Part 2. Comparison of emergency washing solutions in 70% hydrofluoric acid-burned human skin in an established ex vivo explants model

Background: Hydrofluoric acid (HF) is a small and partially dissociated acid (pK_a 3.2), able to deeply penetrate into human skin in addition to the corrosiveness of the hydrogen ion (H⁺) and the toxicity of the fluoride ion (F^?). However, there has been a lack of experimental studies to objectively characterize the results of human HF skin exposure decontamination.

Methodology/principal findings: A previously established experimental method using a human skin explants ex vivo model (Part 1. Experimental 70% hydrofluoric acid (HF) burns: Histological observations in an established human skin explants ex vivo model) described the lesions that appeared following 70% HF penetration. Within 5?min, 70% HF penetrates to the dermis. Using the same experimental conditions, a comparison study of two different washing protocols was performed: water + topical calcium gluconate (CaG) versus Hexafluorine^®. In these conditions, washing for 15?min with running tap water followed by topical CaG ointment only delayed burn onset, while severe tissue damage appeared later. In contrast, after washing with Hexafluorine^® over 10?min, no histological lesions developed. These results are in accordance with the results of accidental human industrial case reports.

Conclusion/significance: Amphoteric and hypertonic Hexafluorine^® can deactivate H⁺ and chelate F^? ions. Based on these results, it should be considered as a promising first-aid decontamination solution to prevent or minimize significant local and systemic consequences of concentrated HF skin exposures.     

In vitro skin decontamination model: comparison of salicylic acid and aminophylline

Objective: This study compared three model decontaminant solutions (distilled water, 10% distilled water and soap and methanol) for their ability to remove salicylic acid and aminophylline from an in vitro skin model.

Materials and methods: Human abdominal skin was dosed with 20?µL of either [¹⁴C]-aminophylline or [¹⁴C]-salicylic acid on 1?cm² per skin. After each exposure time (5, 30 and 60?min post-dosing, respectively), surface skin was washed three times with each solution and tape stripped 10 times. Wash solutions, tape strips, receptor fluid and remaining skin were then analyzed with liquid scintillation counting to quantify the amount of salicylic acid and aminophylline.

Results: Total mass balance recovery for each chemical at three time exposure points was between 73.6 and 101.5%, except at 60?min where aminophylline was only 42.5%. Majority of salicylic acid and aminophylline were recovered from washing solution when compared to stratum corneum, epidermis, dermis, surrounding skin and receptor fluid.

Conclusion: The three tested decontaminates possessed similar effectiveness in removing lipophilic and hydrophilic chemicals from the skin. Due to diminishing decontamination efficacy with time, it is suggested that skin should be washed as soon as possible following contamination to minimize percutaneous penetration and the deleterious effects associated with skin reservoir content.     

Decontamination efficacy of soapy water and water washing following exposure of toxic chemicals on human skin

Abstract

Aim of the study: Following exposure to toxic chemicals, skin uptake is a potential route of intoxication. Therefore, efficient methods for rapid skin decontamination to mitigate systemic effects are of utmost importance. In operational guidelines, skin decontamination is recommended to be performed by dry absorption and washing with water or soapy water. In the present study, evaluation of decontamination efficacy using water or soapy water was performed for five chemicals, three toxic industrial chemicals and two simulants for chemical warfare agents.

Materials and methods: Decontamination was initiated at time points 5, 15, 45 and 120 min after exposure in order to evaluate the time window for efficient decontamination. Experiments were conducted utilizing an in vitro skin penetration model to allow exposure of toxic chemicals on human skin.

Results: For all test substances, it was clearly demonstrated that decontamination had greater efficacy when initiated at the earliest time-point while decontamination after 120 min was less efficient. Adding soap to the water showed no significant improvement for any of the tested substances.

Conclusion: These results are of reledvance for the development of efficient operational decontamination procedures.     

