Bioavailability of topically administered steroids: a "mass balance" technique

In vitro percutaneous penetration test overview

Skin is a detailed, organized, and intricate niche in the human body. Topical and transdermal drugs are unique, in that their absorption is quite different from other routes of administration (oral, intramuscular, intravenous, etc.,.). A robust amount of research is required to approve the use of a drug-in vivo, in vitro, and ex vivo studies collectively help manufacturers and government agencies with approval of various compounds. Use of human and animal studies poses ethical and financial concerns, making samples difficult to use. In vitro and ex vivo methods have improved over the past several decades-results show relevance when compared to in vivo methods. The history of testing is discussed, followed by a detailed account of known complexities of skin and the current state of percutaneous penetration.

Development of human dermal PBPK models for the bisphenols BPA, BPS, BPF, and BPAF with parallel-layered skin compartment: Basing on dermal administration studies in humans

Risk assessment of human exposure to bisphenols (BPs) including bisphenol A, S, F and AF (BPA, BPS, BPF and BPAF) have suggested that except for ingestion, health risk resulting from dermal contact is not negligible. However, the absorption kinetics of BPA substitutes in humans following dermal exposure have been poorly studied. This study aimed to address the knowledge gap in physiologically based pharmacokinetic (PBPK) modeling of BPA and its high-concerned substitutes (BPS, BPF and BPAF) following dermal administration. Parallel-layered skin compartmental model for dermal absorption of BPs was for the first time proposed and human dermal administration studies were conducted to determine dermal bio-accessibility of BPS from thermal paper (TP) (n = 4), BPF (n = 4) and BPAF (n = 5) from personal care products (PCPs). Further, pharmacokinetics of BPS and its metabolites following human handling TP were investigated and the dermal PBPK models for BPA and BPS were validated using the available human biomonitoring data. Overall, 28.03 % ± 13.76 % of BPS in TP was transferred to fingers followed by absorption of 96.17 % ± 2.78 % of that. The dermal bio-accessibilities of BPs in PCPs were 31.65 % ± 2.90 % for BPF and 12.49 % ± 1.66 % for BPAF. Monte Carlo analysis indicated that 90 % of the predicted variability fell within one order of magnitude, which suggested that the developed PBPK models had medium uncertainty. Global sensitivity analysis revealed that the model uncertainty is mainly attributed to the variabilities of dermal absorption parameters. Compared with the previous models for BPs, the developed dermal PBPK models were capable of more accurate predictions of the internal dose metric in target organs following human dermal exposure to BPs via TP and PCPs routes. These results suggested that the developed human dermal PBPK models would provide an alternative tool for assessing the risk of human exposure to BPs through dermal absorption.

Effect of soak and smear on [14C]-hydrocortisone in vitro human skin percutaneous penetration

INTRODUCTION

'Soak and smear' method, water soaking to induce skin hydration followed by topical corticoids application suggests effectiveness in clinical dermatological practice. We investigate one possible mechanism of soaking times effect on drug partitioning and diffusion rates in skin and its proposed efficacy.

METHODS

Utilizing an in vitro flow-through diffusion system to evaluate efficacy of the 'soak and smear' method following 0.5, 8, and 20 min water soaking and [¹⁴C]-hydrocortisone topical application on human skin to probe the possibility of percutaneous penetration enhancement.

RESULTS

In water-soak groups, more [¹⁴C]-hydrocortisone was absorbed and retained in stratum corneum and epidermis, whereas, in the control (no soak) more was in the deep skin-dermis and receptor fluid. These differences between water-soak groups and the control are statistically significant (p < .05).

CONCLUSION

Effect of 'soak and smear' on skin absorption and penetration depends on interaction of individual drug's physicochemical property, stratum corneum hydration, and stratum corneum-epidermoid barrier status. Water soaking (≤ 20 min) induced skin hydration increases [¹⁴C]-hydrocortisone absorption and retention into the upper skin layer but not deep layers. This could support the proposed hypothesis of clinical dermatological treatment of hydrocortisone to local skin inflammations should the epidermis be found to be a key target for atopic dermatitis therapy.

Effect of superabsorbent polymers (SAP) and metal organic frameworks (MOF) wiping sandwich patch on human skin decontamination and detoxification in vitro

Most chemical warfare agents partition rapidly into stratum corneum (SC) and subsequently slowly diffuse through - or are retained in the membrane. Since chemicals can interact with SC components during the process, skin decontamination poses a challenging yet important problem. To address these issues, we have developed a new method in combination with wet and dry decon technologies with new materials for emergency or delayed contamination scenarios. An in vitro human skin diffusion system was employed to model various dermal exposures of radiolabeled chemical warfare simulants, followed by surface decontamination with metal organic frameworks (MOFs), super-absorbent polymers (SAP), and/or dermal decontamination gel (DDGel). All samples measured for radioactive recovery and acetylcholinesterase activity to ascertain relative decon efficacy. Results demonstrated powerful water absorption of SAP, strong catalysis of UiO-66 MOF, and decon enhancement of pre-wetting surface contaminants. SAP had no interfering interactions with MOF yet provided additional benefits as porosity and reactivity that allowed for fast liquidized chemical transportation, absorption, and degeneration. We then designed a cotton-based SAP/MOF patch that worked cooperatively in decontamination and detoxification. Together with pre-wet, SAP/MOF wipe, and DDGel applications, maximum effect was observed in early and/or extended dermal exposure, and no "wash-in" effect occurred.

