Permeation of Cs+ ions across skin barriers

Permeation of metal Cs⁺ ions from water solutions across the intact, stripped and splitted skin of 5- or 9-day old rat was studiedin vitro using vertical diffusion cells. The results showed that the stratum corneum (horny layer) of this new animal skin model represents the principal pentration barrier. The relative importance of the percutaneous absorption of Cs⁺ ions through transepidermal and transfolicular routes has been assessed comparing the penetration across skin without hairs and skin just haired. The results have shown that the shunt diffusion along hair follicles can be of preponderant value.     

Transfer of Radionuclides Across Skin Barriers of Animal Skin Models in Vitro

Radioactive skin contamination with radionuclides in ionic forms after the permeation across skin models was studied in vitro. Using animal skin models of 5-day-old rat and 9-day-old rat, either intact or stripped, it was found that besides the transepidermal also the transfolicular flux can be important. Stratum corneum was found to be the principal permeation barrier in all cases. The study of penetration — time profiles revealed that permeated amounts were proportional to time in the case of ¹³⁷Cs⁺ and ⁶⁰Co²⁺, but they showed a local maximum in the case of ¹⁴⁷Pm³⁺.     

Penetration of radionuclides across the skin: Concentration dependence of60Co permeation

Co²⁺ ion penetration at different concentrations across animal models of human skin-five days old rat skin (without hairs) and nine days old rat skin (with hairs)—was studied in vitro in vertical diffusion cells. The results showed that the permeated amounts of Co²⁺ ions are proportional to its concentration in donor solutions, whereby permeated fractions are higher at lower concentrations. Results confirmed that the most important barrier against the penetration of ions is horny layer of the skin.     

Penetration of radionuclides across the skin: Glucans as possible inhibitors of metals permeation

Penetration of Cs⁺ , Cd ²⁺ and Co²⁺ions across an animal model of human skin (five-day-old rat skin) was studiedin vitro in vertical diffusion cells. Glucans (fibrilary beta-glucan, carboxymethyl-chitosan-glucan)were used as permeation inhibitors with the aim to reduce the potential toxicologicaleffect of these metals in humans. Of the glucans studied, carboxymethyl-chitosan-glucanwas the more effective inhibitor. The dose-dependency of this effect was demonstrated.     

Enhanced skin permeation of diclofenac by ion-pair formation and further enhancement by microemulsion

Enhancement of skin permeability of anionic diclofenac from non-aqueous vehicle isopropyl myristate (IPM) by ion-pair formation with either alkylamines or benzylamine as model cationic ions was examined in guinea pig dorsal skin. Diclofenac ion flux increased in the presence of these amines due to an increase in solubility. Maximum flux was observed in the presence of n-hexylamine, which induced 7.3-fold increase accompanied by a 45-fold increase in solubility. Permeability coefficients of the ionic form of diclofenac in the presence of benzylamine, n-hexylamine and iso-octylamine as counter ions in IPM were larger than those of the non-ionic form of diclofenac. Since the solubility of diclofenac was still limited, to obtain further enhancement of skin permeation, the effects of microemulsions as a vehicle consisting of phosphate buffered saline (PBS), isopropyl myristate (IPM), polyoxyethylene sorbitan monooleate (Tween 80) and ethanol were examined for transport of diclofenac-benzylamine ion-pairs. All microemulsion formulations tested increased diclofenac flux 4.9-fold to 10.7-fold over the value without a microemulsion accompanied by a 217-fold to 302-fold improvement in the solubility of diclofenac-benzylamine ion-pairs, but permeability coefficients were decreased 28-44 fold. Maximum enhancement was observed for a microemulsion with a ratio of PBS, IPM, ethanol and Tween 80 of 25 : 8 : 47 : 20 (w/w). The present findings suggest the usefulness of combined use of ion-pairs with microemulsions for enhancement of skin permeation of ionic drugs.     

