Distribution of salicylic acid in human stratum corneum following topical application in vivo: a comparison of six different formulations.

Distribution of salicylic acid in human stratum corneum from treatment of six different formulations was assessed by quantitation of drug content in sequentially tape-stripped stratum corneum after a single 2-h dose was applied unoccluded to skin on the ventral forearm of four female subjects. The profile and total amounts of stratum corneum removed in 20 tape-strips varied among different types of formulations. With or without normalization by the total stratum corneum weights removed, the extent of drug delivery to the stratum corneum decreased in the following order: SA (5%) > > SAC (10%), Duofilm (16.7%) > TSSS (2%) > SAO (10%), Salic (2.5%), the percentage in parentheses indicating the salicylic acid concentration in each formulation. The greatest topical bioavailability was observed for the alcoholic solution containing glycerol (SA). The 10% collodion formulation (SAC) was found to deliver an amount of salicylic acid into the stratum corneum 2-fold greater than 10% ointment formulation (SAO). Use of absorption ointment (TSSS) also increased the uptake of salicylic acid into the stratum corneum in comparison with formulations based on simple ointment (SAO) and oil in water (o/w) cream (Salic). The partitioning of salicylic acid from collodion formulations (SAC and Duofilm) appeared to be concentration-independent. The results of this study indicate that topical bioavailability of salicylic acid in the stratum corneum varies substantially among different formulations.     

Transdermal permeation-enhancing activivity ofN-adamantyln-alkanamides for ibuprofen in the rabbit

FourN-adamantyln-alkanamides were prepared by amide, condensation reaction between amantadine and n-alkanoic acid. Their enhancing activity on the penetration of ibuprofen through rabbit skin from petrolatum ointment was evaluated in in-vivo experiment. The experiments showed that the compounds have a strong transdermal penetration-enhancing activity, and their activities were comparable with that of Azone. The measurements of the fluorescence polarization of DPH-labelled DPPC liposomes showed that these compounds considerablly decreased the phase transition temperature of the liposomes. The mechanism of the transdermal penetration-enhancing activity of the compounds was ascribed to the reduction of the resisitance to drug flux of the stratum corneum lipid layers due to the loose packing of the layers when the bulk head group of the enhancers inserts into the layers.     

Transdermal drug delivery: penetration enhancement techniques

There is considerable interest in the skin as a site of drug application both for local and systemic effect. However, the skin, in particular the stratum corneum, poses a formidable barrier to drug penetration thereby limiting topical and transdermal bioavailability. Skin penetration enhancement techniques have been developed to improve bioavailability and increase the range of drugs for which topical and transdermal delivery is a viable option. This review describes enhancement techniques based on drug/vehicle optimisation such as drug selection, prodrugs and ion-pairs, supersaturated drug solutions, eutectic systems, complexation, liposomes, vesicles and particles. Enhancement via modification of the stratum corneum by hydration, chemical enhancers acting on the structure of the stratum corneum lipids and keratin, partitioning and solubility effects are also discussed. The mechanism of action of penetration enhancers and retarders and their potential for clinical application is described.     

Sonophoresis. I. The Use of High-Frequency Ultrasound to Enhance Transdermal Drug Delivery

Previous attempts to use ultrasound (1-MHz frequency and 1 to 3-W/cm² intensity) to enhance transdermal drug delivery (so-called sonophoresis) have produced inconsistent results. Theoretical analysis of ultrasound propagation in tissue predicts that higher-frequency ultrasound (>1 MHz) will increase the concentration of energy deposition in the stratum corneum (SC) (typically, the rate-limiting barrier to percutaneous penetration). This hypothesis was tested by comparing the passive transdermal delivery of salicylic acid with that under the influence of ultrasound at 2-, 10-, and 16-MHz frequency; measurements were performed in vivo in hairless guinea pigs. Total drug absorbed was quantified by determining the amount of salicylic acid (1) present in SC tape strips and (2) eliminated in urine. Sonophoresis for 20 min at 2 MHz caused no significant increase in salicylic acid delivery over passive diffusion; treatment with ultrasound at 10 and 16 MHz, on the other hand, significantly elevated salicylic acid transport, by 4-fold and 2.5-fold, respectively. Kinetic analysis of the sonophoretic data at 10 and 16 MHz also revealed that the diffusion lag time associated with transdermal drug delivery (TDD) was reduced. A shorter period (5 min) of sonophoresis again resulted in enhanced TDD (relative to the corresponding control) at the higher frequencies; the delivered dose, and the level of enhancement, however, were lower than those after the 20-min treatment. In a separate series of experiments, it was shown that (a) ultrasound did not alter the release kinetics of salicylic acid from the gel formulation used and (b) pretreatment of the skin with ultrasound at 10 and 16 MHz lowered skin barrier function such that the subsequent delivery of salicylic acid was enhanced compared to passive transport without sonophoresis pretreatment. It follows that the enhancing effect of sonophoresis is due to a direct effect of ultrasound on (presumably) the stratum corneum.     

