In Vitro Percutaneous Absorption of Arildone,a Highly Lipophilic Drug,and the Apparent No-Effect of the Penetration Enhancer Azone in Excised Human Skin

Purpose. Arildone, a novel lipophilic antiviral drug when evaluated in Clinical Trials showed limited skin absorption and antiviral efficacy. These studies were conducted to explain the apparent poor absorption characteristics and attempt to promote skin absorption by using Azone, a penetration enhancer. Methods. Standard in vitro skin permeation methods using excised human skin were employed to characterise the absorption of Arildone. ¹⁴C-Arildone was used to estimate the distribution in skin layers by scintigraphic and autoradiographic procedures. Results. The aqueous solubility and distribution constant values for Arildone were 2 µg ml^–1 and 5 × 10⁵ (isopropyl myristate/water), respectively. Absorption through full thickness skin or stratum corneum-viable epidermal membranes (diffusional resistant dermis removed), from a propylene glycol vehicle, was slow and the addition of Azone had no effect on the permeation rate. Distribution studies showed accumulation of Arildone in the stratum corneum. The concentration of Arildone in the viable epidermis was estimated from sectioning the skin and was found to be in sufficient amounts (400 µg cm^–3) to have potential antiviral activity. Conclusions. The apparent accumulation of Arildone in the stratum corneum suggested that the hydrophilic skin region presented the main barrier to permeation. Azone which affected the permeability of the stratum corneum was therefore not effective at enhancing Arildone absorption. Vehicles which readily permeate and enhance the transfer of lipophilic drugs from the stratum corneum into the viable epidermis were recommended.     

Percutaneous Absorption and Elimination of the Penetration Enhancer Azone in Humans

The percutaneous absorption and elimination of Azone, a new penetration enhancer, were investigated in humans. The distribution and accumulation of Azone in the skin were studied by means of tape stripping. These studies reveal that pure Azone is poorly absorbed. Furthermore, what little Azone is absorbed appears to be rapidly cleared from the circulation by the kidneys. In order to explain the urinary excretion profile, the formation of at least one metabolite is suggested. No accumulation of Azone in the skin was observed.     

In Vivo Evaluation of Acyclovir Prodrug Penetration and Metabolism Through Rat Skin Using a Diffusion/Bioconversion Model

Purpose. In order to evaluate the in vivo penetration of prodrugs which undergo metabolism in skin, we analyzed thein vivo penetration profiles of acyclovir prodrugs based on a two-layer skin diffusion model in consideration of metabolic process. Methods. Acyclovir prodrugs (e.g., valerate, isovalerate and pivarate) were used as model prodrugs and the amounts excreted in urine were measured after percutaneous application. In vivo penetration profiles were then estimated by employing a deconvolution method and the penetration of acyclovir prodrugs was analyzed using a diffusion model. Subsequently, diffusion, partitioning and metabolic parameters were compared under in vitro and in vivo conditions. Results. Although total penetration amounts at the end of the experiment were similar for the three prodrugs, the ratio of intact prodrug to total penetration amount differed significantly. Moreover, the excretion and absorption profiles were also very different for each prodrug. Enzymatic hydrolysis rate constants calculated under in vivo conditions were considerably larger than those obtained in the skin homogenate and in vitro penetration experiments. Conclusions. The present skin diffusion/bioconversion model combined with computer analysis enables us to comprehensively account for diffusion, partitioning and metabolism during in vivo percutaneous absorption. Nevertheless, different enzymatic hydrolysis rate constants obtained under bothin vivo and in vitro conditions demonstrate the difficulty of obtaining accurate values for in vivo enzymatic activity from related in vitro experiments.     

Effect of Vehicles and Penetration Enhancers on the In Vitro and In Vivo Percutaneous Absorption of Methotrexate and Edatrexate Through Hairless Mouse Skin

