Pharmacokinetics of Transdermal Etofenamate and Diclofenac in Healthy Volunteers.

Little is known about the course of the plasma concentration and the bioavailability of non-steroidal anti-inflammatory drugs (NSAIDs) contained in dermal patches. We compared an etofenamate prototype patch (patent EP 1833471) and a commercially available diclofenac epolamine patch regarding the bioavailability of the active ingredients relative to respective i.m. applications and regarding their plasma concentration-time course. Twenty-four healthy human volunteers were treated using a parallel group design (n = 12 per group) with a single dermal patch (removed after 12 hr) followed (after a latency of 48 hr) by eight consecutive dermal patches every 12 hr to reach steady-state conditions. The patches were generally well tolerated, but one volunteer treated with etofenamate developed an allergic contact dermatitis. After the first patch, Cmax was 0.81 ± 0.11 (mean ± S.E.M.) ng/mL (reached 12 hr after patch removal) for diclofenac and 31.3 ± 3.8 ng/mL for flufenamic acid (reached at patch removal), the main metabolite of etofenamate. Etofenamate was not detectable. After repetitive dosing, trough plasma concentrations after the eighth dose were 1.72 ± 0.32 ng/mL for diclofenac and 48.7 ± 6.6 ng/mL for flufenamic acid. Bioavailabilities (single dose) relative to i.m. applications were 0.22 ± 0.04% for diclofenac and 1.15 ± 0.06% for flufenamic acid. In conclusion, the relative bioavailability (compared to the respective i.m. application) of both drugs is low. The maximal plasma concentrations after topical administration of these drugs are well below the IC50 values for COX-1 and COX-2, explaining the absence of dose-dependent toxicities.

Novel Drug Delivery System for Dermal Uptake of Etofenamate: Semisolid SLN Dispersion.

BACKGROUND: Semisolid SLNs are novel strategy for dermal drug administration instead of incorporating the SLN dispersions into conventional semisolids. Etofenamate loaded semisolid SLNs were successfully prepared and in vitro characterization of formulations were performed in our previous study. The present study is an attempt to evaluate the dermal behavior of the semisolid SLNs selected on the basis of previous research and investigate the properties in terms of the convenience for topical applications. OBJECTIVE: The objective of this study is to evaluate the skin penetration characteristics of semisolid SLN formulations. The occlusive and mechanical properties of semisolid SLNs were also evaluated because of their impression on the dermal behavior of the formulations. METHOD: The occlusive properties were investigated by in vitro occlusion test. Texture analysis was performed to define the hardness, compressibility, adhesiveness, cohesiveness and elasticity of the formulations. Rat skin was chosen to evaluate the ex vivo penetration of etofenamate loaded semisolid SLNs and commercial gel product. Coumarin-6 was used to visualize the dermal distribution of the semisolid SLN formulations. For monitorizing the penetration of coumarin-6 into the skin samples Confocal Laser Scanning Microscopy was employed. RESULTS: The occlusive and mechanical properties of C1 coded semisolid SLN formulation were found more favorable in comparison with P1. The cumulative etofenamate amount in skin samples was found to be 39.88 ± 1.50 µg/cm2 for C1 and 30.56 ± 2.10 µg/cm2 for P1 coded formulations. According to CLSM images, greater fluorescence intensities and deeper skin penetrations were obtained with both of the semisolid SLNs in comparison to plain Carbopol gel. CONCLUSION: It can be concluded that the semisolid SLNs are promising alternative dermal drug delivery systems to the conventional dosage forms.

Effects of permeation enhancers on flufenamic acid delivery in Ex vivo human skin by confocal Raman microscopy.