Percutaneous absorptoin-enhancing activity of urea derivatives

The effect of urea and urea derivatives on the percutaneous absorption of salicylic acid and sodium salicylate through the skin of rabbit from petrolatum ointment was investigated. It was found that addition of urea or urea derivatives to the ointment base significantly increased the percutaneous absorption of the drugs in proportion to the concentration of the additive. The percutaneous absorption-enhancing activities of these compounds were that urea derivatives with the more and longer alkyl substituents showed the stronger activities. These activities of urea and urea derivatives were ascribed to the binding of these compounds with the lipids and proteins of the stratum corneum of the skin and the swelling of the tissues, which leads to the reduction of the barrier property of the layer. The preliminary skin irritation test showed that urea and urea derivatives were quite non-irritating to the skin. These results suggest that urea derivatives have a strong possibility to be developed as a percutaneous absorption enhancer.     

Examination of the mechanism of oleic acid-induced percutaneous penetration enhancement: an ultrastructural study

The epidermal permeability barrier appears to be regulated primarily by the lamellar arrangement of lipid bilayers between coneocytes of the stratum corneum and presents a significant barrier to the transdermal delivery of drugs. The aim of the present study was to investigate the effects of oleic acid on the ultrastructure of stratum corneum lipids in rat skin. Wistar rats were treated topically with 10% oleic acid/propylene glycol for 2 h, the structure of stratum corneum was examined by electron microscopy using osmium tetroxide or ruthenium tetroxide postfixation, and the epidermal barrier function was evaluated in a lanthanum tracer study. Ultrastructural examination revealed that there was a marked alteration in the stratum corneum and the tracer penetrated into the intercellular spaces of the stratum corneum after application of oleic acid. These results suggest that ruthenium tetroxide postfixation is a powerful tool for the study of the stratum corneum lipid structure. Oleic acid might increase the epidermal permeability through a mechanism involving the perturbation of stratum corneum lipid bilayers and lacunae formation to enhance transdermal drug delivery.     

Intradermal concentration of hydroquinone after application of hydroquinone ointments is higher than its cytotoxic concentration

Ointments of the skin depigmentation agent hydroquinone (HQ) have been prepared by extemporaneous nonsterile compounding in our hospital. The HQ ointments were highly effective in the treatment of various types of skin pigmentations; however, various problems have emerged including chromatic aberration of the ointments, a relatively large variability of efficacy, and mild topical side effects including irritation. In this paper, the cytotoxicity of HQ was assessed in vitro using rat skin fibroblasts as the concentration with 50% survival after 24 h exposure to be 16.5 microM. The intradermal concentrations at 2 h after application of the HQ ointments was also estimated to be 358 mM and 51.7 mM in stratum corneum and viable tissue (viable epidermis+dermis), respectively, by an in vitro rat skin permeation study with rat full-thickness abdominal skin and Franz-type diffusion cells. It was demonstrated that the intradermal concentration of HQ was much higher than that eliciting cytotoxicity, suggesting that the topical side effects after application of HQ ointment were due to the cytotoxicity of HQ.     

Release of corticoids from oleaginous ointment bases containing drug in suspension.

Simplified methods for studying the release of drugs suspended in oleaginous ointment bases were developed. These procedures were used in studying the release rates of two corticoids, fluocinonide and flucloronide, from white petrolatum and petrolatum containing various adjuvants. A practical method for measuring drug solubilities was developed and used in determining solubilities of these corticoids in ointment bases. When using physical data obtained from model ointments, the release rates of drugs from modified ointment bases were predicted. Comparisons of the observed and predicted rates from ointments containing hydrophobic adjuvants indicated the usefulness of the physical model approach in predicting the release rates. For ointments containing emulsifying agents, the simple model used did not provide useful predictions.     

