Skin pharmacokinetics.
Explore the source record for details and available documents.
Administration, Cutaneous↗
Biomedical subjects
H Schaefer
Publications and source records attributed to H Schaefer.
Synergy effects between organic and inorganic UV filters in sunscreens.
The influence of the synergy effects between organic and inorganic UV filter substances on the sun protection factor (SPF) of topically applied sunscreen formulations is investigated. The medium is considered to have reflection, absorption, and scattering properties. The distribution of photons in this medium is investigated by Monte Carlo calculation. Typical optical parameters of the skin and substances are used to characterize the synergy effect. The results of the model calculation are checked by in vitro and in vivo measurements investigating the influence of different types of scattering microparticles on the absorption efficacy of topically applied formulations. It is found that the inorganic filter substances act as scattering microparticles in the upper skin layers. They increase the optical pathway of the photons in the topically applied absorbing formulation also localized there. In this way, more photons are absorbed, increasing the SPF. The results obtained are important for the optimization of the SPF of sunscreen formulation containing organic and inorganic UV-filter components.
Administration, Cutaneous↗
Bioequivalence of topical dermatological dosage forms--methods of evaluation of bioequivalence. AAPS/FDA Workshop on 'Bioequivalence of Topical Dermatological Dosage Forms-- Methods of Evaluating Bioequivalence', September 4-6, 1996, Bethesda, Md.
Explore the source record for details and available documents.
Administration, Cutaneous↗
Determination of the horny layer profile by tape stripping in combination with optical spectroscopy in the visible range as a prerequisite to quantify percutaneous absorption.
A new method was developed to determine the horny layer profile of volunteers using tape stripping in combination with UV/visible spectroscopy. The optical absorbance and the weight of corneocyte aggregates were compared as parameters for the determination of the mass of the horny layer particles fixed to the individual tapes. It was shown that the potential disturbances influencing both parameters must be considered critically before calculating the correlation factor, found as R2mean = 0.93 +/- 0.05. It was proven that the absorbance in the visible range is better suited than the weight to quantify the amount of corneocyte aggregates removed by a single strip. The new method allows an exact anatomical localization of the individual tapes and all data obtained within the depth profile of the stratum corneum. This was exemplified by the determination of the penetration of chemical and physical UV filters into the horny layer.
Adult↗
Bioavailability of clobetasol propionate-quantification of drug concentrations in the stratum corneum by dermatopharmacokinetics using tape stripping.
The concentration of clobetasol propionate in the stratum corneum after application of three different formulations was determined, quantifying the influence of the formulations on the bioavailability of the drug. The stratum corneum was sampled by tape stripping. The concentrations of clobetasol propionate were determined quantitatively by HPLC. After application of Clobetasol Propionate Cream USP, 0.05%, and Temovate Cream, 0.05%, identical amounts of the drug were found in the stratum corneum, whereas after application of Temovate epsilon Emollient, 0.05%, the quantity was clearly decreased. From results obtained measuring the drug concentration in the adjacent sites of the skin where the creams had not been applied, it became clear that clobetasol propionate in Temovate epsilon Emollient, migrated to a large extent in the lateral direction. This explains the lower concentration measured for this formulation in the skin areas where the cream had been applied. In general, a lateral distribution of the applied drug must be taken into account when positioning the application areas on the forearm.
Administration, Cutaneous↗
Percutaneous absorption of sunscreens in vitro: interspecies comparison, skin models and reproducibility aspects.