Measurement of the penetration of 56 cosmetic relevant chemicals into and through human skin using a standardized protocol

OECD test guideline 428 compliant protocol using human skin was used to test the penetration of 56 cosmetic‐relevant chemicals. The penetration of finite doses (10 μL/cm²) of chemicals was measured over 24 hours. The dermal delivery (DD) (amount in the epidermis, dermis and receptor fluid [RF]) ranged between 0.03 ± 0.02 and 72.61 ± 8.89 μg/cm². The DD of seven chemicals was comparable with in vivo values. The DD was mainly accounted for by the amount in the RF, although there were some exceptions, particularly of low DD chemicals. While there was some variability due to cell outliers and donor variation, the overall reproducibility was very good. As six chemicals had to be applied in 100% ethanol due to low aqueous solubility, we compared the penetration of four chemicals with similar physicochemical properties applied in ethanol and phosphate‐buffered saline. Of these, the DD of hydrocortisone was the same in both solvents, while the DD of propylparaben, geraniol and benzophenone was lower in ethanol. Some chemicals displayed an infinite dose kinetic profile; whereas, the cumulative absorption of others into the RF reflected the finite dosing profile, possibly due to chemical volatility, total absorption, chemical precipitation through vehicle evaporation or protein binding (or a combination of these). These investigations provide a substantial and consistent set of skin penetration data that can help improve the understanding of skin penetration, as well as improve the prediction capacity of in silico skin penetration models.

The penetration of 56 chemicals was tested in human skin using a standard protocol. Dermal delivery correlated with the amount in the receptor fluid (RF). The impact of solvent on penetration was evaluated. Despite finite doses being applied, different profiles of cumulative absorption kinetics into the RF were observed. These data may help understand skin penetration and improve the prediction capacity of in silico skin penetration models.

Acute dermal toxicity study of new, used and laboratory aged aircraft engine oils

There is little data available on toxicity levels of used aircraft engine oils relative to their unused (new) versions. This study was conducted to determine if new engine oils and their used versions have the potential to induce dermal irritation. Twelve male New Zealand White rabbits (Oryctolagus cuniculus, 19 weeks old) were used to determine the acute dermal toxicity potential of four aircraft turbine oils including MIL-PRF-7808 Grades 3 and 4 and MIL-PRF-23699 Grade 5 High Thermal Stability (HTS) and a Grade 5 experimental aircraft engine oil in their unused and used or laboratory stressed states. Five fur-free test sites (6 cm² each) located lateral to the midline of the back were treated with two undiluted (0.5 ml) new engine oils and their used versions. The fifth site received reverse osmosis deionized (RODI) water as a control. Each treatment was repeated 3 times (3 rabbits/oil type). Each oil was tested under both semi-occluded and occluded conditions. The 4 h exposure was followed by gauze plus wrappings removal, and gentle cleaning of sites prior to scoring for erythema and edema at 0.5-1, 24, 48 and 72 h post exposure based on Draize (1959). E-collars were placed on each animal for at least 72 h to prevent ingestion of the test substance and/or gauze and wrappings and/or disturbance of site recovery. Additional observations were made on days 7, 10 and 14 to determine recovery. Exposure to both used and new oils produced dermal irritation consisting of no more than very slight to well-defined erythema and very slight edema. The calculated Primary Dermal Irritation Index (PDII) indicated that all the oils were slightly irritating (means ranged from 0.42 to 1.08). Although the PDII values for new oils and their used versions were not significantly different from each other, they were all statistically higher (p < 0.05) than those obtained for the control regardless of the type of occlusion binding applied. The used oils under semi-occlusion conditions yielded larger size effects (Cohen's d) relative to their unused versions suggesting an enhancement in irritation when the oil is aging. Grade 4 in the used state yielded the largest size effect which was d = 5.9 versus 2.6 for its unused version. The slight dermal irritation resulting from four hours of exposure to oils raises concerns about the magnitude of impact related to prolonged and/or repeated exposure.

Use of a Simple in vitro Test to Assess Loss of Chemical due to Volatility during an in vitro Human Skin Absorption Study

BACKGROUND

We tested the cutaneous distribution of 50 chemicals in frozen human skin. The mass balance (MB) values for 48% of the chemicals were < 90%, possibly due to evaporation.

METHODS

We confirmed the reduction in MB was due to evaporation for two chemicals tested in skin penetration experiments using a carbon filter above the skin to trap airborne chemical. An in vitro assay was used to predict the reduction in MB due to evaporation by comparing the recovery of chemicals after 4 h of incubation at room temperature in open and closed vials.

RESULTS

Evaporative losses in vitro correlated well with measured MBs (i.e., < 90%) in skin penetration experiments (R2 = 0.81). There was a correlation of the MB with the vapour pressure (VP) which could be used to group chemicals according to their likelihood to evaporate during the course of a skin penetration study. There was also a correlation of MB with Henry's law constants, melting and boiling points.