In vitro skin penetration of acetyl hexapeptide-8 from a cosmetic formulation

There is a concern that peptides in cosmetic creams marketed as anti-aging/anti-wrinkle may penetrate into the deep layers of the skin and potentially stimulate biological activity. Claims for one cosmetic peptide, acetyl hexapeptide-8 (Ac-EEMQRR-amide), suggest interference with neuromuscular signaling as its anti-wrinkle mechanism of action. Therefore, the skin penetration of commercially available Ac-EEMQRR-amide from a cosmetic formulation (oil-in-water (O/W) emulsion) was determined in hairless guinea pig (HGP) and human cadaver skin assembled into in vitro diffusion cells. An O/W emulsion containing 10% Ac-EEMQRR-amide was applied to skin at a dose of 2?mg/cm². After a 24-h exposure, the skin surface was washed to remove unabsorbed peptide. Skin disks were tape stripped to determine the amount of peptide in the stratum corneum. Removal of the stratum corneum layers was verified by confocal microscopy. The epidermis was heat separated from the dermis and each skin fraction was homogenized. Skin penetration of Ac-EEMQRR-amide was measured in skin layers by hydrophilic interaction liquid chromatography with tandem mass spectrometry using electrospray ionization (ESI) in the positive mode. Stable isotopically labeled hexapeptides were used as internal standards for the quantitation of native hexapeptides to correct for matrix effects associated with ESI. The results (percent of applied dose) showed that the majority of the Ac-EEMQRR-amide was washed from the surface of both HGP and human skin. Ac-EEMQRR-amide that penetrated skin remained mostly in the stratum corneum of HGP (0.54%) and human (0.22%) with the peptide levels decreasing as each layer was removed by tape stripping. Total Ac-EEMQRR-amide found in the epidermis of HGP and human skin was similar at 0.01%. No peptide was detected in the dermis or buffer collected underneath the skin for both human and HGP. There was no hexapeptide metabolite (H₂N-EEMQRR-amide) detected in any layers of HGP skin, human skin or buffer collected underneath the skin. This skin penetration data will be useful for evaluating the safety of cosmetic products containing small peptide cosmetic ingredients.     

Skin decontamination efficacy of potassium ketoxime on rabbits exposed to sulfur mustard

Context: The chemical weapon sulfur mustard (SM) is a blister agent, and currently, there is no effective antidote.

Objective: To evaluate the decontamination efficacy of potassium ketoxime against SM and preliminarily elucidate its decontamination mechanism.

Materials and methods: Potassium ketoxime reacted with SM, and SM residues were tested at different time intervals by T-135 colorimetry after the reaction. Rabbit skin was topically exposed to 2?mg/cm² SM, treated with potassium ketoxime 1?min later, and observed after 6, 12, and 24?h. Gas chromatography–mass spectroscopy was employed to screen and identify the main products of potassium ketoxime decontamination of SM.

Results: Potassium ketoxime had a great effect against SM contamination. With a mass ratio of decontaminant: SM of 50:1, decontamination rates against SM were 87.5% after 30?s, 95.9% after 1?min, and 99.0% after 5?min. Fifteen minutes after exposure to SM, the untreated group showed clear erythema lesions, whereas the experimental group showed no clear erythema lesions within 6?h. After 12 and 24?h, the areas of damaged skin in the experimental group were 0.038 and 0.125?cm², respectively, compared with 2.21 and 2.65?cm² in the control group. Histopathological analysis revealed that treatment with potassium ketoxime also reduced inflammation-induced damage.

Conclusion: The results of this study indicate that potassium ketoxime reacted rapidly and completely with SM, and thus, it was found to be a suitable and effective skin decontaminant against SM. The decontamination reaction mechanism is mainly related to nucleophilic substitution.     

