Gain or loss? Sunscreen efficiency after cosmetic pretreatment of the skin.

Sunscreens are a key pillar of the multimodal protection strategy against short- and long-term impacts of intermittent and continuous UV exposure. Hitherto, an unanswered part of current scientific discourse is the question whether a cosmetic pretreatment has an impact on distribution and adhesiveness of sunscreens on the skin and therefore affects UV protection. In order to evaluate the homogeneity of sunscreen filter distribution, water resistance as a parameter of adhesiveness and effective UV protection of sunscreens after a pretreatment with cream or lotion was investigated in 18 volunteers who were examined before and after swimming, using the established combination of the tape stripping procedure and UV/VIS spectroscopy. It was shown that a cosmetic skin pretreatment affects neither filter homogeneity nor effective UV protection prior to water contact. However, compared to nonpretreated skin, a considerable loss of water resistance is caused. Therefore, using a cream or lotion before application of sunscreens is not to be recommended.

Methods for the evaluation of the protective efficacy of sunscreen products.

The objective of the present investigation was to examine the utilization of optical and spectroscopic methods for the noninvasive characterization of Anthelios XL Fluide Extreme (SPF 50+), an exemplary sunscreen, concerning its homogeneity of distribution on the skin, its spectroscopic properties and its overall protective efficacy. The homogeneity of the distribution of the sunscreen on the skin was investigated with a multiphoton tomography microscope. Additionally, the sum transmission spectrum was determined using tape stripping and spectroscopic measurements. The results revealed a very homogeneous distribution of the sunscreen on the skin surface and also in the deep furrows. The sum transmission spectrum reflects a high protective efficacy of the sunscreen in both the UVA and UVB ranges. The sunscreen Anthelios XL Fluide Extreme (SPF 50+) generates a comfortable feeling on the skin and can be easily distributed. The presented optical methods have been shown to be suitable to investigate the overall protective efficacy of sunscreen products objectively, noninvasively and quickly.

Quantification of the inhomogeneous distribution of topically applied substances by optical spectroscopy: definition of a factor of inhomogeneity.

The inhomogeneous distribution of topically applied substances due to decisive differences in the skin structure (furrows and wrinkles) affects the efficacy of cosmetic products, in particular sunscreens. The combination of tape stripping and optical spectroscopy results in absorption data, which reflect ex vivo the inhomogeneity of the in vivo distribution of topically applied substances. Based on these data, a factor of inhomogeneity is defined describing the individual distribution of formulations on the skin surface of volunteers. Thus, the influence of different skin surface structures and the influence of different formulations on the distribution of the topically applied substances can be determined. Analyzing the inhomogeneity data on 6 volunteers (5 sunscreens per volunteer), it was found that the influence on the distribution of sunscreens caused by the formulation was higher than the inhomogeneity originating from the differences in the skin surface structure of the volunteers. The method is well suited to characterize, for example, sunscreens and antiaging creams in the process of development, as well as for the evaluation of the final products.

In vivo methods for the analysis of the penetration of topically applied substances in and through the skin barrier.

The efficacy of a drug is characterized by its action mechanism and its ability to pass the skin barrier. In this article, different methods are discussed, which permit this penetration process to be analysed non-invasively. Providing qualitative and quantitative information, tape stripping is one of the oldest procedures for penetration studies. Although single cell layers of corneocytes are removed from the skin surface, this procedure is considered as non-invasive and is applicable exclusively to the stratum corneum. Recently, optical and spectroscopic methods have been used to investigate the penetration process. Fluorescence-labelled drugs can be easily detected in the skin by laser scanning microscopy. This method has the disadvantage that the dye labelling changes the molecular structures of the drug and consequently might influence the penetration properties. The penetration process of non-fluorescent substances can be analysed by Raman spectroscopy, electron paramagnetic resonance, CARS and multiphoton microscopic measurements. Using these methods, the concentration of the topically applied formulations in different depths of the stratum corneum can be detected by moving the laser focus from the skin surface deeper into the stratum corneum. The advantages and disadvantages of these methods will be discussed in this article.

Pathways of lateral spreading.