Appropriate evaluation of sunscreens is required to provide better knowledge of their safety and efficacy. One of the most important elements of this evaluation is the assessment of percutaneous absorption. In vitro methods are largely used for such assessments, and the accuracy of the measurements generated with these methods depends on the use of a proper methodology. This study was designed to evaluate an in vitro protocol for investigating the percutaneous absorption of two sunscreens under standardized experimental conditions. Octyl methoxycinnamate and benzophenone 4 were each incorporated in a typical oil-in-water emulsion and tested separately. Salicylic acid was tested as a reference compound. In vitro percutaneous absorption was evaluated using two species, the pig and human, and two models, full-thickness and split-thickness skin. The reproducibility of study results was evaluated by comparing the data generated by two industrial laboratories, L'Oréal and Hoffmann-La Roche. The correlation of quantitative data between pig skin and human skin was very good, and the split-thickness skin model seemed to be more appropriate for measuring the absorption of sunscreens. Results obtained for salicylic acid demonstrated the relevance of the protocol in terms of prediction of in vivo percutaneous absorption. Finally, the comparison of pig skin data between the two laboratories demonstrated a good correlation and underlined the need for a standardized in vitro procedure.
Animals↗
The stripping technique: in vitro absorption and penetration of five UV filters on excised fresh human skin.
This article gives the results of a study whose aim was to compare the compartmental distribution and absorption of 5 UV filters, in vitro, by fresh human skin, after exposure times of 30 min and 16 h. These UV filters from BASF (octyl methoxycinnamate, benzophenone 4, benzophenone 3, octyl triazone and octocrylene) were incorporated separately in a simple oil-in-water emulsion. The composition of the emulsions was designed in order to obtain a sun protection factor of 5. Therefore the UV filters were introduced into the emulsions at different concentrations. We show that the affinity for each skin level [stratum corneum (SC), viable epidermis, dermis and receptor fluid] is different according to the test substance used. Some substances accumulated in the SC, whereas others passed through the skin very quickly and were quantified in the receptor fluid. The stripping technique allowed us to see that more than 94% of the chemical compound in the SC was in the first eight tapes. The problem of individual values below the limit of detection was raised, a correlation between the two exposure times was found (y = 1.702x - 0.105; R = 0.94) and a classification of products according to their affinity for the SC was determined.
Adult↗
Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice.
Coated titanium dioxide (TiO2) microparticles are commonly used as UV filter substances in commercial sunscreen products. The penetration of these microparticles into the horny layer and the orifice of the hair follicle was investigated. The distribution of the microparticles in the horny layer was analyzed using the method of tape stripping in combination with spectroscopic measurements. Deeper layers of the stratum corneum were devoid of TiO(2) even after repetitive application of sunscreen preparation when analyzing interfollicular areas. Only in the areas of the pilosebaceous orifices could microparticles be identified. The penetration of TiO(2) was investigated in histological skin sections. A biopsy was taken from a skin area from which the horny layer had been removed by tape stripping. In isolated areas, a penetration of coated TiO2 into the open part of the follicle was observed. The amount of TiO2 found in a given follicle was less than 1% of the applied total amount of sunscreens. A penetration of microparticles into viable skin tissue could not be detected.
Adult↗
Evaluation of the pseudo-absorption method to quantify human stratum corneum removed by tape stripping using protein absorption.
Tape stripping is a well-known method to study the barrier function of the stratum corneum (SC) and penetration processes of topically applied substances into the horny layer. The quantification of the removed corneocytes for each tape strip is the prerequisite for these studies. The pseudo-absorption of the corneocytes was proposed as a measure for the quantification of the removed corneocyte aggregates. In this study, the pseudo-absorption of the corneocytes in the visible range (430 nm) is compared with the protein absorption in the UV range (278 nm) and an absorption at 652 nm obtained after staining of the SC proteins with Trypan blue. Both the protein absorption and the absorption measured after staining correlate well with the pseudo-absorption measured at 430 nm (R(2) = 0.92 +/- 0.04 and R(2) = 0.95 +/- 0.04, respectively).
Adult↗
Penetration of vitamin A acid into human skin.
Explore the source record for details and available documents.
1-Propanol↗
[Theory of methods to compare lead fields in electrocardiography (author's transl)].