Analysis of Simultaneous Transport and Metabolism of Ethyl Nicotinate in Hairless Rat Skin

Purpose. Simultaneous skin transport and metabolism of ethyl nicotinate (EN), a model drug, were measured and theoretically analyzed. Methods. Several permeation studies of EN or its metabolite nicotinic acid (NA) were done on full-thickness skin or stripped skin with and without an esterase inhibitor. Permeation parameters such as partition coefficient of EN from the donor solution to the stratum corneum and diffusion coefficients of EN and NA in the stratum corneum and the viable epidermis and dermis were determined by these studies. Enzymatic parameters (Michaelis constant K _m and maximum metabolism rate V _max were obtained from the production rate of NA from different concentrations of EN in the skin homogenate. Obtained permeation data were then analyzed by numerical method based on differential equations showing Fick's second law of diffusion in the stratum corneum and the law with Michaelis-Menten metabolism in the viable epidermis and dermis. Results. Fairly good steady-state fluxes of EN and NA through the skin were obtained after a short lag time for all the concentrations of EN applied. These steady-state fluxes were not proportional to the initial donor concentration of EN: EN and NA curves were concave and convex, respectively, which suggests that metabolic saturation from EN to NA takes place in the viable skin at higher EN application. The steady-state fluxes of EN and NA calculated by the differential equations with resulting permeation and enzymatic parameters were very close to the obtained data. Conclusions. The present method is a useful tool to analyze simultaneous transport and metabolism of many drugs and prodrugs, especially those showing Michaelis-Menten type-metabolic saturation in skin.     

Effects of soap–water wash on human epidermal penetration

Skin decontamination is a primary interventional method used to decrease dermal absorption of hazardous contaminants, including chemical warfare agents, pesticides and industrial pollutants. Soap and water wash, the most common and readily available decontamination system, may enhance percutaneous absorption through the “wash‐in effect.” To understand better the effect of soap–water wash on percutaneous penetration, and provide insight to improving skin decontamination methods, in vitro human epidermal penetration rates of four C¹⁴‐labeled model chemicals (hydroquinone, clonidine, benzoic acid and paraoxon) were assayed using flow‐through diffusion cells. Stratum corneum (SC) absorption rates of these chemicals at various hydration levels (0–295% of the dry SC weights) were determined and compared with the results of the epidermal penetration study to clarify the effect of SC hydration on skin permeability. Results showed accelerated penetration curves of benzoic acid and paraoxon after surface wash at 30 min postdosing. Thirty minutes after washing (60 min postdosing), penetration rates of hydroquinone and benzoic acid decreased due to reduced amounts of chemical on the skin surface and in the SC. At the end of the experiment (90 min postdosing), a soap–water wash resulted in lower hydroquinone penetration, greater paraoxon penetration and similar levels of benzoic acid and clonidine penetration compared to penetration levels in the non‐wash groups. The observed wash‐in effect agrees with the enhancement effect of SC hydration on the SC chemical absorption rate. These results suggest SC hydration derived from surface wash to be one cause of the wash‐in effect. Further, the occurrence of a wash‐in effect is dependent on chemical identity and elapsed time between exposure and onset of decontamination. By reducing chemical residue quantity on skin surface and in the SC reservoir, the soap–water wash may decrease the total quantity of chemical absorbed in the long term; however, the more immediate accelerated absorption of chemical toxins, particularly chemical warfare agents, may be lethal. Copyright © 2015 John Wiley & Sons, Ltd.     

Microdialysis Technique as a Method to Study the Percutaneous Penetration of Methyl Nicotinate Through Excised Human Skin,Reconstructed Epidermis,and Human Skin In Vivo

Purpose. The aim was to assess the feasibility of cutaneousmicrodialysis as a method to study percutaneous penetration of methyl nicotinatethrough human skin in vitro and in vivo. Methods. Microdialysis was applied in vitro in excised human skin,in isolated dermis, in reconstructed human epidermis and in vivo inthe volar forearm skin of volunteers using methyl nicotinate (MN) asa model compound. After topical application of MN, aliquots of theperfusate were collected and analyzed for the presence of MNspectrophotometrically and by HPLC. In vivo, visual scoring and laser Dopplerperfusion imaging (LDPI) were used to monitor the effects on skinblood flow. Results. In vitro, MN was detected in the dialysate after a 1 minexposure of excised skin to concentrations as low as 25 mM. Higherconcentrations up to 500 mM showed increased levels. Prolongationof the application time to 60 min resulted in increased levels of MNin the perfusate as the duration of application increased. Reconstructedepidermis and isolated dermis showed an almost 2- and 20-fold higherpenetration compared to excised skin, respectively. In vivo, LDPImeasurements showed a rapid increase in skin blood flow afterapplication of 25 to 100 mM MN for 1 min. MN was only detectable inthe microdialysate after application of 100 mM for 10 min (two ofthree subjects). Conclusions. Cutaneous microdialysis may be a tool for comparativestudies linking responses in human skin in vivo to in vitro data usingthe same technique and endpoint.     