For effective topical delivery, a drug must cross the stratum corneum (SC) barrier into viable tissue. The use of permeation enhancers is a widespread approach for barrier modification. In the current study, flufenamic acid (FluA), a non-steroidal anti-inflammatory drug, is a model agent for investigating the influence of hydrophobic versus hydrophilic enhancers. In separate experiments, FluA in octanol or propylene glycol/ethanol (75/25) is applied to the SC for varying times followed by confocal Raman microscopic mapping of drug and enhancer penetration and spatial distribution. Deuterated versions of the enhancers permit us to spectroscopically distinguish the exogenous chemicals from the endogenous SC lipids without affecting penetration parameters. The FluA pathway is tracked by the CC stretching mode at ∼1618cm(-1). Discrete, small inclusions of both enhancers are observed throughout the SC. High concentrations of FluA are co-localized with octanol domains which appear to provide a pathway to the viable epidermis for the drug. In contrast, FluA concentrates in the upper SC when using the hydrophilic agent and endogenous lipids appear unperturbed in regions outside the enhancer pockets. The ability to examine perturbations to endogenous ultrastructure and molecular structure in skin while tracking penetration pathways provides insight into delivery mechanisms.

Diphenylalanine peptide nanotubes self-assembled on functionalized metal surfaces for potential application in drug-eluting stent.

This study focuses on the potential of diphenylalanine self-assembled peptide nanotubes (FF Nts) for delivery of flufenamic acid (FA) from metal implants. Self-assembly of FF Nts was studied in solution and on surfaces of glass, silicone and gold substrates. FA was loaded inside the shell of FF Nts and subsequently FF/FA Nts were attached to gold surfaces. The substrate were characterized by Field Emission Scanning Electron Microscopy (FESEM), fluorescence microscopy, confocal microscopy, and UV-vis spectroscopy. Release of FA from FF Nts were investigated by immersing coated metal substrates in phosphate-buffered saline for 12 days. Self-assembly of FF in water and solvent resulted in formation of nanotubes, which efficiently loaded 98% of FA with concentration of 20 µg/mL. FESEM images confirmed successful attachment of FF/FA Nts to functionalized gold substrates. In vitro release studies indicated using FF Nts has prolonged the release rate of FA for several days. Biocompatibility studied confirmed more than 50% of the cells were alive in concentration of 250-1000 µg/mL of FF Nts thus suggesting the potential of peptide based self-assemble nanostructures as an alternate system for polymer coating in drugs eluting stents. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2280-2290, 2016.

Eight-channel transceiver RF coil array tailored for ¹H/¹9F MR of the human knee and fluorinated drugs at 7.0 T.

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1)H/(19)F MR of the human knee at 7.0 T following application of (19)F-containing drugs. The (1)H/(19)F RF coil array includes a posterior module with two (1)H loop elements and two anterior modules, each consisting of one (1)H and two (19)F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19)F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) ­ a (19)F-containing non-steroidal anti-inflammatory drug ­ to determine T1 and T2 and to study the (19)F signal-to-dose relationship. The suitability of the proposed approach for (1)H/(19)F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. Q(L)/Q(U) was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1)H/(19)F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19)F-containing medicinal compounds in vivo.

Topical gels of etofenamate: in vitro and in vivo evaluation.

Non-steroid anti-inflammatory drugs (NSAIDs), such as etofenamate, are among the most prescribed drugs used for their analgesic, anti-rheumatic, antipyretic and anti-inflammatory properties. Topical formulations have the main advantage of targeted delivery. However, drugs must overcome the skin due to its role as a physical and chemical barrier against the penetration of chemicals and microorganisms. This barrier must be altered to allow the permeation of drugs at a suitable rate to the desired site of activity. Permeation modulators can intercalate the skin outer layers causing structure disruption, opening an energetically favourable route for the drug to diffuse through. The aim of this work was the development of hydroalcoholic gels containing 5.0% (w/w) of etofenamate for topical administration with anti-inflammatory activity and enhanced drug delivery. The physical and chemical characterization, in vitro release and permeation studies and in vivo anti-inflammatory activity were assessed. The gel with 30% ethanol showed in vivo anti-inflammatory activity with suitable physical chemical and microbiologic characteristics. In vitro release and permeation studies revealed that the different amounts of ethanol used influenced the release profiles of etofenamate. Moreover, it was demonstrated that this formulation is an adequate vehicle for the etofenamate skin permeation.