CONCLUSION

Our data support the use of a quick and simple test for volatility to account for the loss of MB in skin penetration experiment due to volatility. The best parameter to indicate the potential of a chemical to evaporate is the VP.

Is the Skin Absorption of Hydrocortisone Modified by the Variability in Dosing Topical Products?

Fingertip units have been proposed as a tool to standardize topical therapy with semisolid formulations. However, no studies to date have characterized the variability in dosing by patients using this concept and whether this variability ultimately affects the topical absorption of drugs. This work aimed to answer these two questions. A first study determined the dose measured, the area of spread and the area-normalized dose for a 1% hydrocortisone cream and ointment applied by members of the public using this dosing approach before and after brief counselling. Then, in vivo tape-stripping and in vitro permeation studies investigated whether the variability in the area-normalized dose altered the skin absorption of hydrocortisone. Participants applied greater doses and spread them over larger areas after a short counselling intervention leading to smaller area-normalized doses. In vivo hydrocortisone uptake by the stratum corneum was significantly greater for the higher normalized dose and the differences were further supported by the in vitro permeation studies. However, these differences were relatively small and not proportional to the increase in normalized dose. This work shows that, following brief advice, patients and carers can apply consistent and sufficient doses of corticosteroids whilst minimizing risks and variability in hydrocortisone absorption.

Mechanistic Evaluation of Hydration Effects on the Human Epidermal Permeation of Salicylate Esters

We sought to understand when and how hydration enhances the percutaneous absorption of salicylate esters. Human epidermal membrane fluxes and stratum corneum solubilities of neat and diluted solutions of three esters were determined under hydrated and dehydrated conditions. Hydration doubled the human epidermal flux seen for methyl and ethyl salicylate under dehydrated conditions and increased the flux of neat glycol salicylate 10-fold. Mechanistic analyses showed that this hydration-induced enhancement arises mainly from an increase in the stratum corneum diffusivity of the three esters. Further, we showed that unlike methyl and ethyl salicylate, glycol salicylate is hygroscopic and the ∼10-fold hydration-induced flux enhancement seen with neat glycol salicylate may be due to its ability to hydrate the stratum corneum to a greater extent. The hydration-induced enhancements in in vitro epidermal flux seen here for glycol and ethyl salicylate were similar to those reported for their percutaneous absorption rates in a comparable in vivo study, whilst somewhat higher enhancement was seen for methyl salicylate in vivo. This may be explained by a physiologically induced self enhancement of neat methyl salicylate absorption in vivo which is not applicable in vitro.

Transdermal delivery of testosterone

Male hypogonadism has been treated with exogenous testosterone since the 1930s. The early transdermal patches of testosterone became available in the 1980s with gel and solution preparations following subsequent decades. This review focusses on the skin permeation characteristics of testosterone, pharmacokinetics following application of transdermal formulations and formulations currently available. At present, gels dominate the market for transdermal testosterone replacement therapy, presumably because of their greater patient acceptability and non-occlusive nature compared with patches. However, specific incidences of secondary transfer of gels to children with consequent unwanted effects such as precocious puberty have been reported. A regulatory review of all testosterone replacement therapies is currently underway which may have implications for future prescribing practices of transdermal testosterone products.

Comparison of reservoir effect of topical corticosteroids in an experimental animal model by histamine-induced wheal suppression test

Introduction:

Topical corticosteroids used in various dermatological diseases are available in different potencies and different formulations. The reservoir effect of different potency corticosteroids in the stratum corneum will help the clinicians to choose an appropriate topical steroid to maximize their efficacy and safety as therapeutic agents.

Aims:

This study was designed to compare the duration of reservoir of different potency topical corticosteroids experimentally in rabbits using histamine-induced wheal suppression test.

Materials and Methods:

The study was carried out in albino rabbits (as their skin is similar to humans) using four different concentrations of topical steroids, namely mometasone furoate ointment (0.1%), fluticasone propionate ointment (0.005%), betamethasone valerate cream (0.1%), and hydrocortisone butyrate cream (0.1%). These were applied on the back of rabbit on one side and the vehicle was applied on the other. One hour later, histamine-induced wheal suppression test was performed on both sides and wheal area was measured at 10 min for 7 days. Statistical analysis was done by ANOVA followed by post hoc test.

Results:

Maximum wheal suppression was seen on day 1 (P<0.001) in all four groups, both at test and at control sites. Interday comparison of mean wheal size by topical steroids showed that the reservoir of mometasone furoate ointment (0.1%) persisted till day 4 in the stratum corneum of the skin. In case of fluticasone propionate ointment (0.005%) and betamethasone valerate cream (0.1%), the reservoir persisted till day 2 and for hydrocortisone butyrate cream (0.1%), the reservoir was present only on day 1.

Conclusions:

It is concluded that the duration of reservoir depends on the potency of topical steroids. Higher the potency more is the duration of reservoir in stratum corneum and vice versa.

Study of reservoir effect of clobetasol propionate cream in an experimental animal model using histamine-induced wheal suppression test

BACKGROUND

Topical corticosteroids used in various dermatological diseases several times a day led to an increase risk of side effects. By demonstrating a significant reservoir of corticosteroids in the stratum corneum, one can maximize their efficacy and safety as therapeutic agents.