A method is theoretically described to test the accuracy of various lead system of the ecg. The priniciple of this method consists in the following procedure. The heart position is changed maximally in a proband by varying the position of the body and by deep inspiration and exspiration. If the lead field is parallel, the recorded vector loops should by conventible into each other by merely rotating them electronically, because the cardiac determinants of the veg will scarcely be changed by a change in heart position. The deformations of the veg in the edgeside and broadside view are an appropriate measure of the inhomogenities (the "accuracy") of the lead field, mostly caused by the configuration of the chest and the inhomogeneous conductivity of the tissues and the resulting lack of parallelity in the lead lines of the field. Criteria to test the form of the vector loop are developed, measuring quantitatively the similarly of the loops recorded in different heart positions. The "best" lead is regarded to be that with greatest similarity of the loops in extreme dislocations of the heart.
Electrocardiography↗
[Clinical trials in dermatology. The phase I trials].
Application of the new topical product on the diseased skin should be preceded by its safety evaluation on the healthy skin in human volunteers. We propose here guidelines for the evaluation of the irritation, sensitization, phototoxicity and photoallergy potentials for topical products. The methods for evaluation of percutaneous absorption are also discussed. The studies presented here are not the object of any regulations. Therefore, we propose here an approach for the safety evaluation of topical products in human volunteers.
Administration, Topical↗
[Clinical trials in dermatology. Evaluation of the tolerability and efficacy of a topical anti-inflammatory treatment in atopic dermatitis].
Study designs for assessment of topical anti-inflammatory drugs in atopic dermatitis are discussed. Atopic dermatitis is a chronic disease with symmetrically distributed lesions. In order to avoid individual and spontaneous variation and to obtain an early impression of the efficacy of a new topical drug, bilaterally paired lesions can be used. Further drug development requires controlled double-blind parallel group design. General recommendations regarding inclusion criteria, and the measurement of efficacy and safety parameters are presented. Methods available for data evaluation and the particularities of different clinical designs are discussed.
Administration, Topical↗
[Clinical trials in dermatology. Evaluation of the tolerability and efficacy of a topical antipsoriatic treatment].
There has been considerable variations between different authors in the evaluation of antipsoriatic therapies. Improvement homogeneity must be achieved in this field. The main specific methods have been investigated: inclusion criteria, assessment of disease progress and safety parameters in phase II and III clinical trials, evaluating antipsoriatic treatment.
Administration, Topical↗
[Clinical trials in dermatology. Evaluation of the tolerability and efficacy of a topical antifungal agent in the treatment of superficial mycoses].
There is no single method for evaluating topical antifungal drugs. The localisation and the type of fungal, determine the treatment duration (from few days to several months). The main methodological characteristics of clinical trials in tinea pedis treatment (athlete's foot type) are reported. Aspects related to other clinical forms such as tinea versicolor and onychomycosis are also described. In any case, the main criteria of activity remains the mycological examination based on KOH microbiology and culture performed at the end of the treatment and again afterwards.
Administration, Topical↗
[Clinical trials in dermatology. Statistical support].
To determine the efficacy or safety of new topical treatments, more or less standardized studies must be performed. This article presents several examples of statistical analyses of the data currently seen in the dermatology area, and some guidelines for study sample size determination. More importantly, it indicates, for as soon as phase I studies, the need for preliminary informations such as development strategy, historical data, literature references or pilot studies, to determine or adapt appropriate designs and sample sizes. This need can be filled by close collaboration among clinicians, statisticians and sponsor.
Clinical Trials as Topic↗
[Clinical trials in dermatology. Evaluation of the tolerability and efficacy of a topical anti-acne].
Acne is a frequent dermatologic disease of the teenagers. Methodology of antiacne preparations clinical trials has evolved recently, leading to better comprehension of acne treatment on acne lesions. The main rules for good clinical evaluation of acne treatments are: an objective counting of each individual lesions on a defined area (face, back), a global acne assessment, a therapy duration from 1 to 3 months or more, a skin safety evaluation for erythema, desquamation, dryness, itching, burning and oiliness with a 0 to 3 scoring system.
Acne Vulgaris↗
[Effect of right cervical sympathectomy on the uptake of iodine 131 by the thyroids of adrenalectomized female rats].
Explore the source record for details and available documents.
Adrenal Glands↗