In the case of topically applied substances, usually both lateral spreading and competitive penetration into the skin occur in parallel. In the present study, the pathways of lateral spreading were studied quantitatively and visually. The local distribution and lateral spreading of the UV filter substance butyl methoxydibenzoylmethane applied in an o/w emulsion was studied on the forearm and the back. The tape stripping procedure was used to determine the recovery rates inside and outside the area of application. The skin characteristics of transepidermal water loss, pH value, hydration of the stratum corneum and sebum rate were determined at both anatomic sites. Photography and laser scanning microscopy were used to visually investigate the lateral spreading of topically applied dyes. On the back, a preferred direction of lateral spreading parallel to the body axis was observed. This result was caused by differences in the network of furrows. The furrows functioned as a pathway for lateral spreading, whereas the follicles formed a reservoir for the topically applied substance.

Penetration studies of topically applied substances: Optical determination of the amount of stratum corneum removed by tape stripping.

Tape stripping is a standard measuring method for the investigation of the dermatopharmacokinetics of topically applied substances using adhesive films. These tape strips are successively applied and removed from the skin after application and penetration of topically applied substances. Thus, layers of corneocytes and some amount of topical applied substances are removed. The amount of substances and the amount of stratum corneum removed with a single tape strip has to be determined for the calculation of the penetration profile. The topically applied substances removed from the skin can be determined by classical analytical methods like high-pressure liquid chromatography, mass spectroscopy, and spectroscopic measurements. The amount of corneocytes on the tape strips can be easily detected by their pseudoabsorption. In the present paper, an easy and cheap corneocyte density analyzer is presented that is based on a slide projector. Comparing the results of the measurements obtained by the corneocyte density analyzer and by uv-visible spectrometry, identical results were obtained.

Increased bioavailability of oral melatonin after fluvoxamine coadministration.

BACKGROUND: Fluvoxamine, a selective serotonin reuptake inhibitor, is known to elevate melatonin serum concentrations. It has not been clear whether these effects might be attributed to an increased melatonin production or to an decreased elimination of melatonin. The latter hypothesis was tested by this study. METHODS: Five healthy male volunteers (one CYP2D6 poor metabolizer) received 5 mg melatonin either with or without coadministration of 50 mg fluvoxamine. Serum concentrations of melatonin and fluvoxamine were assessed from 0 to 28 hours after melatonin intake. RESULTS: Coadministration of fluvoxamine, on average, led to an 17-fold higher (P < .05) area under concentration-time curve (AUC) and a 12-fold higher (P < .01) serum peak concentration (Cmax) of melatonin. The terminal elimination half-life was not significantly affected. The AUC and Cmax of fluvoxamine were about three times higher and the half-life was about two times higher in the poor metabolizer. There was a correlation (r = 0.63; P < .01) between the melatonin and fluvoxamine serum concentrations. The poor metabolizer was found to have a more pronounced and longer-lasting effect of fluvoxamine on the pharmacokinetics of melatonin. CONCLUSION: This study showed an increase in the bioavailability of oral melatonin by coadministration of fluvoxamine. The effects of fluvoxamine on the melatonin serum concentrations in patients with depression might therefore be caused by inhibition of the elimination of melatonin and not attributable to an increased production of melatonin.

Chronical haloperidol and clozapine treatment in rats: differential RNA display analysis, behavioral studies and serum level determination.

1. Adult, female rats were treated orally for 23 days with 1.6 mg/kg haloperidol or 36 mg/kg clozapine per day, to study chronic effects of the two neuroleptics. 2. At five time points during the neuroleptic treatment, animal behavior was recorded in an open field and locomotive activity was analysed. At the end of the experiment, rats were decapitated, blood samples were collected and serum concentrations of haloperidol and clozapine were determined by a radioreceptor or HPLC assay, respectively. RNA was isolated from each brain, without cerebellum, and subjected to differential RNA display. 3. Mean serum concentrations were 8 ng/ml for haloperidol and 21 ng/ml for clozapine. Analysis of open field behavior showed that haloperidol and clozapine decreased the total distance moved and the velocity as measures of the overall activity, whereas the number of rearings and the number of entries into the center, reflecting risk assessment behavior, were differentially affected. Three neuroleptic-regulated gene fragment bands were identified in differential RNA display experiments. Two gene fragments of 281 bp and 266 bp were sequenced. 4. We conclude that our study design that used behavioral, pharmacokinetic and molecular analysis increase the likelihood of finding relevant molecular events underlying the pharmacotherapeutic effects of neuroleptics in animal models.