Physically cross-linked chitosan hydrogels as topical vehicles for hydrophilic drugs

Physically cross-linked chitosan hydrogels with lauric, myristic, palmitic or stearic acid were prepared by freeze-drying and have been studied for topical use. This study selected propranolol hydrochloride as a hydrophilic model drug to design a transdermal delivery system. We evaluated the effect of the nature of the cross-linker on drug permeation through porcine skin and the main permeation parameters (diffusion coefficient, flux and lag time) were calculated. All the chitosan hydrogels analysed provided more transcutaneous permeation of propranolol hydrochloride than the corresponding solution of the commercial drug. Among the different chitosan vehicles, chitosan-laurate and chitosan-myristate hydrogels enhanced lyophilised drug diffusion through the skin with respect to chitosan-palmitate and chitosan-stearate hydrogels. This can been explained by the interaction of the hydrogels with the stratum corneum, increasing the solubility of the drug in the skin.     

The transport effect of submicron emulsions on 5-flurouracil topical application

Water-in-oil submicron emulsions were used as carrier for the topical delivery of 5-fluorouracil (5FU). The effect of components such as level and hydrophilic–lipophilic balance (HLB) value of surfactant, type of cosurfactant, and drug concentration on the delivery capability of drug in the receptor fluid and in the various skin layers (stratum corneum, epidermis and dermis) were evaluated. The result showed the submicron emulsion could increase the transdermal and deposition of 5FU compared with the aqueous control. Submicron emulsion with surfactant at HLB of 6.0 had higher deposition amount of drug in epidermis layer. The deposition amount of drug in the skin layers increased with increased amounts of surfactant and drug loading of submicron emulsion. However, the 0.2% 5FU-load submicron emulsion showed a comparable deposition effect in various skin layers with the commercial product (5%, Efudix®), which indicated that the submicron emulsions could be a promising drug vehicle for topical application.     

Transdermal permeation-enhancing activities of some inorganic anions

Effects of sodium salts of various monovalent inorganic anions on transdermal permeation of salicylic acid were investigated. In in-vitro experiment using a Franz-type diffusion cell and excised mouse skin, the permeation-enhancing activities of the sodium salts of inorganic anions were roughly proportional to lyotropic Hofmeister swelling abilities of the anions; F^?<SO₄ ^2?<Cl^? <ClO₄ ^?<NO₃ <SCN^? <Br <I^?, i.e. l, Br and SCN increased the flux of drugs through the mouse skin, while F^?, SO₄ ^2?, Cl^?, ClO₄ ^? and NO₃ ^? decreased or did not affect the flux. In invivo experiment using the rabbit as the test animal, the plasma concentration of salicylic acid of the rabbit to which 10%-salicylic acid ointment containing 5%-Nal or NaBr was applied was significantly higher than that of the rabbit to which the ointment without the electrolytes was applied. The amounts of sterol leached out of stratum corneum sheet when the sheet was immersed in aqueous solutions of Nal, NaBr, or NaSCN were much more than that of stratum corneum immersed in aqueous solutions of the other inorganic anions. The FTIR/ATR spectroscopy showed that the peaks at 2853 cm^?1 and 2924 cm^?1 in the IR absorption spectrum of the stratum corneum sheet of the mouse were shifted to higher frequencies by the anions which enhanced the transdermal drug permeation, while not shifted by the anions which did not have any permeation-enhancing activities or have permeation-reducing activities. These results suggest that sodium salts of some anions such as iodide, bromide and thiocyanate enhance transdermal permeation of salicylic acid through swelling and perturbation of the skin structure by these anions.     

Liposomes and niosomes as topical drug delivery systems

The skin acts as a major target as well as a principle barrier for topical/transdermal (TT) drug delivery. The stratum corneum plays a crucial role in barrier function for TT drug delivery. Despite major research and development efforts in TT systems and the advantages of these routes, low stratum corneum permeability limits the usefulness of topical drug delivery. To overcome this, methods have been assessed to increase permeation. One controversial method is the use of vesicular systems, such as liposomes and niosomes, whose effectiveness depends on their physicochemical properties. This review focuses on the effect of liposomes and niosomes on enhancing drug penetration, and defines the effect of composition, size and type of the vesicular system on TT delivery.     

Transdermal iontophoresis. Part I: Basic principles and considerations.