Application of quantitative (19) F nuclear magnetic resonance spectroscopy in tape-stripping experiments with natural microemulsions.

The skin penetration of flufenamic acid (Fluf) and fluconazole (Fluc) from innovative natural microemulsions was investigated in tape-stripping experiments on pig ears. The formulations were based on the eudermic surfactants lecithin, sucrose laurate, alkylpolyglycoside or a mixture thereof. The quantification of the penetrated drug amounts was executed by (19) F nuclear magnetic resonance (NMR) in comparison with high-performance liquid chromatography (HPLC). The data obtained by the (19) F NMR method were confirmed by additional quantitative studies using HPLC. An excellent linear correlation was found for Fluf as well as for Fluc between (19) F NMR and HPLC data. This work presents a strategy outlining the use of (19) F NMR to selectively monitor the skin penetration routes of fluorinated compounds. Fluc penetrated generally well into the stratum corneum with the significantly highest amounts from the sucrose laurate microemulsion on the tape strips 1-5. Similarly, the highest amounts of penetrated Fluf could be observed from the formulation based on sucrose laurate. In addition, NMR self-diffusion studies were conducted and revealed a bicontinuous microstructure of the investigated microemulsions. The skin penetration results are in good agreement with the obtained (19) F NMR self-diffusion coefficients of the active compounds in the microemulsion systems.

Finite dose skin mass balance including the lateral part: comparison between experiment, pharmacokinetic modeling and diffusion models.

This work investigates in vitro finite dose skin absorption of the model compounds flufenamic acid and caffeine experimentally and mathematically. The mass balance in different skin compartments (donor, stratum corneum (SC), deeper skin layers (DSL), lateral skin parts and acceptor) is analyzed as a function of time. For both substances high amounts were found in the lateral skin compartment after 6h of incubation, which emphasizes not to elide these parts in the modeling. Here, three different mathematical models were investigated and tested with the experimental data: a pharmacokinetic model (PK), a detailed microscopic two-dimensional diffusion model (MICRO) and a macroscopic homogenized diffusion model (MACRO). While the PK model was fitted to the experimental data, the MICRO and the MACRO models employed input parameters derived from infinite dose studies to predict the underlying diffusion process. All models could satisfyingly predict or describe the experimental data. The PK model and MACRO model also feature the lateral parts.

Natural microemulsions: formulation design and skin interaction.

Microemulsions are thermodynamically stable, colloidal drug delivery systems. This study presents the first substantiated comparison of natural, skin-compatible and biodegradable surfactants in terms of their suitability to form isotropic microemulsions and their skin interaction. Pseudoternery phase diagrams were constructed for lecithin, sucrose laurate and alkylpolyglycoside as single surfactants. Moreover, also mixed surfactant films of lecithin and alkylpolyglycoside as well as lecithin and sucrose laurate were tested. Large isotropic areas could be identified for lecithin, sucrose laurate and lecithin-sucrose laurate. One defined composition was chosen from the pseudoternery phase diagram, prepared with all investigated surfactants and 1:1 surfactant mixtures, respectively, and analysed for their effect on the stratum corneum on a molecular level by ATR-FTIR. Significantly higher frequency values of the symmetric and asymmetric CH(2)-stretching bands compared to the control were recorded for all microemulsions, indicating a hexagonal arrangement of the lipid chains. A similar trend was observed for the lateral packing of the alkyl chains as suggested by the shift of the CH(2)-scissoring bands. Moreover, diffusion cell experiments using porcine skin were performed with the two model drugs flufenamic acid and fluconazole. In both cases, the lecithin-based microemulsions showed the highest permeation rates followed by the alkylpolyglycoside-lecithin microemulsions.

Influence of the application area on finite dose permeation in relation to drug type applied.