Steady state concentrations of clomipramine and its major metabolite desmethylclomipramine in rat brain and serum after oral administration of clomipramine.

Twenty male Sprague-Dawley rats received five oral doses of clomipramine 20 mg/kg at 4-h intervals. The animals were decapitated 1, 2, 3, 5 and 12 h after the last dose for determination of clomipramine and desmethylclomipramine in serum and frontal cerebral cortex. Time dependent concentrations of clomipramine and desmethylclomipramine paralleled in serum and brain. Half-lives were similar in serum and brain with 7.8 versus 6.2 h and 5.5 versus 5.0 h for clomipramine and desmethylclomipramine, respectively. Absolute concentrations, however, were markedly higher in brain than in serum - 12.5 fold for clomipramine and 7.4 fold for desmethylclomipramine. The data indicate that serum and brain concentrations of clomipramine and its demethylated metabolite are rapidly exchanged between blood and brain. Assuming that blood and brain kinetics in man and rat are comparable, it is concluded that monitoring blood concentrations of clomipramine and desmethylclomipramine is a useful way to evaluate brain concentrations.

Distribution of clozapine and desmethylclozapine between blood and brain in rats.

Desmethylclozapine is the major metabolite of clozapine in serum. Although the metabolite is pharmacologically active in vitro, the occurrence of desmethylclozapine in brain under steady-state conditions and its role for clinical actions of clozapine are unclear. In this study 20 male Sprague-Dawley rats received five oral doses of clozapine 20 mg/kg at 1.5-h intervals. At 0.5, 1, 2 and 5 h after the last administration, at a time four animals were killed for analysis of clozapine and desmethylclozapine concentrations in serum and brain. The treatment yielded steady-state serum concentrations of clozapine that are considered as therapeutically effective in man. Desmethylclozapine concentrations exceeded those of clozapine at 2-5 h after drug application. In brain, drug concentrations were 15.8-fold higher for clozapine than in serum, but only 2.7-fold higher for desmethylclozapine. The brain clozapine concentrations exceeded those of desmethylclozapine by about 3 times. These data indicate that desmethylclozapine is unlikely to play a role for CNS-mediated effects.

Combination treatment with clozapine and paroxetine in schizophrenia: safety and tolerability data from a prospective open clinical trial.

Clozapine is a drug with many side effects, some of them with potentially hazardous outcome (e.g. seizures, agranulocytosis), if not carefully monitored. It has been shown that the metabolism of clozapine may be affected by concomitant treatment with selective serotonin reuptake inhibitors (SSRIs), while there have been reports of improved efficacy on negative symptomatology of clozapine in combination with SSRIs. Therefore, this prospective open clinical trial was performed to investigate the safety and tolerability of the coadministration of clozapine and paroxetine under control of serum concentrations of clozapine and its metabolites and the effect of this combination treatment on psychopathological outcome was evaluated. A total of 14 patients suffering from schizophrenia or schizodepressive disorder with predominant negative symptomatology were included. The duration of the study was at least 6 weeks for each patient. Initial treatment was a monotherapy with clozapine at a daily dose of 2.5 mg/kg weight. After two measurements of serum concentrations of clozapine and metabolites during steady state conditions, an add-on therapy with 20 mg paroxetine was initiated. No concomitant medication was allowed. The main finding of our prospective study was that addition of paroxetine to a monotherapy with clozapine was a well tolerated medication that did not give rise to new clinically relevant side effects. After addition of paroxetine the serum concentrations of clozapine and its major metabolites remained virtually constant. The results of the psychopathological measurements indicated a further clinical improvement, although the small open study could not test for efficacy.

Influence of aromatic hydrocarbons on the metabolism of dichloromethane to carbon monoxide in rats.