The skin has increasingly become a route for the delivery of drugs with a range of compounds being considered for transdermal delivery generating a great deal of interest in this area of research. The passive delivery of most compounds across the skin is limited due to the barrier properties afforded by stratum corneum, the outermost layer of the skin. Transdermal iontophoresis is an effective technique for physically facilitating the transport of permeants across the skin by using electromotive force. It is being extensively explored as a potential means for delivery of hydrophilic, large and charged molecules and is also believed to be a future method of choice for peptides and proteins. In this context, this review focuses mainly on the basic principles and considerations of transdermal iontophoresis with particular emphasis on modeling, devices and parameters influencing transdermal iontophoresis.     

Strategies for overcoming the stratum corneum

Transdermal drug delivery has many advantages over the oral administration of drugs. This is the reason why many researchers have extensively investigated the transdermal absorption of drugs. However, a much smaller number of drugs are marketed using this route of delivery, compared to oral dosage forms, because drug absorption across the skin is very low due to the stratum corneum (the main barrier for drug absorption across the skin). Overcoming the penetration barrier would significantly improve the development of an efficient transdermal drug delivery system. Several techniques have been developed, or are under development, to bypass the stratum corneum. Approaches that have been made to overcome the stratum corneum fit into five different categories: (i) device and formulation; (ii) modification of stratum corneum by chemical enhancers; (iii) ablation; (iv) bypassing the stratum corneum via appendages; and (v) electrically assisted methods such as iontophoresis and electroporation. Furthermore, possible combinatorial uses of several approaches have been studied. Although the safety issues of these synergistic approaches still require clarification, several combinations could be promising. Finally, there is a necessity to regulate the intradermal disposition of drugs to develop a more efficient transdermal drug delivery system after overcoming the skin barrier.     

Permeation enhancer dodecyl 6-(dimethylamino)hexanoate increases transdermal and topical delivery of adefovir: Influence of pH, ion-pairing and skin species

Adefovir (9-(2-phosphonomethoxyethyl)adenine) is an acyclic nucleoside phosphonate currently used for the treatment of hepatitis B. The aim of this study was to evaluate the effect of permeation enhancer DDAK (6-dimethylaminohexanoic acid dodecyl ester) on the transdermal and topical delivery of adefovir. In porcine skin, DDAK enhanced adefovir flux 42 times with maximum at pH 5.8 suggesting ion pair formation. DDAK increased thermodynamic activity and stratum corneum/vehicle distribution coefficient of adefovir, as well as it directly decreased the skin barrier resistance. Maximal flux was observed already at 2% adefovir + 1% DDAK. The results were confirmed in freshly excised human skin where DDAK enhanced adefovir flux 179 times to 8.9 μg/cm²/h. This rate of percutaneous absorption would allow for reaching effective plasma concentrations. After the topical application, adefovir concentrated in the stratum corneum with low penetration into the deeper skin layers from either aqueous or isopropyl myristate vehicle without the enhancer. With 1% DDAK, adefovir concentrations in the viable epidermis and dermis were 33–61 times higher. These results offer an attractive alternative to established routes of administration of adefovir and other acyclic nucleoside phosphonates.     

固体脂质纳米粒作为水杨酸经皮给药载体的研究

目的 考察固体脂质纳米粒作为经皮给药载体对水杨酸经皮吸收的促渗透作用.方法 采用薄膜超声法制备水杨酸固体脂质纳米粒,以改良的Franz扩散池考察其体外透皮特性;并与水杨酸软膏剂比较,考察其促渗作用.结果 制备的水杨酸固体脂质纳米粒均匀圆整,包封率为46.4%,体外透皮特性优于普通软膏剂,24 h后皮肤药物累积透过量为654.3 μg/cm2,皮肤中药物残留量为22.99 μg,均分别显署高于软膏剂组(128.0 μg/cm2和0.84 μg,P<0.05).结论 固体脂质纳米粒作为水杨酸经皮给药载体,可有效促进药物透皮吸收和增加药物在皮肤中储留量,而且可延缓药物的释放,从而有效提高药物疗效及患者依从性.     