Purpose. Low-dose methotrexate (MTX) is approved for the treatment of recalcitrant rheumatoid arthritis (RA). The objective of this study was to determine the effect of vehicles and penetration enhancers on the percutaneous absorption of MTX and its analog edatrexate (EDAM), and develop transdermal (TD) delivery systems of the drugs for the treatment of RA. Methods. From previously published pharmacokinetic parameters with low-dose MTX therapy, and considering a 50 cm² diffusional area, the target steady state in vitroTD flux for MTX was calculated to be 35 g/cm²/hr. Modified Franz diffusion chambers and hairless mouse skin were used for in vitro skin permeation studies. Hairless mice were used for in vivo studies. Delivered amounts of MTX and EDAM were determined by assaying the receiver phase fluid (or blood) with validated reversed phase HPLC methods. Results. Intrinsic partition coefficient of MTX was low (log P = –1.2). Target MTX fluxes of 35 g/cm²/hr were achievable only with 1–15% (v/v) Azone^® in propylene glycol (PG). Flux of EDAM (85 g/cm²/hr) was higher than MTX from an isopropyl alcohol (IPA)—5% (v/v) Azone^® system. Clinically significant steady state in vivo blood concentration of MTX and EDAM was achieved using delivery systems containing 2.5% Azone^® in PG. Area under the drug concentration-time curves (AUC_0–24hr) for MTX were 2379 and 3534 ng*hr/ml from PG—2.5% Azone^® and PG—7.5% Azone^® systems respectively. AUC_0-24hr of EDAM was 6893 ng*hr/ml using a PG—2.5% Azone^® system. Conclusions. Results of this study show the feasibility of using a transdermal delivery system of MTX and EDAM for the treatment of rheumatoid arthritis.     

Microdialysis Technique as a Method to Study the Percutaneous Penetration of Methyl Nicotinate Through Excised Human Skin,Reconstructed Epidermis,and Human Skin In Vivo

Purpose. The aim was to assess the feasibility of cutaneousmicrodialysis as a method to study percutaneous penetration of methyl nicotinatethrough human skin in vitro and in vivo. Methods. Microdialysis was applied in vitro in excised human skin,in isolated dermis, in reconstructed human epidermis and in vivo inthe volar forearm skin of volunteers using methyl nicotinate (MN) asa model compound. After topical application of MN, aliquots of theperfusate were collected and analyzed for the presence of MNspectrophotometrically and by HPLC. In vivo, visual scoring and laser Dopplerperfusion imaging (LDPI) were used to monitor the effects on skinblood flow. Results. In vitro, MN was detected in the dialysate after a 1 minexposure of excised skin to concentrations as low as 25 mM. Higherconcentrations up to 500 mM showed increased levels. Prolongationof the application time to 60 min resulted in increased levels of MNin the perfusate as the duration of application increased. Reconstructedepidermis and isolated dermis showed an almost 2- and 20-fold higherpenetration compared to excised skin, respectively. In vivo, LDPImeasurements showed a rapid increase in skin blood flow afterapplication of 25 to 100 mM MN for 1 min. MN was only detectable inthe microdialysate after application of 100 mM for 10 min (two ofthree subjects). Conclusions. Cutaneous microdialysis may be a tool for comparativestudies linking responses in human skin in vivo to in vitro data usingthe same technique and endpoint.     

Iontophoresis Enhances the Transport of Acyclovir Through Nude Mouse Skin by Electrorepulsion and Electroosmosis

Purpose. Iontophoresis was employed for enhancing the transdermal delivery of acyclovir through nude mouse skin in vitro, with the aim of understanding the mechanisms responsible for drug transport, in order to properly set the conditions of therapeutical application. Methods. Experiments were done in horizontal diffusion cells, using as donor a saturated solution of acyclovir at two different pH values (3.0 and 7.4). Different electrical conditions (current density and polarity) were employed. Results. At pH 3.0, acyclovir anodal transport was due to electrorepulsion, since acyclovir was 20% in the protonated form. In acyclovir anodal iontophoresis at pH 7.4 the main mechanism involved was electroosmosis, since the drug was substantially unionized and the negative charge of the skin at this pH caused the electroosmotic flow to be from anode to cathode. In the case of cathodal iontophoresis at pH 3.0, acyclovir transport was enhanced approx. seven times, due to the presence of an electroosmotic contribution caused by the reversal of the charge of the skin. At pH 7.4 during cathodal iontophoresis acyclovir transport was not enhanced because the electroosmotic flow was in the opposite direction, compared to drug electric transport, i.e. anode to cathode. The increased skin permeability caused by current application was demonstrated to be less important than electrorepulsion and electroosmosis. Conclusions. Anodal iontophoresis shows potential applicability for enhancing acyclovir transport to the skin, considering that both electric transport and electroosmosis can be used by appropriately setting the pH of the donor.     