The influence of prior or simultaneous oral administration of benzene, toluene, o-, m-, or p-xylene on the carboxyhemoglobin (COHb) level after a single dose of dichloromethane (DCM) was investigated in male rats. Six hours after administration of DCM, 6.2 mmol/kg, the mean maximum COHb level was 9.3 +/- 1.9%. This level was significantly enhanced by prior administration of benzene (16.9 mmol/kg) at 12-24 h, of toluene (18.8 mmol/kg) at 20-28 h, of o- (16.6 mmol/kg) and m-xylene (16.3 mmol/kg) at 20-32 h, and of p-xylene (16.2 mmol/kg) at 24-32 h. The corresponding maximum COHb levels were 20.7 +/- 1.3, 18.6 +/- 1.1, 18.9 +/- 1.1, 22.7 +/- 1.2, and 13.2 +/- 1.0%, respectively. After simultaneous administration of both DCM and the aromatic solvent, the COHb formation was inhibited: values of 1.3 +/- 0.3, 1.7 +/- 0.4, 3.6 +/- 0.2, 1.9 +/- 0.2, and 2.0 +/- 0.2% COHb, respectively, were found. The inhibition was also evident when DCM was administered 12 h after toluene or m-xylene and 12, 16 or 20 h after p-xylene. The inhibition was dose-related as seen after combined gavage of o-, m-, or p-xylene and DCM. The o- and m-, but not the p-methylhippuric acid (MHA) excretion in the urine was significantly reduced after simultaneous administration of equimolar doses of DCM and the corresponding xylenes. In conclusion, it seems that the stimulation or inhibition of the COHb formation after DCM caused by pretreatment with or by simultaneous administration of the aromatic solvents is due to the induction of cytochrome P-450 IIE1 or to competition between DCM and the aromatic solvent on this isozyme of cytochrome P-450.

The tape stripping procedure--evaluation of some critical parameters.

Tape stripping is a simple and efficient method for the assessment of quality and efficacy of cosmetical and dermatological formulations. After topical application and penetration of formulations, the cell layers of the stratum corneum are successively removed from the same skin area using adhesive films. The tape strips contain the amount of corneocytes and the corresponding amount of the penetrated formulation, which can be determined by classical analytical chemical methods. Different formulations can strongly influence the amount of stratum corneum removed with every tape strip. Therefore, it is essential for the comparison of the penetration of different formulations that the amount of formulation detected on the single tape strip is not related to the tape strip number as a relative measure of the penetration depths, but to their standardized real position in the stratum corneum. Therefore, different methods are reported for the determination of the amount of stratum corneum removed with every tape strip. The tape stripping method in its standardized form is well-suited to determine the dermatopharmacokinetics of topically applied substances. Additionally, the method can be used to obtain information about the homogeneity and the distribution of formulations on the skin and in the stratum corneum. This is used, e.g., for the determination of the homogeneity of the distribution and the ex vivo determination of a universal sun protection factor (USPF) characterizing the efficacy of sunscreens.

Region specific distribution of levomepromazine in the human brain.

OBJECTIVE: The aim of this study was to examine concentrations of levomepromazine and its metabolite desmethyl-levomepromazine in different regions of human brain and in relationship to drug-free time. METHODS: Drug concentrations were measured in up to 43 regions of 5 postmortem human brains of patients previously treated with levomepromazine. To enable statistical comparison across brain regions several smaller brain areas were put together to form larger brain areas (cortex cerebri, limbic system, cerebellum, basal ganglia, thalamus). Mean values of drug concentrations in these larger brain areas were used in a repeated measurement ANOVA to analyze for region specific distribution. The elimination half-life in brain tissue was estimated with a NONMEM population kinetic analysis using the mean value of all brain regions of an individual case. RESULTS: Levomepromazine and desmethyl-levomepromazine appear to accumulate in human brain tissue relative to blood. Mean concentrations differed largely between individual brains, in part due to differences in dose of drug, duration of treatment and drug-free time before death. There was an apparent region-specific difference in levomepromazine concentrations with highest values in the basal ganglia (mean 316 ng/g) and lowest values in the cortex cerebri (mean 209 ng/g). The elimination half-life from brain tissue is longer than from blood and was calculated to be about one week. Similar results were obtained with desmethyl-levomepromazine. CONCLUSIONS: Levomepromazine shows a region-specific distribution in the human brain with highest values in the basal ganglia. This might be the consequence of low expression of the metabolic enzyme Cyp2D6 in the basal ganglia. If this finding is true also for other neuroleptic drugs it might increase our understanding of preferential toxicity of neuroleptic drugs against basal ganglia structures and higher volumes of basal ganglia of neuroleptic-treated patients. Furthermore, patients exposed to levomepromazine cannot be considered to be free of residual effects of the drug for a number of weeks after withdrawal.