For finite dose skin absorption experiments, a homogeneous donor distribution over the skin surface is usually assumed. However, the influence of the surface distribution on skin absorption is still unknown. The aim of this study was to evaluate the influence of the application area on the permeation of drugs during finite dose skin absorption experiments in static Franz diffusion cells. Permeation experiments with stained aqueous drug formulations were conducted, and the application area was determined by a suitable, objective, automated computational approach. The permeation of caffeine is strongly dependent on the application area. The variability between single experiments decreased when including the application area. For the lipophilic flufenamic acid, this was not the case. The variability highly increased after inclusion of the application area. Thus, a correction of the area is misleading. In summary, depending on the drug's physicochemical characteristics, the application area may influence skin absorption.

Evaluation of dextran-flufenamic acid ester as a polymeric colon-specific prodrug of flufenamic acid, an anti-inflammatory drug, for chronotherapy.

Dextran-flufenamic acid ester (Dex-FFA) with varied degree of substitution (DS) was prepared by imidazolide method. Dex-FFA was stable in pH 1.2 or pH 6.8 buffer. The depolymerization degree of Dex-FFA by dextranase decreased as DS increased. Dex-FFA with DS of 13 or 20 released FFA up to 70% or 21% of the dose, respectively, on 24 h-incubation with the 10% cecal contents. FFA was liberated up to 29% of the dose on 24 h-incubation of dextranase pre-treated Dex-FFA with the homogenates of the upper intestine, whereas no FFA was detected devoid of dextranse-pretreatment. Upon oral administration of Dex-FFA (DS 13, 20 mg equivalent of FFA/kg) or FFA (10 mg/kg) to rats, t(max) for FFA with Dex-FFA administration delayed approximately 6 h compared with that of free FFA administration, while C(max) for FFA was similar. The plasma level for FFA became greater around 6 h after administration of Dex-FFA than free FFA and it was maintained throughout the period of 24 h-experiment. Dex-FFA markedly attenuated gastric ulcerogenicity of FFA. Taken together, Dex-FFA could be useful as a colon-specific prodrug which possesses anti-inflammatory properties and offers opportunities as a chronotherapeutic approach for the treatment of arthritis.

The role of corneocytes in skin transport revised--a combined computational and experimental approach.

PURPOSE: To investigate mechanisms of compound-corneocyte interactions in a combined experimental and theoretical approach. MATERIALS AND METHODS: Experimental methods are presented to investigate compound-corneocyte interactions in terms of dissolution within water of hydration and protein binding and to quantify the extent of the concurrent mechanisms. Results are presented for three compounds: caffeine, flufenamic acid, and testosterone. Two compartmental stratum corneum models M1 and M2 are formulated based on experimentally determined input parameters describing the affinity to lipid, proteins and water. M1 features a homogeneous protein compartment and considers protein interactions only via intra-corneocyte water. In M2 the protein compartment is sub-divided into a cornified envelope compartment interacting with inter-cellular lipids and a keratin compartment interacting with water. RESULTS: For the non-protein binding caffeine the impact of the aqueous compartment on stratum corneum partitioning is overestimated but is successfully modeled after introducing a bound water fraction that is non-accessible for compound dissolution. For lipophilic, keratin binding compounds (flufenamic acid, testosterone) only M2 correctly predicts a concentration dependence of stratum corneum partition coefficients. CONCLUSIONS: Lipophilic and hydrophilic compounds interact with corneocytes. Interactions of lipophilic compounds are probably confined to the corneocyte surface. Interactions with intracellular keratin may be limited by their low aqueous solubility.

Influence of human skin specimens consisting of different skin layers on the result of in vitro permeation experiments.