Comparative Analysis of Percutaneous Absorption Enhancement by d-Limonene and Oleic Acid Based on a Skin Diffusion Model

Percutaneous absorption-enhancing effects of d-limonene and oleic acid were investigated using three model drugs with different lipophilicities in in vitro diffusion experiments with guinea pig skin. Pretreatment of the skin with d-limonene resulted in a large penetration enhancement for the lipophilic butylparaben (BP) and amphiphilic 6-mercaptopurine (6-MP) but had little effect on the hydrophilic mannitol (MT). Oleic acid caused a large effect only on 6-MP penetration. The penetration profiles were analyzed with a two-layer skin diffusion model consisting of stratum corneum with polar and nonpolar routes and viable epidermis plus dermis. Through curve-fitting, six parameters corresponding to drug diffusivity and partitioning in these three regions of the skin were obtained, and the mechanisms of enhancers were assessed in comparison with those of l-geranylazacycloheptan-2-one (GACH) reported previously. Increased penetration was caused mainly by modification of the barrier property of the nonpolar route in the stratum corneum in all cases. In the nonpolar route, d-limonene increased mainly drug diffusivity, while GACH enhanced predominately drug partitioning. On the other hand, oleic acid moderately increased both parameters.     

In Vivo and in Vitro Analysis of Skin Penetration Enhancement Based on a Two-Layer Diffusion Model with Polar and Nonpolar Routes in the Stratum Corneum

In vitro and in vivo skin penetration of three drugs with different lipophilicities and the enhancing effects of l-geranylazacycloheptan-2-one (GACH) were studied in rats. In vivo drug absorption profiles obtained by deconvolution of urinary excretion profiles were compared to the corresponding in vitro data obtained with a diffusion experiment. In vivo skin penetration of lipophilic butylparaben was considerably greater than that observed in vitro, while hydrophilic mannitol and acyclovir showed low penetration in both systems without GACH pretreatment. On the other hand, GACH enhanced mannitol and acyclovir penetration, especially in the in vivo system. Analysis of absorption profiles, using a two-layer skin model with polar and nonpolar routes in the stratum corneum, suggested that the diffusion length of a viable layer (viable epidermis and dermis) was shorter in vivo than in vitro and the effective area of the polar route in the stratum corneum was larger in vitro without GACH pretreatment. GACH increased the partitioning of acyclovir into the nonpolar route to the same extent in both systems. In addition, GACH increased the effective area of the polar route in vivo, probably because of enhanced water permeability; however, this effect was smaller in vitro since the stratum corneum was already hydrated even without GACH pretreatment.     

Recent knowledge: Concepts of dermal absorption in relation to skin decontamination

Skin decontamination is an important step mitigating percutaneous absorption through the stratum corneum (SC), which is also a highly complex process. Thus, understanding diffusion mechanisms and measuring dermal absorption rates are critical to protect humans from toxic exposures. Here, highly varied literature is placed in a biological and clinical perspective in regards to decontamination. Literature from PubMed and Surge Laboratory library files were searched and reviewed for relevance. Recent data have shown multiple layers of SC structural heterogeneity, which results in unique substance partitioning characteristics across the membrane. As such, attempts to model and understand this behavior in alternative in vitro membranes prove difficult. More synthetic and natural membranes are being explored as models for in vivo behavior. In addition, commonly accepted decontamination methods are undergoing risk assessment. These recent and varied literature findings update available knowledge regarding skin decontamination and its challenges, with a focus on dermal absorption. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of TLR-2, TLR-4, and antimicrobial peptide levels in different lesions of acne vulgaris

Context: Recent studies have shown that tolls like receptors (TLRs) and antimicrobial peptides (hBD-1, cathelicidin) play an important role in the pathogenesis of acne vulgaris (AV).