AIM

The study was designed to demonstrate a reservoir of topically applied corticosteroid clobetasol propionate cream experimentally in rabbits using histamine-induced wheal suppression test.

MATERIALS AND METHODS

The work was carried out on albino rabbits, as rabbit skin is akin to human skin, using a topical steroid. The topical steroid clobetasol propionate 0.05% cream was applied on the back of rabbit, and after 1-h occlusion histamine-induced wheal suppression test was performed and wheal area measured at 10 min till day 7. Statistical analysis was done by ANOVA followed by "Post Hoc" test.

RESULTS

Maximum wheal suppression was seen on day 1 (P < 0.001). Interday comparison of mean wheal size showed no significant difference (P > 0.05) on day 2, 3, and 4 as compared to day 1. Day 5-7 show highly significant difference (P < 0.001) as compared to day 1, thereby suggesting that the reservoir effect of topical clobetasol propionate 0.05% cream persisted till day 4.

CONCLUSIONS

This work demonstrated that histamine-induced wheal by the topical steroid clobetasol propionate 0.05% cream was suppressed till day 4, indicating that the reservoir of topical corticosteroid persisted till day 4.

Percutaneous absorption in man: in vitro-in vivo correlation

AIMS

To examine the existing literature to determine the degree to which percutaneous absorption data obtained using the excised human skin model match those obtained from living man.

METHODS

The scientific literature was reviewed to collect data on compounds whose percutaneous absorption through human skin had been measured under both in vitro and in vivo conditions. The in vitro-in vivo (IVIV) correlation was evaluated by computing the in vitro/in vivo ratio using total absorption (percent of applied dose) as the metric for comparison.

RESULTS

A total of 92 data sets were collected from 30 published studies. The average IVIV ratio across all values was 1.6, though for any single data set there could be a nearly 20-fold difference between the in vitro and in vivo values. In 85% of the cases, however, the difference was less than 3-fold. The correlation was significantly improved when data were excluded from studies in which the protocols for both studies were not fully harmonized. For harmonized data sets the average IVIV ratio was 0.96 and there was a less than 2-fold difference between the in vitro and in vivo results for any one compound, with IVIV ratios ranging from 0.58 to 1.28. The dominant factors leading to exclusion of data were the use of skin from different anatomical sites and vehicles of differing composition.

CONCLUSIONS

Percutaneous absorption data obtained from the excised human skin model closely approximate those obtained from living man when the two study protocols are appropriately matched.

Percutaneous absorption and exposure assessment of pesticides

Dermal exposure to a diverse range of chemicals may result from various uses. In order to assess exposure and estimate potential risks, accurate quantitative data on absorption are required. Various factors will influence the final results and interpretations of studies designed to assess the ability of compounds to penetrate the skin. This overview will discuss skin penetration by pesticides, emphasizing key parameters to be considered from the perspective of exposure assessment.

An open‐label pilot study to evaluate the safety and efficacy of topically applied tacrolimus ointment for the treatment of hand and/or foot eczema

BACKGROUND

Hand and foot eczema is a chronic skin disorder. Although topical corticosteroids are often used to control the predominant symptoms of the disease, the chronicity of the condition increases the risk of long-term adverse effects. A safer alternative is needed.

OBJECTIVE

To evaluate the safety and efficacy of tacrolimus ointment 0.1% in hand and/or foot eczema.

METHODS

Twenty-five adults applied tacrolimus ointment 0.1% to affected areas three times daily for 8 weeks and were followed for 2 additional weeks.

RESULTS

Except for vesiculation, compared with baseline there were significant improvements in erythema, scaling, induration, fissuring, composite severity, and pruritus (p<0.007). Two weeks after discontinuing treatment, significant improvement in scaling and composite severity (p<0.03) persisted, whereas erythema, induration, vesiculation, fissuring, and pruritus had returned to pre-treatment levels.

CONCLUSION

Tacrolimus ointment 0.1% is a promising corticosteroid alternative for hand/foot eczema.

Enhancement of skin permeation of docetaxel: a novel approach combining microneedle and elastic liposomes

A combination method of using microneedle pretreatment and elastic liposomes was developed to increase skin permeation of drugs with high molecular weight and poor water solubility. Docetaxel (DTX, MW=807.9) was chosen as a model drug. DTX liposomal systems with and without elastic properties were prepared and characterized. The effect of the developed formulations on the permeation of DTX across both rat and porcine skin was investigated in vitro. The combination effect of microneedle pretreatment and elastic liposomes on the permeability of DTX was evaluated using porcine skin in vitro. The following results were obtained: (1) Elastic liposomes loaded with DTX can enhance transdermal delivery of DTX without microneedle treatment. (2) An enhanced transdermal flux (1.3-1.4 microg/cm(2)/h) for DTX from all liposomal formulations was observed after microneedle treatment. Importantly, the lag time obtained following the application of elastic liposomes through microneedle-treated skin was decreased by nearly 70% compared with that obtained from conventional liposomes. These results suggest that the combination of elastic liposomes with microneedle pretreatment can be a useful method to increase skin permeation of drugs with high molecular weight and poor water solubility.