The Influence of Liquid Crystalline Phases on Drug Percutaneous Absorption. II. Permeation Studies Through Excised Human Skin

The influence of liquid crystalline (LC) phases on the percutaneous absorption of a model compound (ploxicromil; PXC) was studied with the use of the phase diagram for the surfactant, oil, and water comprising the vehicles. Two separate sets of vehicles, representing two different tie lines lying in the Ll + LC phase region, were prepared in which the concentration of LC was varied over the range 0 to 100% along each tie line. In vitro permeation studies of PXC from these systems were conducted using excised human skin and the flux values determined as a function of the percentage LC present in the vehicles. In virtually all cases, the flux reached a peak at 5-10% LC and then decreased significantly as the fraction of LC present increased further. The pattern of behavior observed is discussed in terms of current theories describing membrane-controlled and vehicle-controlled diffusion, none of which adequately model the results obtained.     

Azone对安定的体外透皮促进作用

本文研究了含乙醇及丙二醇的水溶液系统中的Azone 对安定的体外透皮促进作用。发现不同浓度的Azone 溶液均可促进安定的透皮吸收,但以其0.8%的溶液作用最强,且有统计学意义。     

Vehicle Effects on in Vitro Percutaneous Absorption Through Rat and Human Skin

We studied the effects of three vehicles (propylene glycol, octanol and ethyl decanoate) with differing polarity on the in vitro percutaneous absorption of three chemicals (fluazifop-butyl, dimethyl phthalate and fomesafen sodium salt) with a range of physico-chemical properties. Absorption rate measurements were made from high vehicle volume (200 µl/cm²) and low vehicle volume (<10 µLl/cm²) applications. For the lipophilic fluazifop-butyl absorption rate was highest from the more polar vehicle propylene glycol, but this effect was only significant under high-volume conditions. There was a variable vehicle effect on absorption of the intermediate chemical dimethyl phthalate. The largest vehicle effect was seen for the more hydrophilic fomesafen sodium salt where absorption was fastest from the least polar vehicle ethyl decanoate. These results support the hypothesis that the absorption process can in part be predicted from a knowledge of solute solubility. Vehicle effects were greater from high volume applications than from those more comparable to occupational exposure conditions.     

Percutaneous Penetration Kinetics of Nitroglycerin and Its Dinitrate Metabolites Across Hairless Mouse Skin in Vitro

The percutaneous penetration kinetics of the antianginal, nitroglycerin (GTN), and its primary metabolites, 1,2- and 1,3-glyceryl dinitrate (1,2- and 1,3-GDN), were evaluated in vitro, using full-thickness hairless mouse skin. GTN and the 1,2- and 1,3-GDNs were applied (a) in aqueous solution as pH 7.4 phosphate-buffered saline (PBS) and (b) incorporated into lipophilic ointment formulations. The cutaneous transformation of GTN to its dinitrate metabolites was detected, but no interconversion between 1,2-GDN and 1,3-GDN was observed. Following application of the nitrates in PBS solution, all three compounds exhibited steady-state transport kinetics. The steady-state flux of GTN (8.9 ± 1.5 nmol cm^–2 hr^–1) was significantly greater (P < 0.05) than those of 1,2-GDN (0.81 ± 0.54 nmol cm^–2 hr^–1) and 1,3-GDN (0.72 ± 0.20 nmol cm^–2 hr^–1). The corresponding permeability coefficient () for GTN (20 ± 3 × 10^–3 cm hr^–1) was significantly larger than the corresponding values for 1,2-GDN (1.4 ± 0.9 × 10^–3 cm hr^–1) and 1,3-GDN (1.2 ± 0.4 × 10^–3 cm hr^–1), which were statistically indistinguishable (P > 0.05). Further analysis of the transport data showed that the differences between GTN and the GDNs could be explained by the relative stratum corneum/water partition coefficient (K _s) values of the compounds. The apparent partition parameters, defined as = K _s · h [where h is the diffusion path length through stratum corneum (SC)] were 19.8 ± 2.5 × 10^–2 cm for GTN and 1.91 ± 1.07 × 10^–2 and 1.81 ± 0.91 × 10^–2 cm for 1,2- and 1,3-GDN, respectively. However, when the nitrates were administered in an ointment base, the apparent partition parameter (') and permeability coefficient (') of GTN markedly decreased, to 2.51 ± 0.75 × 10^–2 cm and 1.6 ± 0.3 × 10^–3 cm hr^–1, respectively. In contrast, the ' and ' results for 1,2- and 1,3-GDN were not significantly different (P > 0.05) from the corresponding and values, which were measured following dosing as aqueous solutions. As a result, the steady-state fluxes of all three nitrates from the ointment formulation were comparable (GTN, 154 ± 28 nmol cm^–2 hr^–1; 1,2-GDN, 162 ± 22 nmol cm^–2 hr^–1; 1,3-GDN, 162 ± 34 nmol cm^–2 hr^–1). It follows that the dinitrates can be as efficiently delivered across the skin as GTN when a suitable formulation is employed. This finding may support transdermal therapy using 1,2- or 1,3-GDN if, indeed, they are found to be pharmacologically effective.     