Acrylate terpolymer in fabrication of medicated skin patches

An acrylate based pressure sensitive adhesive (PSA) was synthesized to design a drug‐in‐adhesive (DIA) type transdermal therapeutic system (TTS) for nitroglycerin used in the treatment of angina pectoris. 2‐Ethylhexyl acrylate (EHA), methyl methacrylate (MMA) and acrylic acid (AA) were used to synthesize the PSA by free radical solution polymerization. The effects of reaction time, reaction temperature, initiator concentration and solvent on polymerization were studied. The synthesized terpolymer was characterized by ¹H‐NMR, FT‐IR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) and also evaluated for intrinsic viscosity, refractive index, peel strength, moisture uptake and skin irritation potential. The PSA was used to develop DIA type patches of nitroglycerin. The patches were cast using solvent evaporation technique and dried at controlled temperature. The patches were evaluated for thickness uniformity, weight variation, peel strength and moisture pick‐up. The percent drug content and in vitro drug release was determined by high pressure liquid chromatography (HPLC) method. On the basis of in vitro release profile, patches were selected for in vitro skin permeation studies. The developed formulation TP‐1 (K = 24.892 mcg/cm²/hr) followed zero‐order rate kinetics and showed better skin permeation rate in comparison to the marketed TTS (MTTS) (K = 17.413 mcg/cm²/hr). TP‐1 was subjected to stability testing for a period of 1 year according to ICH guidelines. The patches were found to be stable and an expiry date of 2 years was predicted with storage at 25 °C or below. Copyright © 2001 John Wiley & Sons, Ltd.     

Binding heavy metal ions with polymerized onion skin

Red onion skin is highly effective for binding heavy metal ions from aqueous solutions. Color leaching can be prevented and the physical characteristics of the substrate can be improved by treatment with formaldehyde in an acidic medium. Batch and column experiments have been conducted with Cu²⁺, Cd²⁺, Zn²⁺, Ni²⁺, Hg²⁺, and Pb²⁺. Almost quantitative removal of the metal ions from solution can be achieved by using columns of the treated onion skin. Competition of the various metal ions for the substrate has been investigated. The capacity of the substrate in the majority of the metal ions studied is well above 1 meq/g. The use of polymerized onion skin to remove heavy metal ions from domestic and industrial wastewater to safe levels has been recommended as a cheap and effective alternative for commercial ion-exchange resins.     

Calculation of skin permeability coefficient for ionized and unionized species of indomethacin.

The contribution of ionized and unionized species to the overall permeation of weak electrolytes through the skin was investigated to determine the effect of pH in the vehicle on the permeability of indomethacin (IDM), as a model drug, through hairless rat skin. The permeability of IDM through polydimethylsiloxane (silicone) and poly(2-hydroxyethyl methacrylate) (pHEMA) membranes which may reflect lipid and aqueous pathway, respectively, was also measured for comparison. As the pH in the vehicle increased, there was an exponential increase in the skin permeation rate of IDM. The permeation rate of IDM through the silicone membrane was constant independent of pH, whereas that through the pHEMA membrane increased with increasing pH, similar to the skin permeation. The permeability coefficients of ionized and unionized species through the skin estimated using the skin permeation rates and solubilities of IDM at various pHs were 1.50 x 10(-7) and 2.79 x 10(-5) cm/s, respectively. These results indicated that the permeation of ionized species greatly contributed to the total permeation of IDM at higher pH, and that the total permeation rate of IDM was determined by the permeation of unionized species at lower pH. These contributions depend on the pH and pKa values and the ratio of permeability coefficient of each species. It was also confirmed that the skin has at least two kinds of permeation pathways and these two species permeate through a different pathway.     

Development and validation of an analytical method for the quantification of cytochrome c in skin transport studies

A simple isocratic HPLC method for the quantification of Cytochrome c in skin permeation samples was developed and validated. The mobile phase comprised a 41 : 59 mixture of an organic phase A (0.1% trifluoroacetic acid in a 90 : 10 mixture of MeCN–H₂O) and an aqueous phase B (0.1% trifluoroacetic acid in H₂O). The Cytochrome c retention and run times were 2.62 and 8.0 min, respectively—much shorter than those for existing gradient methods. The response was accurate, precise and linear from 2.5 to 25 μg/mL. The mean recoveries for intra‐day and inter‐day analysis ranged from 88.5 to 103.8% and the RSD varied from 0.05 to 1.55%. The assay was used to quantify transport of Cytochrome c across intact and laser‐microporated porcine skin in vitro. Cytochrome c permeation and the amount of protein retained within the membrane over 24 h were quantified as a function of the number of micropores. Although no Cytochrome c permeation was observed across intact skin, laser microporation enabled delivery of 22.9 ± 3.3 and 56.0 ± 15.9 μg/cm² of the protein across skin samples with 300 and 1800 micropores, respectively. In conclusion, the HPLC method provided a fast, efficient means to quantify Cytochrome c in samples from skin transport studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Enhanced skin permeation of cationic drug ketotifen through excised guinea pig dorsal skin by surfactants with different electric charges

Using excised guinea pig dorsal skin, we examined the effects of three surfactants, anionic sodium dodecylsulfate (SDS), cationic n-dodecyltrimethylammonium bromide and non-ionic n-dodecyl-beta-D-maltoside, all of which commonly have an n-dodecyl group, on in vitro skin permeation of the cationic drug ketotifen. All these three surfactants increased the skin permeation of ketotifen. Among the surfactants tested, anionic SDS had the largest enhancement effects, and significantly increased the permeation at concentrations over 1 mM. The enhancement effect of the same anionic surfactant on the permeation of anionic salicylate was smaller and similar to that of cationic n-dodecyltrimethylammonium. The enhancement effects of SDS on ketotifen permeation were more marked than those of the cationic surfactant but differed from previous findings of their effects on other drugs permeation. Analysis of the retention of ketotifen in the skin suggested that SDS-induced increase in the transfer of hydrophilic ketotifen to the skin is the main reason for the marked increase in skin permeation.     