Development and characterization of film forming polymeric solutions for skin drug delivery

Film forming polymeric solutions as a novel approach for skin drug delivery were developed and characterized concerning their mechanical properties and water vapor permeability. They were developed by varying type and content of the film forming polymer as well as nature and content of the plasticizer. The resulting formulations were evaluated according to five criteria: drying time, cosmetic attractiveness, outward stickiness, integrity on skin (after 18 h) and viscosity. Among the 14 tested polymers 10 film formers yielded formulations with a positive evaluation in all five test criteria. Selected formulations were then investigated for tensile strength and elongation at break in vitro and for water vapor permeability in vitro (WVP) and in vivo (TEWL). Their mechanical properties determined in vitro were found to be not predictive for the flexibility and abrasion resistance observed on living skin. Similar to this, the results derived from the WVP and the TEWL methods were not in accordance with each other. Obviously, the investigated in vitro methods do not characterize the properties of the thin films on living skin satisfactorily. Nevertheless, the identified film forming solutions are a promising approach and will provide the basis for the further development of this novel dosage form.

Topical Bioavailability of Triamcinolone Acetonide: Effect of Occlusion

BACKGROUND/AIMS

Occlusion by covering the skin with an impermeable wrap enhances skin hydration, affects drug absorption and can induce the formation of a drug reservoir within the stratum corneum. This is desired in local therapy with topical corticosteroids. The aim of the study was to investigate the effect of occlusion before (experiment 1) and after (experiment 2) application on the penetration of triamcinolone acetonide (TACA) into the stratum corneum.

METHODS

The experiments were conducted on the forearms of 10 healthy volunteers. In experiment 1, 100 microg/cm(2) TACA in acetone were applied on 3 sites per arm, one arm having been pre-occluded for 16 h. In experiment 2, the same dose was applied on 2 sites per arm, and one arm was occluded after application until skin sampling. Stratum corneum samples were removed by tape stripping at 0.5, 4 and 24 h (experiment 1) and 4 and 24 h (experiment 2) after application. Corneocytes and TACA were quantified by ultraviolet-visible spectroscopy and HPLC, respectively. The total TACA amount penetrated into the stratum corneum was evaluated by multifactor ANOVA.

RESULTS

TACA penetration into the stratum corneum with and without pre-occlusion (experiment 1) showed no significant difference and decreased with time. Occlusion after application (experiment 2) produced a marked TACA accumulation within the stratum corneum, which persisted for 24 h.

CONCLUSION

Pre-occlusion showed no effect on the topical bioavailability of TACA in the stratum corneum. In contrast, post-occlusion enhanced the TACA penetration by a factor of 2, favouring the development of a drug reservoir.

Skin changes induced by a zinc oxide dressing compared with a hydrocolloid dressing in healthy individuals

BACKGROUND/PURPOSE

Incidence of skin complications in ostomy patients constitutes a well-known and well-described problem. The reasons are, however, very difficult to describe because of the many factors contributing to the problem. This article describes the skin changes derived exclusively from the adhesives used in a carefully controlled, long-term study using two fundamentally different types of adhesives: a hydrocolloid adhesive and a zinc oxide adhesive.

METHODS

The adhesives were changed daily on the volar forearm of 11 volunteers for a 4-week period. Once a week, transepidermal water-loss (TEWL), water content of the skin, erythema and the peel force applied for removal of the adhesives were measured. On the last day of the study, a replica of the skin surface was obtained to determine changes in the skin topography, and a biopsy was taken to study changes at the cellular level.

RESULTS AND CONCLUSION

We found increased TEWL and decreased water content in skin treated with the zinc oxide adhesive, but increased water-loss and water content when the hydrocolloid adhesive was used. In addition, the area treated with zinc oxide adhesive showed significant increase of epidermal thickness, scaly appearance and parakeratosis with similarities to pathological dry skin diseases such as psoriasis and atopic dermatitis, changes that were not found when using the hydrocolloid adhesive. The skin response seems to be the result of the content of zinc oxide and the mechanical interaction of the zinc oxide adhesive. We conclude that the nature of the adhesive plays an important role in the skin response to repeated application of adhesives, as seen in peristomal skin.

Percutaneous absorption of Mexoryl SX in human volunteers: comparison with in vitro data

The potential human health risk of UV filters depends on their toxicity and the human systemic exposure which is a function of the extent of percutaneous absorption of the topically applied substance into the human organism. Using a 'mass balance' approach, a study was designed to investigate the systemically absorbed dose of [(14)C]-Mexoryl SX((R)) in humans after topical application of a typical sunscreen emulsion. In addition, to assess the correlation with in vitro experiments, the percutaneous absorption of this UVA filter through isolated human skin was measured under identical exposure conditions. When applied in vivo for a period of 4 h, 89-94% of the applied radioactivity was recovered from the wash-off samples. In urine samples, the radioactivity slightly exceeded background levels and corresponded maximally to 0.014% of the topically applied dose. No radioactivity was measured in blood or faeces sampled up to 120 h after application. In vitro, 24 h after a 4-hour application, [(14)C]-Mexoryl SX remained primarily on the skin surface. The mean in vitro absorption over 24 h, adding up the amounts found in the dermis and receptor fluid, was 0.16% of the applied dose. It is concluded from the in vivo pharmacokinetic results that the systemically absorbed dose of [(14)C]-Mexoryl SX is less than 0.1%. The order of magnitude of this value correlates well with the corresponding in vitro data which overestimate the in vivo results as previously observed with other hydrophilic compounds. This study demonstrates that, under realistic exposure conditions, the human systemic exposure to this UVA filter is negligible and poses no risk to human health.