Objective: To evaluate and report the expression of TLR-2, TLR-4, hBD-1 and cathelicidin in different regions of skin in AV.

Participants: This study was performed in 80 patients with AV and a control group of 20 healthy individuals.

Material and methods: Skin biopsies were performed from 20 papular, 20 pustular, 20 comedonal and 20 nodular lesions of patients and 20 healthy volunteers. Expression levels of TLR-2, TLR-4, hBD-1 and cathelicidin in four separate areas (epidermis, dermis, inflammation region and skin appendages) were evaluated by immunohistochemical method. Further, these parameters were compared between different skin lesions.

Results: A significant difference was found between the levels of staining of TLR-2, TLR-4 and hBD-1 from the epidermis, inflammation region, dermis and skin appendages (p?<?0.05). Levels of cathelicidin were different in only the inflammation region (p?<?0.05). The level of TLR-2 in the epidermis with nodules was lower than the papules and comedones (p?<?0.05). Levels of TLR-2 in the inflammation and dermis of the cases with papules were significantly higher when compared to pustules (p?<?0.05). The levels of staining of TLR-4 in the dermis with comedones were significantly lower compared to the cases with papules (p?<?005). The level of hBD-1 in the epidermis region of comedones was significantly higher compared to nodules (p?<?0.05). The expression of cathelicidin in the inflammation region of comedones was significantly low (p?<?0.05).

Conclusion: It is thought that TLR-2, TLR-4, hBD-1 and cathelicidin play an important role in the pathogenesis of AV and in the development of different acne types. We think that, better results could be obtained in treatment of AV with different treatment options targeted in regulation of TLR-2, TLR-4, hBD-1 and cathelicidin release.     

Skin response to epicutaneous application of anticoagulant rodenticide warfarin is characterized by differential time- and dose-dependent changes in cell activity

Context: Skin is the target of both acute and chronic exposure to warfarin, coumarin anticoagulant. Single exposure of rat skin to this agent induces early (24?h following epicutaneous administration) local response which might be part of inflammatory/reparatory homeostatic program or introduction to pathological events in exposed skin.

Objective: To examine time-dependent changes in skin of rats exposed to epicutaneously applied warfarin.

Materials and methods: The effect of low (10?μg) and high (100?μg) doses of warfarin on histologically evident changes of epidermis (epidermal thickness) and dermis (numbers of mesenchymal cells and dermal capillaries), skin cell proliferative activity (Ki67⁺ and PCNA⁺ cells) and apoptotic (TUNEL⁺) and necrotic (ultra structural appearance) cells was examined one, three and seven days after the application.

Results: Both warfarin doses affected the majority of skin cell activity, but with differential time-course of skin epidermal and dermal cells state/activity. The occurrence of necrotic/apoptotic epidermal and dermal cells was noted the first day after the application and the activities which point to tissue reparation/remodeling were observed seven days after skin exposure to this agent.

Discussion: The observed pattern of changes (early evidence of cell/tissue injury which was later followed by signs of cell activity characteristic for tissue reparation/remodeling) implied warfarin-induced toxicity in skin cells as stimulus for subsequent activities relevant for tissue homeostasis.

Conclusion: The data presented provide new and additional information concerning skin responses to warfarin that gains access to this tissue.     

Structure/Effect Studies of Fatty Acid Isomers as Skin Penetration Enhancers and Skin Irritants

Comparisons were made of branched vs unbranched saturated fatty acids and cis vs trans unsaturated fatty acids as skin penetration enhancers and primary skin irritants. Skin penetration studies used naloxone base as the diffusant, propylene glycol as the vehicle, and human skin. Maximum naloxone flux was with C_9–12-branched and unbranched fatty acids. For C_5–14 fatty acids, branched and unbranched isomers had similar effects. One branched C₁₈ fatty acid isomer (C₁₆-branched isostearic acid) was more effective in enhancing skin penetration than a differently branched (C₂-branched isostearic acid) or unbranched C₁₈ isomer (stearic acid). There was no significant difference between cis and trans unsaturated C_16–18 fatty acid isomers in their effects on naloxone flux, and all unsaturated fatty acids were more effective enhancers than the corresponding saturated isomers. Several of these fatty acid/propylene glycol vehicles were evaluated in a rabbit primary skin irritation test. Irritation indices were poorly correlated with the effectiveness of the vehicles in enhancing naloxone flux. It was possible to enhance naloxone skin penetration greatly with a vehicle with only minimal skin irritation potential.     