Structure/Effect Studies of Fatty Acid Isomers as Skin Penetration Enhancers and Skin Irritants

Comparisons were made of branched vs unbranched saturated fatty acids and cis vs trans unsaturated fatty acids as skin penetration enhancers and primary skin irritants. Skin penetration studies used naloxone base as the diffusant, propylene glycol as the vehicle, and human skin. Maximum naloxone flux was with C_9–12-branched and unbranched fatty acids. For C_5–14 fatty acids, branched and unbranched isomers had similar effects. One branched C₁₈ fatty acid isomer (C₁₆-branched isostearic acid) was more effective in enhancing skin penetration than a differently branched (C₂-branched isostearic acid) or unbranched C₁₈ isomer (stearic acid). There was no significant difference between cis and trans unsaturated C_16–18 fatty acid isomers in their effects on naloxone flux, and all unsaturated fatty acids were more effective enhancers than the corresponding saturated isomers. Several of these fatty acid/propylene glycol vehicles were evaluated in a rabbit primary skin irritation test. Irritation indices were poorly correlated with the effectiveness of the vehicles in enhancing naloxone flux. It was possible to enhance naloxone skin penetration greatly with a vehicle with only minimal skin irritation potential.     

透皮促进剂对萘普生的促透效果研究

目的研究透皮促进剂月桂氮酮、油酸、月桂醇与1,2-丙二醇单独使用或混合使用对萘普生经皮渗透的促透效果。方法采用Valia-Chien双室渗透池,以10%聚乙二醇400生理盐水为接收介质,经大鼠腹部离体皮肤渗透,高效液相色谱法测定接受液中药物含量,计算药物累积透皮量和稳态透皮速率。结果 5%月桂氮酮+20%1,2-丙二醇达最大促透效果。结论脂溶性促进剂月桂氮酮、油酸,联合1,2-丙二醇使用对萘普生促透效果显著。     

基质pH及促渗剂对阿昔洛韦水凝胶贴剂体外透皮性能的影响

分别制备了基质pH为5.0、6.0、7.5的不含促渗剂的阿昔洛韦水凝胶贴剂,在基质pH 6.0的处方中加入不同浓度的月桂氮革酮、Ⅳ.甲基吡咯烷酮(NMP)、薄荷醇、吐温-80、聚乙二醇(PEG)400作为促渗荆,以考察基质pH及促渗剂对阿昔洛韦透过离体小鼠皮肤的影响.结果表明,基质pH升高,阿昔洛韦的透皮速率增大.与不含促渗剂的基质pH6.0处方组对照,NMP、PEG 400单用不能提高阿昔洛韦的渗透速率,4%的吐温-80、薄荷醇和月桂氮革酮均可提高阿昔洛韦的经皮渗透.     

双氯芬酸钠柔性脂质体的制备及其对离体小鼠皮肤的透皮效果

利用同离子效应制备双氯芬酸钠柔性脂质体,并考察脂质浓度对包封率的影响.同时比较了双氯芬酸钠乳膏、传统脂质体与柔性脂质体对离体小鼠皮肤的透皮效果.结果表明,同离子效应可显著增大柔性脂质体的包封率,较理想的脂质浓度为卵磷脂-胆酸钠为6∶1.2(g,w/w),离体小鼠皮肤12h累积透过率依次为:柔性脂质体＞＞传统脂质体＞乳膏.     

The Enhancer Effect of Several Phenyl Alcohols on Percutaneous Penetration of 5-Fluorouracil

Pharmaceutical Research -     

Matrix-Type Transdermal Patches of Verapamil Hydrochloride: In Vitro Permeation Studies Through Excised Rat Skin and Pharmacodynamic Evaluation in Rats

The objectives of this study were to develop matrix-type transdermal patches of verapamil hydrochloride (VRP) with pectin as a matrix polymer to investigate the influence of several terpenes on in vitro permeation of VRP through rat skin and to evaluate pharmacodynamic activity of transdermal formulations in rats. Matrix-type transdermal patches containing VRP were prepared using pectin as a matrix agent and propylene glycol as a plasticizer agent. Terpenes such as nerolidol, d-limonene, eucalpytol, menthone, and menthol were also used as a chemical enhancer to improve the skin penetration of VRP. The permeation studies were perfomed using Franz-type diffusion cells and full-thickness excised abdominal rat skin. Effects of terpenes on the permeation parameters of VRP were evaluated. In vitro skin permeation studies showed that nerolidol was the most promising enhancer among the enhancers examined in the present study, followed by d-limonene. Pharmacodynamic activity of the transdermal patches containing nerolidol or d-limonene was evaluated in rats by the measurement of systolic blood pressure for 360 min with the use of the tail cuff method. VRP transdermal patches significantly decreased the systolic blood pressure after 30 min and transdermal patches containing nerolidol and d-limonene maintained the decrease in blood pressure during the observation of 360 min.     