The literature exhibits high variation in results from drug permeation experiments across human skin. Our purpose was to investigate the influence of human skin specimens, consisting of different skin layers and resulting from different skin preparation techniques, on the in vitro permeation of a model drug, i.e. flufenamic acid (FFA). FFA permeation across human (1) trypsin-isolated stratum corneum, (2) heat-separated epidermis and (3) dermis, (4) dermatomized skin and (5) full-thickness skin (FTS) from either a hydrophilic or lipophilic donor was investigated in Franz-type diffusion cells. Cumulative permeated drug amounts were plotted versus time, and a fit to Fick's 2nd law of diffusion was performed. Since performing skin diffusion experiments in the laboratory is time consuming and expensive, especially when using FTS, we also investigated the possibility of calculating the resistances of composite skin layers from the diffusion resistances of the individual skin layers. Due to short lag time, practical handling and economic preparation, heat-separated epidermis appears to be superior in human skin in vitro permeation experiments compared to separated stratumcorneum sheets, dermatomized skin and FTS. Furthermore, we found a good correlation between calculated and experimental resistances which underlines that calculation of the total diffusion resistance of composed skin preparations from resistances of individual skin layers is legitimate and useful. Considering our findings, improved interpretation of literature data and more consistent results for future permeation experiments are possible.

In-silico model of skin penetration based on experimentally determined input parameters. Part I: experimental determination of partition and diffusion coefficients.

Mathematical modeling of skin transport is considered a valuable alternative of in-vitro and in-vivo investigations especially considering ethical and economical questions. Mechanistic diffusion models describe skin transport by solving Fick's 2nd law of diffusion in time and space; however models relying entirely on a consistent experimental data set are missing. For a two-dimensional model membrane consisting of a biphasic stratum corneum (SC) and a homogeneous epidermal/dermal compartment (DSL) methods are presented to determine all relevant input parameters. The data were generated for flufenamic acid (M(W) 281.24g/mol; logK(Oct/H2O) 4.8; pK(a) 3.9) and caffeine (M(W) 194.2g/mol; logK(Oct/H2O) -0.083; pK(a) 1.39) using female abdominal skin. K(lip/don) (lipid-donor partition coefficient) was determined in equilibration experiments with human SC lipids. K(cor/lip) (corneocyte-lipid) and K(DSL/lip) (DSL-lipid) were derived from easily available experimental data, i.e. K(SC/don) (SC-donor), K(lip/don) and K(SC/DSL) (SC-DSL) considering realistic volume fractions of the lipid and corneocyte phases. Lipid and DSL diffusion coefficients D(lip) and D(DSL) were calculated based on steady state flux. The corneocyte diffusion coefficient D(cor) is not accessible experimentally and needs to be estimated by simulation. Based on these results time-dependent stratum corneum concentration-depth profiles were simulated and compared to experimental profiles in an accompanying study.

Determination of degradation pathways and kinetics of acyl glucuronides by NMR spectroscopy.

Acyl glucuronides have been implicated in the toxicity of many xenobiotics and marketed drugs. These toxicities are hypothesized to be a consequence of covalent binding of the reactive forms of the acyl glucuronide to proteins. Reactive intermediates of the acyl glucuronide arise from the migration of the aglycone leading to other positional and stereoisomers under physiological conditions. In order to screen for the potential liabilities of these metabolites during the early phase of pharmaceutical development, an NMR method based on the disappearance of the anomeric resonance of the O-1-acyl glucuronide was used to monitor the degradation kinetics of 11 structurally diverse acyl glucuronides, including those produced from the known nonsteroidal anti-inflammatory drugs (NSAIDs). The acyl glucuronides were either chemically synthesized or were isolated from biological matrices (bile, urine, and liver microsomal extracts). The half-lives attained utilizing this method were found to be comparable to those reported in the literature. NMR analysis also enabled the delineation of the two possible pathways of degradation: acyl migration and hydrolytic cleavage. The previously characterized 1H resonances of acyl migrated products are quite distinguishable from those that arise from hydrolysis. The NMR method described here could be used to rank order acyl glucuronide forming discovery compounds based on the potential reactivity of the conjugates and their routes of decomposition under physiological conditions. Furthermore, we have shown that in vitro systems such as liver microsomal preparations can be used to generate sufficient quantities of acyl glucuronides from early discovery compounds for NMR characterization. This is particularly important, as we often have limited supply of early discovery compounds to conduct in vivo studies to generate sufficient quantities of acyl glucuronides for further characterization.