Development of an in vivo animal model for skin penetration in hairless rats assessed by mass balance

The aim of the study was to develop an in vivo animal model for studies of the penetration of topically applied drugs into the skin of hairless rats. Protective appliances were designed for non-occluded and finite-dose application of topical formulations. The design allowed 2 test sites for each rat and free mobility throughout the test period. By consecutive tape stripping, monitored by measurements of transepidermal water loss and confirmed by histological examination of skin biopsies, 10 tape strippings were found to remove the stratum corneum completely. For assessment of the model, (14)C-salicylic acid and (14)C-butyl salicylate were topically applied. Rapid and differentiated percutaneous absorption of both compounds were shown by urinary excretion data. For (14)C-salicylic acid the amount on the skin surface, in the stratum corneum and in the viable skin was determined. Total mass balance on the applied radioactivity was performed and a recovery of 90 +/- 2% was achieved. The radioactivity found in the protective appliances (<10%) was explained by lateral skin diffusion of the model compounds into the dressings.

Physiological changes in skin barrier function in relation to occlusion level, exposure time and climatic conditions

Skin occlusion is a condition encountered with various articles as part of everyday life and resulting changes in skin barrier physiology often remain unnoticed. In the present study we aimed to understand the impact of absorbent feminine hygiene articles, one vapor-permeable and one vapor-impermeable, on skin hydration in response to exposure time and different environmental climatic conditions. Using a forearm model, volunteers were patched with moistened vapor-permeable and -impermeable articles in parallel for 1, 3, and 6 h and under different climatic conditions (i.e. 20 degrees C/30% relative humidity, 25 degrees C/50% relative humidity, 30 degrees C/ 75% relative humidity). The physiological changes in the skin barrier function were measured via skin hydration, evaporation of superficial water (skin surface water loss, SSWL) and relative humidity in the microclimate between skin and occlusive article (RH(mc)). The results show that skin hydration, SSWL, and RH(mc) under a vapor-permeable article are reduced versus the vapor-impermeable article for all exposure times at 25 degrees C and 50% relative humidity. SSWL and RH(mc) decrease from their 1-hour peak values with increasing exposure time, while skin hydration decreases only after 3 h of exposure. Lower environmental temperature (20 degrees C) and lower relative humidity (30%) have little impact on the reduction of SSWL and RH(mc,) but more so on the reduction of skin hydration. Higher temperature (30 degrees C) and higher relative humidity (75%) increase RH(mc) and skin hydration under both vapor-permeable and -impermeable articles while SSWL is reduced under the vapor-impermeable article under these conditions. In conclusion, vapor-permeability is the key factor for physiological changes in the barrier function of the skin under occlusion, exposure time and climatic conditions being modulating factors. These findings have been integrated into a model of skin hydration under occlusion in the context of absorbent hygiene articles. While current vapor-impermeable articles are effective in reducing the excessive moisture on the skin due to bodily discharge, vapor permeability adds a further measurable benefit in reducing skin overhydration.

Skin occlusion and irritant and allergic contact dermatitis: an overview

Occlusion, widely used to enhance percutaneous absorption of drugs, also increases penetration of other chemicals and antigens, and hence may exacerbate irritant and allergic contact dermatitis. This overview summarizes the adverse effects of occlusion.

Effects of skin occlusion on percutaneous absorption: an overview

Skin occlusion produces profound changes, including hydration status, barrier permeability, epidermal lipids, DNA synthesis, microbial flora, and numerous molecular and cellular processes. It often, but not always, increases percutaneous absorption of applied chemicals. This overview focuses on the effect of skin occlusion on percutaneous absorption.

The effect of occlusion on epidermal penetration of parabens from a commercial allergy test ointment, acetone and ethanol vehicles

The efficacy of topical allergy screening systems relies on the ability of test agents to effectively penetrate the stratum corneum from applied vehicles and reach the viable cells involved in the cutaneous immune response system. There is very little evidence in the dermatologic literature to justify the choice and suitability of vehicles used in many allergy test systems and the effectiveness of occlusion, reported to have variable effects on solute penetration, often employed in combination with these systems. In this study we evaluated the in vitro human epidermal penetration of a mixture of paraben ester preservatives from a commercially available test ointment and two commonly employed solvent vehicles (acetone and ethanol), together with the effect of occlusion on the rate of delivery from these systems. Parabens were applied as finite doses (5 mg per cm2) to epidermal membranes mounted in horizontal Franz-type diffusion cells. At intervals of 2 h for a total of 10 h the receptor phase (20% ethanol in distilled water) was completely removed and replaced. Occlusion was effected by the placement of a piece of high density polyethylene (20 microm) over the application site immediately after dosing. Concentrations of parabens in receptor fluid and remaining in the epidermis at the end of the study were determined by high-performance liquid chromatography. There was a significant change in the epidermal flux of parabens from each of the vehicles following occlusion. Whereas increases were observed for the acetone and ethanol vehicles a decrease was seen following occlusion of the ointment formulation. Changes in flux appeared to result from a significant decrease in the epidermal partitioning of the esters following occlusion of the ointment and primarily by an increase in paraben epidermal diffusivity (estimated from changes in flux/retention) following occlusion of the solvent vehicles. These studies show that the effects of occlusion are strongly vehicle dependent, having wide implications for optimization of this technique with a range of topically applied solutes.