渗透促进剂对止泻凝胶膏中胡椒碱透皮的影响

制备含不同渗透促进剂的止泻凝胶膏,采用Franz扩散池考察各处方的体外透皮行为.采用HPLC法测定制品中胡椒碱含量.结果表明,当促渗剂以4％的浓度单用时,N-甲基吡咯烷酮(NMP)的促渗效果最好,月桂氮时酮和1,2-丙二醇的效果相近.促进剂组合使用时促进胡椒碱透皮的作用更强,其中4％月桂氮艰酮+4％丙二醇+8％ NMP为本复方的渗透促进剂时效果较好.     

Mechanism of In Vitro Percutaneous Absorption Enhancement of Carvedilol by Penetration Enhancers

The effect of penetration enhancers like tulsi (basil) oil, eucalyptus oil, clove oil, black cumin oil, oleic acid and Tween 80 on the percutaneous absorption of model lipophilic drug-carvedilol was investigated using excised rat abdominal skin. Transdermal flux, permeability coefficient and enhancement factor were calculated for each penetration enhancer. Black cumin oil (5% v/v) was selected on the basis of its highest enhancement in permeation and was evaluated further for its mode of action using DSC, FTIR and histological studies. The results indicated that the oil shows its action by extraction of lipids from stratum corneum as well as by loosening the hydrogen bonds between ceramides subsequently leading to fluidization of the lipid bilayer.     

Physicochemical Aspects of Percutaneous Penetration and Its Enhancement

The classic diffusion model-based interpretation of percutaneous absorption is compared to a simple kinetic analysis. The physicochemical significance and the major deductions of the two approaches are shown to be in general agreement. In particular, the effect of penetrant oil/water partition coefficient on transdermal flux is consistently predicted by the two models. Diffusional and kinetic assessments of skin penetration enhancement are then shown to reveal similar dependencies upon penetrant physical chemistry. It is demonstrated that the requirements for successful promotion of a lipophilic drug's transdermal flux are quite different from those necessary for a hydrophilic penetrant. Finally, in light of published transport data and our increased comprehension of the stratum corneum barrier function, the evidence for (and significance of) different absorption paths across the stratum corneum is considered. In addition, the impact of penetrant size on transport is addressed. It is argued that currently held beliefs concerning (i) a putative polar route through the stratum corneum and (ii) the dependence of flux on molecular weight warrant considerable further attention before their unequivocal acceptance is appropriate.     

Skin Penetration and Metabolism of Topical Glucocorticoids in Reconstructed Epidermis and in Excised Human Skin

Purpose. To investigate pharmacokinetic differences between the non-halogenated double ester prednicarbate (PC) and the fluorinated monoester betamethasone 17-valerate (BM17V) their metabolism in human keratinocytes and fibroblasts as well as their permeation and biotransformation in reconstructed epidermis and excised human skin was compared. Special attention was given to the 17-monoesters because of their high receptor affinity and antiproliferative effects. Methods. Glucocorticoid penetration was determined using Franz diffusion cells, quantifying metabolite concentrations by HPLC. Chemical stability and reactivity of the monoesters was determined by molecular modeling analysis. Results. PC accumulated in the stratum corneum. A considerable amount of penetrating PC was hydrolyzed by viable keratinocytes to prednisolone 17-ethylcarbonate (P17EC). P17EC permeated the skin very rapidly when compared to BM17V. Overall P17EC concentrations in viable tissue were low. Inside of the acceptor fluid, but not within the tissue, P17EC was converted to the more stable prednisolone 21-ethylcarbonate (P21EC). Conclusions. The inactivation of highly potent, but also cell toxic, 17-monoesters to almost inactive 21-congeners seen with isolated cell monolayers appears less important in the skin. In vitro determination of the dermal 17-monoesters concentrations may allow the prediction of the atrophogenic risk in man. BM17V levels exceeding P17EC concentrations about 6-fold may contribute to its lower tolerance when compared to PC.