Effect of selected fluorinated drugs in a "ringing" gel on rheological behaviour and skin permeation.

The purpose of the present study was to investigate the influence of different drugs exhibiting different solubility on the viscoelastic properties and on the skin diffusion profile of a ringing gel. In a preliminary rheology study with the placebo gel predominating elastic properties were confirmed and a temperature influence was indicated. Fluconazole, fludrocortisone-acetate, flumethasone-pivalate, flutamide and flufenamic-acid each 1% (w/w) were incorporated into the preparation and oscillatory measurements were performed at temperatures of 25, 28, 32 and 37 degrees C. In all drug containing formulations a high elastic G' value predominated the viscous G'' value. The highest G' value could be obtained with the incorporated flumethasone-pivalate. Additionally in almost all cases the G' values decreased with increasing temperature compared to the placebo gel. Additionally in vitro standard diffusion experiments using Franz-type cells and porcine skin were performed. Following rank order of the cumulative drug release after 48 h was obtained: fluconazole>flufenamic-acid>flumethasone-pivalate>flutamide>fludrocortisone-acetate. Furthermore an excellent chemical stability of all incorporated drugs was confirmed over 10 weeks.

Influence of nanoencapsulation on human skin transport of flufenamic acid.

The effect of the inclusion of flufenamic acid in poly(lactide-co-glycolide) nanoparticles on the transport of flufenamic acid into excised human skin was investigated. Penetration and permeation data were acquired using two different in vitro test systems: the Saarbrucken penetration model, where the skin acts as its own receptor medium, and the Franz diffusion cell, where the receptor medium is a buffer solution. For the stratum corneum, no differences were found between nanoencapsulated and free drug. Drug accumulation in the deeper skin layers and drug transport across human epidermis were slightly delayed for the nanoencapsulated drug compared to the free drug after shorter incubation times (<12 h). In contrast, after longer incubation times (>12 h), the nanoencapsulated drug showed a statistically significantly enhanced transport and accumulation (p < 0.05). Additionally, nanoencapsulated flufenamic acid was visualized by multiphoton fluorescence microscopy. Particles were found homogeneously distributed on the skin surface and within the dermatoglyphs, but no nanoparticles were detected within or between the corneocytes.

Effects of various vehicles on the penetration of flufenamic acid into human skin.

The effect of various vehicles (polyacrylate gels and wool alcohol ointments) on the penetration of flufenamic acid into excised human skin was investigated. Physico-chemical properties of the formulations were examined and discussed. Penetration data was gathered using two different in vitro test systems: the Saarbruecken penetration model (SB-M) and the Franz diffusion cell (FD-C). With wool alcohol ointments, drug concentration in the formulation was the decisive parameter for drug liberation and penetration. The incorporation of water into wool alcohol ointment led to increased drug amounts within the deeper skin layers (DSL), especially after longer incubation times. The drug concentration within the stratum corneum (SC) was not influenced by the bleeding effect of lipophilic, liquid components of the various wool alcohol ointments. With polyacrylate gels different results for liberation and penetration were observed. These results could be related to the effects of the drug concentration within the formulation and the penetration enhancers incorporated into the gels. Especially the effects of penetration enhancers clearly illustrated that liberation experiments do not predict the situation in the skin, but make experiments with a biological barrier essential. The high water content of the gels led to hydration of the skin specimen for the SB-M and the FD-C and therefore, in contrast to previous findings, comparable data were obtained in the penetration studies with both models. Furthermore, the quasi steady-state drug amount in the SC could be calculated for all formulations using an equation derived from a Michaelis-Menten kinetics. The data from both test systems were linearly correlated to each other. In addition, a direct linear relationship between the SC drug amount and the drug amount in the DSL was found as long as the quasi steady-state drug amount in the SC was not reached. A combination of all results might offer the chance to reduce the costs and to simplify the development of a new drug formulation.