Comparison of transepidermal water loss and spectroscopic absorbance to quantify changes of the stratum corneum after tape stripping.

The objective and quantitative application of tape stripping in pharmaceutics and dermatopharmacokinetics requires the determination of the exact position of each removed tape strip inside the stratum corneum (SC) and/or the determination of the relative SC thickness. In this study, transepidermal water loss (TEWL) and the optical spectroscopic data of the corneocytes were measured simultaneously during the complete removal of the SC by tape stripping. The spectroscopic data quantitatively reflect the amount of corneocytes removed by the individual tape strips, whereas TEWL and 1/TEWL are not sensitive enough to measure the relatively small changes in the SC thickness realized by the removal of the individual strips. The relative SC thickness can be determined directly by the spectroscopic data, while the 1/TEWL values require a second independent method. The results demonstrate the importance of tape stripping characterizing the behaviour of topically applied substances.

Reservoir function of the stratum corneum: development of an in vivo method to quantitatively determine the stratum corneum reservoir for topically applied substances.

Investigations on the stratum corneum (SC) reservoir for topically applied substances are of importance in dermatologic science in order to assess the pharmacokinetics of these substances. In the present study, an in vivo method was developed to determine the SC reservoir quantitatively and to investigate the temporal behavior of this reservoir. Therefore, increasing amounts of an oil-in-water emulsion (o/w emulsion) containing 4% of a chemical UV filter were topically applied onto the flexor forearms of 5 healthy volunteers. The saturation of the SC reservoir was determined utilizing the tape stripping technique 1 and 6 h after application. The capacity of the SC reservoir for the o/w emulsion was found to be approximately 2.7 mg/cm(2). Furthermore, a correlation of the capacity of the SC with transepidermal water loss was observed. Extending the time between the topical application and SC removal did not affect the distribution or the recovery rate of the UV filter in the SC. The results indicate that the reservoir of the SC is limited. This is reflected by the saturation level, which depends on the individual volunteer and, presumably, the topically applied substances and formulations used. The results show that the method developed is suited to quantitatively determine in vivo the SC reservoir for topically applied substances.

Estimation of the relative stratum corneum amount removed by tape stripping.

BACKGROUND/PURPOSE: The tape stripping procedure is a suitable minimal invasive tool to study, e.g. the penetration and dermatopharmacokinetics of topically applied substances. In the present study, this procedure was used to remove the stratum corneum (SC) completely and to study the penetration of the UVA filter substance butyl methoxydibenzoylmethane after application in two different vehicles. METHODS: The amount of corneocytes removed by each tape strip from the flexor forearm of human volunteers was determined via their pseudo-absorption. In a second part, the penetration profiles of a UVA filter substance applied in two different vehicles were determined following the developed standard protocol using the tape stripping procedure in combination with UV/VIS spectroscopy. RESULTS: The amount of corneocytes removed by each tape strip was related to the number of tape strips used for removal. Mean values with a deviation of less than 20% concerning the relative amount of SC removed by a constant number of tape strips were obtained. For instance, a relative amount of 66 +/- 12% was removed with the first 20 tape strips, while nearly the complete SC (95 +/- 3%) was removed using 50 tape strips. In addition, these results were used to estimate the relative SC amounts removed, studying the penetration of the UVA filter substance after application in two different vehicles. No significant differences between the distributions of the UV filter substance applied in both emulsions were obtained (P > 0.05). CONCLUSIONS: The reported procedure for the estimation of the removed SC amount provides the possibility to avoid the complete removal of the SC and to compare the penetration characteristics obtained for different volunteers and different products in relation to the relative horny layer profile.