Diffusion potential is induced by coupled transport of ions through liquid membrane: nonlinear response to pH change in a reverse permeation system

In a cation exchange liquid membrane-aqueous alkali metal chloride system, diffusional flux of alkali metal ion driven by proton was observed. A supported liquid membrane formed on a Teflon filter by impregnating it with stearic acid-doped 1-octanol was used. The internal aqueous phase contained KCl and HCl, and the external aqueous phase also contained KCl. The initial concentrations of K⁺ ions of both phases were 1×10⁻¹ mol dm⁻³ for all the measurements. The concentration of HCl in the internal solution was kept at 1×10⁻² mol dm⁻³. The pH of the external solution was changed successively with HCl, appropriate buffer solution, or KOH. The pH dependence of membrane potential showed hysteresis loop in the range from neutral to alkaline pH, where reverse ion permeation was observed after the flux had been measured in the system with the external solution of an alkaline pH (pH 13). In the acidic range below neutral pH, the hysteresis of the membrane potential as well as reverse ion permeation was not observed. To elucidate the correlation between the appearance of hysteresis loop and the reverse ion permeation driven by proton across the membrane, the time course of the membrane potential in response to pH change was investigated. In the pH range where reverse permeation phenomena appeared, the time dependence of the membrane potential in nonsteady-state showed biphasic behavior. From the time course curve of the membrane potential, the total membrane potential was divided into the Donnan potential and the diffusion potential. From these findings, it was demonstrated that the diffusion potential was generated within the membrane only in the alkaline range where reverse ion permeation occurred. Analyzing the diffusional flux, the diffusion coefficient of potassium ion in the membrane was obtained taking the Donnan potential into account to be much greater than that in the membrane solvent. As a result of comparison of the diffusional fluxes measured by atomic absorption spectrometry and solution conductometry, the flux of the potassium ion was found to be significantly greater than that of the hydrogen ion in the opposite direction, especially at extremely high pH region. This implies the flows of hydroxide ions and neutralization reaction within the membrane facilitate the reverse ion permeation process of potassium ions.     

Prediction of skin permeability of drugs. I. Comparison with artificial membrane

In order to measure the contribution of lipid and pore (aqueous) pathways to the total skin permeation of drugs, and to establish a predictive method for the steady state permeation rate of drugs, the relationship between permeability through excised hairless rat skin and some physicochemical properties of several drugs were compared with those through polydimethylsiloxane (silicone) and poly(2-hydroxyethyl methacrylate) (pHEMA) membranes, as typical solution-diffusion and porous membranes, respectively. A linear relationship was found between the permeability coefficients of drugs for the silicone membrane and their octanol/water partition coefficients. For the pHEMA membrane, the permeability coefficients were almost constant independent of the partition coefficient. On the other hand, the skin permeation properties could be classified into two types: one involves the case of lipophilic drugs, where the permeability coefficient is correlated to the partition coefficient, similar to the silicone membrane; and the other involves hydrophilic drugs, where the permeability coefficients were almost constant, similar to pHEMA membrane. From the above results, the stratum corneum, the main barrier in skin, could be described as a membrane having two parallel permeation pathways: lipid and pore pathways. An equation for predicting the steady state permeation rate of drugs was derived based on this skin permeation model.     

Drug permeation through skin from matrix-type drug delivery systems

Nitroglycerin permeation through hairless mouse skin from various matrix-type transdermal delivery systems has been explained fairly well on the basis of a two-layer skin model. The diffusivity and solubility of the drug in the stratum corneum and in the viable skin have been calculated. The diffusivity in the stratum corneum was found to be affected by the type of delivery system, while that in the viable skin was hardly influenced by the delivery system. The loading dose, diffusivity and solubility of the drug in the delivery system were found to be the important design parameters for skin-control transdermal drug delivery and, therefore, the transdermal delivery system has to be optimized by controlling these three parameters to achieve a maximum rate of skin permeation with minimum drug loading dose.     