Surface recovery and stripping methods to quantify percutaneous absorption of caffeine in humans

The percutaneous absorption of caffeine from two vehicles, an emulsion and an acetone solution, was quantified by in vivo techniques in humans. A surface recovery technique over a 6-h application and a stripping method after a 30-min application were performed on the volar aspect of the forearm on 12 volunteers. Caffeine was assessed by HPLC. Two phases were distinguished in the percutaneous absorption of caffeine: a higher filling up of the stratum corneum with the oil-in-water emulsion than with the acetone solution, which was then followed by a steady-state flux corresponding to the penetration in the living tissues. The permeability constants (Kp) with emulsion and acetone were 1.59 x 10(-4) and 9.53 x 10(-8) cm/h, respectively. The stripping method showed concentrations of caffeine in stratum corneum that were five times higher with emulsion (212 ng/cm2) than with acetone (37 ng/cm2). With acetone as a vehicle, approximately 40% of caffeine of the cornfield layer was found around the treated area. This sizeable lateral spread within the stratum corneum was not observed with the emulsion.

Double-blind controlled trial of progesterone vaginal cream treatment for cyclical mastodynia in women with benign breast disease

The clinical effectiveness and safety of vaginal micronized progesterone treatment in mastodynia were evaluated in a double-blind placebo controlled study. Eighty regularly menstruating women affected by severe cyclical mastodynia were randomly assigned to two groups of 40 patients. One group was treated for 6 cycles from the 19th to the 25th day of the cycle with 4 g of vaginal cream containing 2.5% natural progesterone. The other group was similarly treated with placebo. The treatment was preceded by a control cycle. All patients reported every day their breast pain on a 100 mm visual linear analogue scale (VAS). The response of breast tenderness and nodularity to treatment was assessed by clinical examination. Vaginal progesterone resulted significantly more efficacious than placebo in reducing mean ratings of breast pain on VAS and mean scores of breast tenderness to touch. Success of treatment, defined as reduction greater than 50% of basal mean score of breast pain on VAS, was achieved in the 64.9% of patients treated with progesterone and in the 22.2% of patients receiving placebo (p < 0.01). Conversely, at the end of treatment, the improvement in breast nodularity showed a not statistically significant difference between the two groups. No major side-effects were detected.

Effect of sodium lauryl sulfate-induced skin irritation on in vivo percutaneous penetration of four drugs

The influence of sodium lauryl sulfate-induced irritant contact dermatitis on in vivo percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment, 450 microliters saturated solutions of HC, IM, IB, or AC in isopropylmyristate were applied to the pretreated skin for 24 h. Systemic absorption was determined by urinary and fecal excretion of compounds. Drug concentrations in stratum corneum (obtained by tape cellophane stripping after decontamination of the application site) and in epidermis/dermis (punch biopsy) were also investigated. Systemic absorption of topically applied drugs (as evaluated by urinary and fecal excretion) in SLS-irritated skin was significantly increased for HC (factor 2.6) followed by IB (1.9 times) and IM (1.6 times) but not increased for AC. However, drug concentrations in the viable epidermis and dermis were 70% lower in SLS-irritated than normal skin for HC, but not different for IB, IM, and AC. Thus, the influence of the state of the skin (irritant dermatitis versus healthy) on percutaneous penetration was different for diverse drugs. The general assumption that percutaneous penetration and drug tissue concentrations were higher in diseased versus healthy skin was not found to be true in our irritated-skin model.

Effect of sodium lauryl sulfate-induced skin irritation on in vitro percutaneous absorption of four drugs

The influence of irritant contact dermatitis on percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated in vivo for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment animals were sacrificed. Percutaneous penetration was then measured using in vitro diffusion cells and the removed (pretreated) skin. The following parameters were determined: cumulative amount of compound penetrated, steady state flux, lag time, and permeability coefficient, skin concentration per unit area, and the relative amount of drug remaining in the skin (as a percentage of the cumulative amount of compound penetrated through the skin). SLS pretreatment resulted in moderate irritant dermatitis in all animals and increased in vivo transepidermal water loss 4.5 times. Flux was increased in SLS-pretreated skin as compared with controls for all four compounds, with the greatest enhancement for hydrocortisone (HC) (5.9 times), followed by indomethacin (IM) (4.6 times), ibuprofen (IB) (3.9 times), and acitretin (AC) (3.4 times). Skin concentrations increased to a smaller degree from 1.6 times (IB) and 2.6 times (HC) to 3.4 times (IM). However, AC skin concentrations were not different between the two groups. Thus, percutaneous penetration parameters were equivocally influenced by SLS-induced irritation. Increased skin concentrations were paralleled by even higher increases in flux.