Feasibility of Measuring the Bioavailability of Topical Betamethasone Dipropionate in Commercial Formulations Using Drug Content in Skin and a Skin Blanching Bioassay

An in vivo technique has been developed which simultaneously compares a skin blanching bioassay with drug content in human stratum corneum following topical application of four 0.05% beta-methasone dipropionate formulations. Bioavailability of drug from commercial cream and ointment formulations was assessed by quantification of drug content in tape-stripped stratum corneum and skin blanching in the treated skin site under occluded conditions. Tape-stripping removed stratum corneum to a varying degree between individuals but was consistent (35%) within an individual with all formulations, day to day. A correlation (r = 0.9935) between the amount of drug in the treated stratum corneum normalized for surface area and the corresponding skin blanching score was observed with four 0.05% betamethasone dipropionate formulations. Increasing the amount of drug in the tape-stripped stratum corneum correlated with an increased skin blanching score. Ointment formulations delivered more drug to the skin and produced greater blanching scores than the cream formulations. Topical corticosteroid content in the treated skin site can therefore be quantified and correlates well with the resulting pharmacodynamic activity.     

Novel penetration enhancers for skin applications: a review

The use of topical formulation is popular over the past decade due to extensive researches made in the field of transdermal drug delivery. As a result, an increasing number of drugs are being added to the list of therapeutic agents that can be delivered to systemic circulation through the skin. Commonly available dosage forms for the topical application are creams, ointments, gels, patches etc. The therapeutic benefits of the above topical formulations are limited due to barrier property of stratum corneum (SC). The use of chemical penetration enhancers (CPEs) is one of the long standing approach to overcome the barrier property of SC. Numerous class of novel compounds have been evaluated for penetration enhancement activity, including soft enhancement for percutaneous absorption (SEPA), for example, 2 N-nonyl-1,3- dioxolanes, N-acetyle prolinate esters (such as pentyl- and octyl-N-acetyle prolinate), alkyldiloxanes (e.g., 1-Alkyl-3-b-D glucopyranosyl-1,1,3,3-tetramethyl disiloxanes), transcarbam (such as 5-(dodecyloxycarbonyl) pentylammonium-5- (dodecyloxycarbonyl) pentylcarbamate), iminosulfurane (like N-hexyl,N-benzoyl-S,S-dimethylimino-sulfuranes), capsaicin derivatives (e.g., Nonivamide), cinnamene compounds (such as cinnamic acid, cinnamaldehyde etc), terpenes (like clove and basil oil) and synergestic combination of penetration enhancers (SCOPE). We briefly describe about the anatomy of skin. Potential mechanisms of action of above novel PEs along with adverse reactions associated with traditional PEs are also considered in this review.     

Permeation enhancer dodecyl 6-(dimethylamino)hexanoate increases transdermal and topical delivery of adefovir: Influence of pH,ion-pairing and skin species

Adefovir (9-(2-phosphonomethoxyethyl)adenine) is an acyclic nucleoside phosphonate currently used for the treatment of hepatitis B. The aim of this study was to evaluate the effect of permeation enhancer DDAK (6-dimethylaminohexanoic acid dodecyl ester) on the transdermal and topical delivery of adefovir. In porcine skin, DDAK enhanced adefovir flux 42 times with maximum at pH 5.8 suggesting ion pair formation. DDAK increased thermodynamic activity and stratum corneum/vehicle distribution coefficient of adefovir, as well as it directly decreased the skin barrier resistance. Maximal flux was observed already at 2% adefovir + 1% DDAK. The results were confirmed in freshly excised human skin where DDAK enhanced adefovir flux 179 times to 8.9 μg/cm²/h. This rate of percutaneous absorption would allow for reaching effective plasma concentrations. After the topical application, adefovir concentrated in the stratum corneum with low penetration into the deeper skin layers from either aqueous or isopropyl myristate vehicle without the enhancer. With 1% DDAK, adefovir concentrations in the viable epidermis and dermis were 33–61 times higher. These results offer an attractive alternative to established routes of administration of adefovir and other acyclic nucleoside phosphonates.     

Role of stratum corneum lipid fluidity in transdermal drug flux

Fatty acids are effective penetration enhancers for the transdermal delivery of certain co-applied drugs. In order to assess the mechanism of enhancement, spectrometric, calorimetric, and flux techniques were used to study porcine stratum corneum following treatment with a series of cis- and trans-positional isomers of octadecenoic acid. Results obtained from spectrometric and calorimetric measurements show increased lipid fluidity following treatment of the stratum corneum with the cis monoenoic acids which have the site of unsaturation centrally located. Under similar conditions, these same cis monounsaturated acids resulted in enhancement of salicyclic acid flux through porcine skin. The striking parallelism between flux and fluidity measurements suggests that transdermal drug flux may be ultimately related to stratum corneum lipid structure.