Influence of isosorbide dinitrate concentration on its skin permeability from adhesive matrix devices.

Adhesive matrix devices containing a model drug, isosorbide dinitrate (ISDN), were prepared with three different types of pressure sensitive adhesives (PSAs). ISDN permeation through excised hairless rat skin from the different devices was measured in vitro. For each PSA type, the steady state permeation rate of ISDN increased proportionally with an increase of ISDN concentration in the PSA and reached a maximum level at a certain concentration. Although the concentrations reaching the maximum skin permeation level varied among PSA types, the maximum rate for each PSA type was largely similar to that for ISDN aqueous suspension. The release rate of ISDN from devices was too fast to influence the skin permeation rate for all devices. In the PSA of devices showing maximum skin permeability, ISDN crystalline was observed by polarizing microscopy and differential scanning calorimetry. These results suggest that the skin permeation of ISDN from adhesive matrix devices was controlled by the thermodynamic activity of the drug in the PSAs.     

Effect of several enhancers on the skin permeation of water-soluble drugs

Since the percutaneous absorption rates of water-soluble drugs are low in general, an enhancing system is needed when using the skin as an administration site for the drugs. We have investigated the effect of various penetration enhancers on the in vitro and in vivo percutaneous absorptions of catecholamine analogs, i.e. levodopa (LD), dopamine hydrochloride (DPH) and isoproterenol hydrochloride (IPH), as model water-soluble drugs. It was found that medium-chain glycerides (Sefsol 318) markedly enhanced the in vitro permeation of the drugs through excised hairless rat skin among the enhancers tested in the present experiments; the permeation rates with 5% Sefsol 318 in water were about 65, 34 and 53 times higher than the corresponding control (without enhancer) for LD, DPH and IPH, respectively. In addition, the in vivo percutaneous absorption experiments showed that the blood levels of these drugs after application of aqueous gels containing 5% Sefsol 318 on rat skin were higher than those in the absence of enhancer. Drug levels in the liver and kidney were also higher than without Sefsol 318. Percutaneous administration of DPH with Sefsol 318 to hairless rats resulted in lower diastolic blood pressure and a slightly higher heart rate with as compared to administration without the enhancer. These results suggest that Sefsol 318 is a potential candidate to enhance the transdermal absorption of water-soluble drugs.     

A simple and rapid method to assess butenafine hydrochloride in skin samples and a comparative cutaneous retention study of two marketed formulations

A new method for the quantification of butenafine hydrochloride (BTF) present in the main skin layers was validated and a study conducted with the aim of analyzing the penetration and/or the permeation of the drug. The quantification was performed by liquid chromatography. To evaluate the specificity of the method, the influence of the components of the skin was analyzed, as well as the skin in contact with the excipient ingredients. Linearity was assessed with concentrations in the range of 0.1–10 μg/mL (r ² = 0.9999) and ANOVA showed non‐significant linear deviation (p > 0.05). Adequate results were obtained for repeatability, intra‐day precision and accuracy. The obtained values for the limit of quantification and the limit of detection were 68.4 and 17.7 ng/mL, respectively. Also, a comparative study of BTF cutaneous penetration through porcine skin was performed applying two different formulations: Tefin, present in the Brazilian market, and Lotrimin Ultra^®, available in the American market. No statistical difference was found in the skin (epidermis plus dermis) and in the epidermis (p > 0.05), although in the dermis the difference was significant (p < 0.05). During the experimental period (8 h), no drug permeation from either formulation was detected in the receptor fluid. Copyright © 2011 John Wiley & Sons, Ltd.     

An experimental approach to study the binding properties of vitamin E (alpha-tocopherol) during hairless mouse skin permeation.

An experimental approach to study the binding properties of vitamin E has been developed. Total vitamin E solubility in the skin was determined by a partition study, followed by in vitro skin permeation studies with whole skin and stripped skin. The amount of freely diffusable vitamin E in the diffusion process was determined from the permeation profiles of whole skin and stripped skin by employing a bi-layer model. The concentrations of vitamin E in the stratum corneum and viable dermis were determined separately. By subtracting this amount from the total concentration of vitamin E in the skin, as determined by the solubility study, the amount of bound vitamin E was determined. After skin permeation reached a steady state, the donor solution was removed and the permeation study continued (desorption study). During the entire period of the desorption experiment, the amount of vitamin E in the receptor solution hardly increased and remained constant. After the desorption experiment, vitamin E still remaining in the skin was determined by extracting with tissue solubilizer, SOLABLE, and is considered as the amount of vitamin E strongly bound in the skin. The concentrations of bound vitamin E determined by permeation and desorption studies coincided relatively well. To further investigate skin binding of vitamin E, a differential scanning calorimetry study was performed. Vitamin E-treated stratum corneum showed phase transitions at 76 and 85 degrees C, associated with lipid transitions. The thermal transitions associated with the lipid transition suggested interactions of vitamin E with lipid components of the skin. During skin permeation, vitamin E forms a very strong reservoir in the skin tissue and this amount of vitamin E, about 30%, exists as a bound-form with the lipid components of the stratum corneum.     