Relation of application time to bioactivity of a potent topical glucocorticoid formulation

The vasoconstrictor assay in human beings was used to assess bioavailability during different time periods of exposure when 0.05% clobetasol propionate cream (Temovate) was applied and left on for periods of 0.5, 1.0, 1.5, and 16.0 hours and subsequently washed. Maximal responses were achieved by 1.5 hours of exposure, but there was no significant difference in intensity of vasoconstriction between 1.0, 1.5, and 16.0 hours of exposure before washing the sites. Exposures to 0.05% clobetasol propionate cream for 0.5 hour were not significantly different from 16-hour exposures to 0.05% fluocinonide cream, but exposures to 0.05% clobetasol propionate cream for 1.0, 1.5, and 16.0 hours all resulted in significant increases in vasoconstriction responses compared with fluocinonide cream applied and left on for 16 hours. Topical exposures to a superpotent topical steroid for a short time give vasoconstrictor responses equivalent to long time exposures.

In vivo percutaneous absorption of fragrance ingredients in rhesus monkeys and humans

The percutaneous absorption of the fragrance diethyl maleate was measured in vivo in human and monkey studies. With the application sites occluded, 54% of the applied dose of the volatile fragrance penetrated human skin in 24 hr compared with 69% absorption in the monkey skin. It was concluded that the monkey is a good model for human skin with regard to the penetration of this fragrance material since no significant difference in the absorption of diethyl maleate was observed. The percutaneous absorption of the fragrances benzyl acetate and five other benzyl derivatives (benzyl alcohol, benzyl benzoate, benzamide, benzoin and benzophenone) was determined in vivo in monkeys. Absorption through occluded skin was high for all compounds (approximately 70% of the applied dose in 24 hr) and no significant differences between the values for the different compounds were observed. No correlations were seen between skin penetration of these compounds and their octanol-water partition coefficients. Under unoccluded conditions skin penetration of the fragrances was reduced and there was great variability between compounds, presumably because of variations in the rates of evaporation from the site of application. The data suggest that humans may have significant systemic exposure to these fragrance materials.

The barrier function of the skin in relation to percutaneous absorption of drugs

There is currently a high level of interest in using the skin as a route for delivering drugs. The skin, however, provides an efficient barrier against percutaneous absorption of drugs. This barrier function can be ascribed to the macroscopical structure of the stratum corneum, which consists of alternating lipoidal and hydrophylic regions. For this reason, physico-chemical characteristics of the drug, such as partition coefficient and molecular weight, play an important role in determining the facility of percutaneous absorption. Another factor to consider in transdermal drug delivery, is the vehicle in which the drug is formulated as it acts on the release of drug from the formulation. Moreover, vehicles may also interact with human stratum corneum, thereby affecting its barrier function. Surfactants and penetration enhancers are well-known examples of the latter. Subsequently, dosing conditions, such as humidity, temperature and occlusion, also have their impact on the actual input (rate) of drug through human skin. Finally, all bits of information are combined to form a reasonably faithful picture of percutaneous absorption.

The effect of aging on percutaneous absorption in man

Despite much research into the mechanisms of cutaneous aging and the identification of significant age-associated biological and biophysical changes within the skin, the question "How does aging affect percutaneous absorption (PA) in vivo?" remains unanswered. We have made in vivo measurements of PA in young (18-40 years) and old (greater than 65 years) subjects. Standard radiotracer methodology was employed and PA was quantified from the urinary excretion profiles of 14C radiolabel (corrected for incomplete renal elimination). Testosterone (TST), estradiol (EST), hydrocortisone (HC), benzoic acid (BA), acetylsalicylic acid (ASA), and caffeine (CAFF) have been studied. Permeation of HC, BA, ASA, and CAFF was significantly (p less than 0.01, 0.01, 0.01, and 0.05, respectively) lower in aged subjects, whereas the absorption of TST and EST was similar in the two groups. Thus it appears that aging can affect PA in vivo and that relatively hydrophilic compounds are particularly sensitive. The diminished surface lipid content of "old" skin implies a diminished dissolution medium for compounds administered topically. It is reasonable to speculate that this physiologic change will impact most severely upon those permeants whose lipid solubility is lowest (that is, HC, BA, ASA, CAFF). Furthermore, the typically reduced hydration of aged stratum corneum will compound this effect for these chemicals. Conversely, highly lipid-soluble chemicals (TST and EST) may still be able to dissolve readily into the stratum corneum even when the available lipid medium is reduced.

Evaluation of the rat tail model for estimating dermal absorption of lindane

Dermal absorption of the insecticide lindane was determined following topical application of ring 14C-labeled lindane to the tail of Sprague-Dawley rats. The tail was tested as a practical alternative to the rat mid-dorsal (back) region, and the data obtained were compared to those with rat back and with those of rhesus monkeys in our previous reports. There was no significant difference between total percentage urinary 14C recovery for rats dosed on the tail with occlusive tail covers (52 +/- 6.2%; t1/2 = 2.7 d) compared to those with nonocclusive covers (55 +/- 4.4%; t1/2 = 2.9 d). Neither the total percentage urinary recovery nor the t1/2 values obtained for the rat tail and rat back models differed significantly. Carbon-14 activity was still detectable in urine samples taken after 72 d post-treatment. However, an extensive tissue analysis failed to demonstrate 14C activity persisting at 72 d, with the exception of trace levels detected in blood serum and tail tissue. Advantages of the rat tail model are highlighted.