is used to acquire high resolution images of multiple chemical components of a topical formulation as it penetrates into mammalian skin. This technique uniquely provides label-free, nondestructive, three-dimensional images with high spatiotemporal resolution. It reveals novel features of (trans)dermal drug delivery in the tissue environment: different rates of drug penetration via hair follicles as compared to the intercellular pathway across the stratum corneum are directly observed, and the precipitation of drug crystals on the skin surface is visualized after the percutaneous penetration of the cosolvent excipient in the formulation. The high speed three-dimensional imaging capability of SRS thus reveals features that cannot be seen with other techniques, providing both kinetic information and mechanistic insight into the (trans)dermal drug delivery process.

Assessment of dermal exposure to pesticide residues during re-entry

Currently, the determination of health risks to pesticide applicators from dermal exposure to these chemicals is assessed using either a concentrate of the compound or a relevant aqueous dilution. Neither of these conditions reflects a normal exposure of an individual when re-entering an area after pesticide application, that is, contact with dried residue of the diluted product on foliage. Methodology has therefore been developed to determine a relevant estimate of this potential dermal re-entry exposure from pesticide residues. Potential delivery platforms have been characterized for the transfer of pesticide residue to skin. Spin coating has been used to deposit uniform pesticide layers on to each platform. Five pesticides have been chosen to encompass a wide range of physicochemical properties: atrazine, 2,4-dichlorophenoxyacetic acid (2,4-D), chlorpyrifos, monocrotophos, and acetochlor. In vitro (Franz diffusion cell) experiments have been performed to monitor the transfer of these pesticides from the delivery platforms onto and through excised porcine skin. Parallel experiments were also conducted with aqueous pesticide dilutions for comparison, and a final in vivo measurement using ibuprofen (as a model compound) complemented the in vitro data. The results demonstrate that transfer of chemical residue onto and subsequently through the skin is dependent on the physical attributes of the residue formed. Thus, assessing dermal exposure to pesticides based on skin contact with either the chemical concentrate or a relevant aqueous dilution may incorrectly estimate the risk for re-entry scenarios.

Assessment of topical bioequivalence using dermal microdialysis and tape stripping methods

PURPOSE

To assess the bioequivalence of two commercial topical formulations of oxytetracycline HCl by tape stripping and microdialysis in healthy volunteers.

METHODS

Tape stripping study was conducted on 12 healthy volunteers. After a 30-minute application of the formulations, adhesive tapes were used to sample stratum corneum at 0.25, 0.5, 1, 1.5, 2, 3, 4 hr. Ten of these volunteers were included in the microdialysis study with a period of 4 weeks between the experiments. Microdialysis probes were inserted into the dermis of the forearm. Following the application of the test and reference simultaneously, dialysates were collected in 30-minute sampling intervals up to 4 hr.

RESULTS

Pharmacokinetic evaluation by microdialysis yielded that the test could not be said to be bioequivalent to the reference at 90% CI. The intersubject variability of oxytetracycline content in stratum corneum was moderate when it was compared to the dermal levels. The test was found to be bioequivalent to reference according to the dermatopharmacokinetic evaluation by tape stripping.

CONCLUSIONS

No significant correlations were found between microdialysis and tape stripping methods as regarding the topical bioequivalence of oxytetracycline HCl formulations.

Development and evaluation of colloidal modified nanolipid carrier: application to topical delivery of tacrolimus

Low solubility of tacrolimus in carrier matrix and subsequent poor in vivo bioavailability was overcome by constructing modified nanolipid carrier (MNLC) as a novel approach. The aim of this study was to develop MNLC with enhanced drug solubility in carrier lipid matrix using lipophilic solubilizers for topical delivery. Comprehensive characterization of tacrolimus-loaded MNLC (T-MNLC) was carried out for particle size, morphology, and rheology. Lipid modification resulted in the formation of less perfect crystals offering space to accommodate the dissolved drug leading to high entrapment efficiency of 96.66%. Compatibility and mixing behavior of carrier constituents was evaluated using DSC, FT-IR, and (1)H NMR. T-MNLC displayed sufficient stability that could be attributed to possibility to reduce total lipid concentration in carrier. T-MNLC-enriched gels showed significantly higher in vitro drug release, skin permeation, and in vivo bioavailability with dermatopharmacokinetic approach in guinea pigs compared to commercial ointment, Protopic® as reference. Penetration-enhancing effect was confirmed using gamma scintigraphy in vivo in rats. Radioactivity remained localized in skin at the application site avoiding unnecessary biodisposition to other organs with prospective minimization of toxic effects. Skin irritation studies showed T-MNLC to be significantly less irritating than reference. Research work could be concluded as successful development of novel T-MNLC using lipophilic solubilizers to increase the encapsulation efficiency of colloidal lipid carriers with advantage of improved performance in terms of stability and skin localization.

Clinical pharmacology for development of topical dermatological products: present and future opportunities for safety and efficacy

The development of topical products for dermatological diseases represents an untapped opportunity for the clinical pharmacologist. Assessment of bioavailability of topical drugs and its utility in weighing benefit vs. risk has been unique and challenging, compared with assessments for conventional systemic drugs. However, with continued advances in analytical methods and growing interests in discovering biomarkers, the future opportunities for clinical pharmacology to advance topical drug development processes are enormous and will be limited only by our drive and determination to push science forward.

State of the art in non-invasive imaging of cutaneous melanoma

BACKGROUND

This review focuses on looking at recent developments in the non-invasive imaging of skin, in particular at how such imaging may be used at present or in the future to detect cutaneous melanoma.

METHODS

A MEDLINE search was performed for papers using imaging techniques to evaluate cutaneous melanoma, including melanoma metastasis.

RESULTS

Nine different techniques were found: dermoscopy, confocal laser scanning microscopy (including multiphoton microscopy), optical coherence tomography, high frequency ultrasound, positron emission tomography, magnetic resonance imaging, and Fourier, Raman, and photoacoustic spectroscopies. This review contrasts the effectiveness of these techniques when seeking to image melanomas in skin.

CONCLUSIONS

Despite the variety of techniques available for detecting melanoma, there remains a critical need for a high-resolution technique to answer the question of whether tumours have invaded through the basement membrane.

Evidence of deep percutaneous penetration associated with anti-inflammatory activity of topically applied Helicteres gardneriana extract: a photoacoustic spectroscopy study

PURPOSE

To apply the photoacoustic spectroscopy technique to investigate the penetration rate of topically applied Helicteres gardneriana extract used as anti-inflammatory agent.

METHODS

Experiments were performed ex vivo in a well-controlled group of mice. The crude extract was obtained from leaves of the plant Helicteres gardneriana. Croton oil was applied into the ventral surface of the mouse's right and left auricles in order to induce an inflammatory response. The left auricle was treated with crude extract, while the right one served as the control. After 6 h, the auricles were sectioned for measurements of edema intensity, myeloperoxidase activity and the formulation penetration rate.

RESULTS

Croton oil induced inflammatory response in both auricles. The application of Helicteres gardneriana extract reduced significantly the edema of the auricle and inhibited the activity of the myeloperoxidase enzyme. The photoacoustic data showed that the propagation of the formulation was efficient to reach the deep region of the auricle, crossing the cartilage. The strong anti-inflammatory effect was associated with the observed deep penetration of the formulation.

CONCLUSION

This pre-clinical study showed the anti-inflammatory effect of Helicteres gardneriana extract. The photoacoustic technique was useful to demonstrate that this anti-inflammatory activity was associated with deep percutaneous penetration.