Characterization of dry skin associating with type 2 diabetes mellitus using a KK-Ay/TaJcl mouse model

Purpose: Type 2 diabetes mellitus (DM) induces various dermatological conditions that can affect patient quality of life, including increased susceptibility to skin infections and dry skin. While the mechanisms that underlie the causes of dry skin in type 1?DM have been widely studied, how type 2?DM elicits similar effects is unclear. The purpose of this study was therefore to evaluate skin barrier and hydration function using a KK-A^y/TaJcl mouse model of type 2?DM.

Materials and methods: KK-A^y/TaJcl and control mice were housed separately for 4 weeks and then body weight, water intake, urine production, and blood glucose levels were measured. Skin barrier function was estimated by assessing transepidermal water loss (TEWL) and hydration levels of the stratum corneum. The expression levels of various skin biochemical factors were also examined by western blot, including type 1 collagen, mast cell tryptase, hyaluronic acid binding protein (HABP), and fibroblast protein S100A4.

Results: Compared to control mice, there was a marked increase in body weight, water intake, urine production, and blood glucose levels in the KK-A^y/TaJcl mice over the length of the experiment. Hydration levels in the stratum corneum were lower in KK-A^y/TaJcl mice compared to control mice, although TEWL was not significantly different between groups. We also found that hyaluronic acid binding protein expression was higher in KK-A^y/TaJcl mice, although other biochemical factors were the same.

Conclusions: These findings suggest that hyaluronic acid associates with the dry skin caused by type 2?DM. This contributes to understanding this phenomenon and may lead to better treatment options for patients in the future.     

Transport of β-Estradiol in Freshly Excised Human Skin in Vitro: Diffusion and Metabolism in Each Skin Layer

This paper describes an experimental and theoretical evaluation of -estradiol (E2) transport in post-surgery fresh human skin in vitro. Necessary auxiliary experimental methods were newly developed for these studies. The experimental fluxes of E2 and the metabolite, estrone (El), using the dermis, stripped skin, and split-thickness skin were consistent with a model considering the human skin as a three-layer (stratum corneum, viable epidermis, and dermis) membrane with the enzyme activity mainly residing in the basal layer of the viable epidermis. The diffusion and metabolism parameters for each skin layer were determined in the overall transdermal transport of E2. Compared to fresh hairless mouse skin, fresh human skin appears more resistant to the stratum corneum diffusion of E2 and is much less capable of metabolizing E2 to El. These in vitro results have been extrapolated to the possible in vivo human skin situation with blood vessels directly beneath the viable epidermis providing sink conditions a short distance from the dermo-epidermal junction. The model analysis has demonstrated that there would be less metabolism and that a much smaller amount of the transdermal metabolite (El) would be taken up by the blood capillary due to the shorter dermis path length for permeants in vivo than in the in vitro case using dermatomed split-thickness skin.     

Employing photoacoustic spectroscopy in the evaluation of the skin permeation profile of emulsion containing antioxidant phenolic-rich extract of Melochia arenosa

Context: Oxidative stress is an important factor modulating skin alterations. Melochia arenosa Benth. (Malvaceae) is a Brazilian plant with antimicrobial activity and antioxidant potential.

Objective: The objective of this study is to develop a topical formulation containing antioxidant phenolic-rich extract of M. arenosa and to evaluate its skin permeation profile.

Materials and methods: Response surface methodology was used to maximize the total phenolic (TP) content of the extract and its antioxidant activity was evaluated by 2,2-diphenyl-1-picryl-hydrazyl (DPPH), 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and respiratory burst methods. An emulsion containing 1% optimized extract (OE) was developed and employed photoacoustic spectroscopy (PAS) for the determination of its skin permeation profile. The morphology of the skin was studied in histological sections stained with hematoxylin–eosin.