Correlation between stratum corneum/water-partition coefficient and amounts of flufenamic acid penetrated into the stratum corneum.

The stratum corneum of various donors differs in particular in the composition of the lipoidal phase. Considering the drug amounts penetrating into the stratum corneum a simple methodology to correlate these differences in the stratum corneum composition with the drug amounts detectable within the stratum corneum is desirable. Penetration experiments investigating several incubation times were carried out with three different skin flaps using the Saarbruecken penetration model and the lipophilic model drug flufenamic acid. The drug amounts within the stratum corneum were obtained with the tape-stripping technique, while the drug amounts present in the deeper skin layers were achieved by cryosectioning. The stratum corneum/water-partition coefficient was determined with the same three skin flaps to characterize the lipoidal stratum corneum phase in general, and the differences were attributed to the different amounts of ceramides and sterols. In addition, for the lipophilic drug flufenamic acid, a direct linear correlation was found between the stratum corneum/water-partition coefficients and the drug amounts penetrated into the stratum corneum for all investigated time intervals (correlation coefficients of r(30 min) = 0.998, r(60 min) = 0.998 and r(180 min) = 0.987). In contrast to the stratum corneum/water-partition coefficients, the determination of a corresponding relationship for the stratum corneum and the deeper skin layers failed due to the reason that steady-state conditions could not be achieved for the deeper skin layers during the investigated time intervals. In summary, the stratum corneum/water-partition coefficients offer the possibility to predict drug amounts within the stratum corneum of different donor skin flaps without a time consuming determination of the lipid composition of the stratum corneum.

Human skin penetration of flufenamic acid: in vivo/in vitro correlation (deeper skin layers) for skin samples from the same subject.

Previously, the interest in in vivo/in vitro correlations in the dermal field of research has increased steadily. Unfortunately, in most cases the skin from different human donors was taken for in vivo and in vitro experiments, which led to problems concerning the interindividual variability of the skin. Therefore, we established a methodology to utilize the same skin for both sets of data. In time dependency, drug amounts in the stratum corneum and the deeper skin layers were determined from eight donors using the same skin area for in vivo and the corresponding in vitro tests. Penetration experiments were carried out with the lipophilic drug flufenamic acid dissolved in wool alcohols ointment as the model formulation, which was administered to the skin under "infinite dose" conditions. At different time points prior to starting the surgery, the drug preparation was applied topically on the edges of the skin area, which was planned for excision using Finn chambers. After anesthetizing the patient and disinfecting the operation area, the incubated skin pieces were cut off first and immediately frozen to limit further drug diffusion. In vitro experiments were performed on the remaining skin flap, using two different test systems, a penetration and a permeation model. At the end of all experiments (in vivo and in vitro) the skin specimens were segmented horizontally and the drug was extracted and quantified. The in vivo and in vitro drug amounts in the stratum corneum and the deeper skin layers, respectively, were compared. The inevitable use of unknown volumes of disinfectant in vivo (medical reasons) might be the reason why a correlation failed for the stratum corneum. Nevertheless, for both in vitro test systems a direct linear correlation was found for the deeper skin layers, which showed slopes of a = 3.2272 +/- 0.3933 (penetration model vs in vivo) and a = 1.7776 +/- 0. 1926 (permeation model vs in vivo). This difference demonstrates the varying influence of the test systems and represents a factor about which in vivo and in vitro data are shifted against each other. As far as the model drug flufenamic acid is concerned, this methodology represents a tool to predict drug penetration into the deeper skin layers in vivo after carrying out corresponding in vitro experiments. Therefore, the potential is given to reduce the number of in vivo experiments, the risk for the volunteers, and the costs for the development of new drug preparations.