In vitro permeation of chromium species through porcine and human skin as determined by capillary electrophoresis–inductively coupled plasma–sector field mass spectrometry

Since the species that trigger chromium allergy are not yet known, it is important to gain more of an insight into the mechanism of chromium transport through the skin and into the relationship between chromium allergy and chromium species. In vitro permeation studies with porcine and human skin were performed using a Franz static diffusion cell. Investigations attempted to elucidate (i) which Cr compounds are able to permeate through skin, (ii) the influence the Cr concentration in the donor solution has on the Cr permeation, and (iii) the effect that the time of exposure to the donor solution has on Cr permeation. Capillary electrophoresis hyphenated to inductively coupled plasma–sector field mass spectrometry (CE–ICP–SFMS) was used to separate and quantify the Cr species in the receptor fluid. 50 mmol L⁻¹ phosphate buffer (pH 2.5) was used for CE separation, and two different electrophoretic runs were carried out (in the positive and negative modes). Pneumatic nebulization (PN)-ICP-SFMS was used in order to quantify the total amount of Cr absorbed by the skin after microwave-assisted acid digestion of the tissue. Cr(VI) was found to pass most easily through the skin. Nevertheless, Cr(VI) was also shown to be absorbed more efficiently by the skin than Cr(III), an observation attributed to a more pronounced rejection of the positively charged Cr(III) ions by the skin barrier. These results were in good agreement with in vitro permeation studies previously reported in the literature in which other analytical techniques were used. Differences observed in the permeation of Cr following the application of aqueous Cr donor solutions and Cr-containing simulated sweat donor solutions are also described.      

Development and validation of a simple method for the extraction and quantification of crisaborole in skin layers

Crisaborole is a boron compound recently approved by the US Food and Drug Administration as a 2% ointment for the treatment of mild to moderate atopic dermatitis. This work describes a simple method for the quantification of the drug in the skin layers at the end of in‐vitro permeation experiments. Chromatographic separation was carried out on a reverse‐phase C₁₈ column using a mixture of trifluoroacetic acid 0.05%–acetonitrile (55:45, v/v) as mobile phase, pumped at 1 ml/min. Column temperature was 35°C and UV detection was performed at 250 nm. The method was linear in the range of concentration from 0.06 to 6 μg/ml (R² = 1) and was selective, precise and accurate. Depending on the solvent used, the LOQ ranged from 0.014 to 0.030 μg/ml and the LOD from 0.005 to 0.010 μg/ml. The extraction from all the skin layers was quantitative. The developed method was successfully tested in an in‐vitro permeation study, proving to be an effective tool in the development of new formulations containing crisaborole.     

DSC measurements on full thickness mice skin

Highly lipophilic basic drugs, the antiestrogens AE1 and AE2 shall be delivered transdermally. DSC as an additional tool in combination with classic investigation techniques should be used to clarify permeation enhancement. Skin treatment with pure solvents, polyethyleneglycol (PG) and dimethylisosorbide (DMI), slightly changed the phase transition temperatures. Formulations containing lauric acid markedly shifted these transitions to lower temperatures, indicating a lipid-fluidising action of lauric acid. In those cases an additional endothermic peak was observed around 40°C, which is attributed to the melting of crystalline lauric acid. Since the DSC program started at -20°C, it is very likely that lauric acid in the skin samples crystallized. A formulation of polyethyleneglycol and lauric acid leads to significantly higher deposition of lauric acid into the skin, in opposition to dimethylisosorbide/lauric acid formulation. These findings correspond to the results from our in-vitro permeation studies, where a significantly higher transdermal steady-state flux of lauric acid from polyethyleneglycol-formulation in comparison to dimethylisosorbide-formulation was observed. By this unique combination of polyethyleneglycol and lauric acid, the barrier is obviously modified in a way, which allows the highly lipophilic antiestrogens to permeate easily through the skin. So, from this formulation steady-state fluxes of AE-1 were observed, representing approximately the same value compared to the unhindered permeation through skin without stratum corneum. The grade of temperature shift on the skin lipids to lower temperatures can be correlated with softening effects and the enhancement potential of the formulation. This revised version was published online in July 2006 with corrections to the Cover Date.