Results and discussion: The optimum conditions predicted for the major extractive efficiency of the phenolics with 100% ethanol led extraction time 101?h and plant:solvent proportion 1:13.5 (w/v). OE presented TP?=?724.6?±?8.2?mg GAE/g extract and scavenging capacity of DPPH (IC₅₀ value?=?11.43?±?0.14?µg/mL) and ABTS radicals (IC₅₀ value?=?35.42?±?0.48?µg/mL). The production of ROS by neutrophils after stimulation with phorbol miristate acetate was lower when the OE was present in the reaction medium, endorsing its high antioxidant capacity. The data obtained by PAS indicated that the OE present in the emulsion has permeated and was distributed in the whole skin. No histopathological alterations were observed in the histological analysis.

Conclusion: The formulation developed is a promising tool for skin care and could prevent the damage caused by oxidative stress.     

Topical delivery of acyclovir and ketoconazole

Abstract

Context: Viral and fungal cutaneous manifestations are regularly encountered in immunocompromised human immunodeficiency virus/acquired immunodeficiency syndrome individuals and can be treated by drugs such as acyclovir and ketoconazole, respectively.

Objective: The aim of this study was to determine whether the novel Pheroid? delivery system improved the transdermal delivery and/or dermal delivery of acyclovir and ketoconazole when incorporated into semi-solid formulations.

Materials and methods: Semi-solid products (creams and emulgels) containing these drug compounds were formulated, either with or without (control) the Pheroid? delivery system. The stability of the formulated semi-solid products was examined over a period of six months and included the assay of the actives, pH, viscosity, mass loss and particle size observation. Vertical Franz cell diffusion studies and tape stripping methods were used to determine the in vitro, stratum corneum (SC)-epidermis and epidermis-dermis delivery of these formulations.

Results and discussion: Stability tests showed that none of the formulations were completely stable. Acyclovir showed a biphasic character during the in vitro skin diffusion studies for all the tested formulations. The Pheroid? cream enhanced the transdermal, SC-epidermis and epidermis–dermis delivery of acyclovir the most. The average amount of ketoconazole diffused over 12?h showed improved delivery of ketoconazole, with the Pheroid? emulgel exhibiting the best transdermal and epidermis–dermis delivery.

Conclusion: The Pheroid? formulae increased transdermal penetration as well as delivery to the dermal and epidermal skin layers. The Pheroid? emulgel and the Pheroid? cream increased the topical delivery of ketoconazole and acyclovir, respectively.     

Design of solid lipid nanoparticles for caffeine topical administration

Context: Solid lipid nanoparticles (SLN) are drug carriers possessing numerous features useful for topical application. A copious scientific literature outlined their ability as potential delivery systems for lipophilic drugs, while the entrapment of a hydrophilic drug inside the hydrophobic matrix of SLN is often difficult to obtain.

Objective: To develop SLN intended for loading caffeine (SLN-CAF) and to evaluate the permeation profile of this substance through the skin once released from the lipid nanocarriers. Caffeine is an interesting compound showing anticancer and protective effects upon topical administration, although its penetration through the skin is compromised by its hydrophilicity.

Materials and methods: SLN-CAF were formulated by using a modification of the quasi-emulsion solvent diffusion technique (QESD) and characterized by PCS and DSC analyses. In vitro percutaneous absorption studies were effected using excised human skin membranes (i.e. Stratum Corneum Epidermis or SCE).

Results: SLN-CAF were in a nanometric range (182.6?±?8.4?nm) and showed an interesting payload value (75%?±?1.1). DSC studies suggest the presence of a well-defined system and the successful drug incorporation. Furthermore, SLN-CAF generated a significantly faster permeation than a control formulation over 24?h of monitoring.

Discussion and conclusions: SLN-CAF were characterized by valid dimensions and a good encapsulation efficiency, although the active to incorporate showed a hydrophilic character. This result confirms the suitability of the formulation strategy employed in the present work. Furthermore, the in vitro evidence outline the key role of lipid nanoparticles in enhancing caffeine permeation through the skin.