Effect of Dosing Vehicle on the Dermal Absorption of Fluazifop-butyl and Fomesafen in Rats in Vivo

One important factor which may influence the extent and rateof percutaneous absorption is the dosing vehicle. The purposeof the experiments described was to compare the effect of dosingvehicles of different polarities on the absorption of two herbicidesacross rat skin in vivo. Rats were dosed dermally with eitherfluazifop-butyl (logP_oct 4.5) or fomesafen sodium salt (log-P_oct-1.2) in propylene glycol (PG), octanol (OCT), or ethyl decanoate(ED), and the amount of radioactivity excreted in urine wasdetermined. Absorption rates were estimated from the urinaryexcretion data and from blood kinetic data derived from intravenouslydosed rats. For fluazifop-butyl the average rate of absorption(x10^-2 ug/hr^-1 ±SE) was not greatly influenced by thedosing vehicle (OCT, 2.94 ± 0.08; ED, 3.66 ± 0.10;PG, 3.95 ± 0.32) despite relatively large differencesin solubility (PG, 38 mg/ml; OCT, and ED, >600 mg/ml). Theseresults were consistent with the finding that there was at mostonly a twofold difference in the epidermal membrane:vehiclepartition coefficients (km). In contrast, the absorption rateof fomesafen from PG (1.98 ± 0.04) was approximatelyhalf that of ED (3.98 ± 0.06) and OCT (4.49 ±0.08) for the first 30 hr after application and was in keepingwith solubility data (PG, 638 mg/ml; OCT, 12 mg/ml; ED, <10 mg/ml). At later time points the absorption of fomesafenfrom PG increased; this is discussed in relation to the penetration-enhancingproperties of PG. The dermal absorption potential for fomesafenis dependent on the solubility of the polar compound in thevehicle while for the more lipophillic fluazifop-butyl, measurementof vehicle/skin partition coefficients may be a more appropriatepredictor of absorption.     

In Vivo Percutaneous Absorption of Hydrocortisone: Multiple-Application Dosing in Man

Percutaneous absorption of hydrocortisone was measured in six healthy adult men from whom informed consent had been obtained. The study compared a single topical dose to multiple-topical dose treatments (one vs three applications) on the same day. ¹⁴C-Labeled hydrocortisone in acetone was applied to 2.5 cm² of ventral forearm skin and protected with a nonocclusive polypropylene chamber. The amount of ¹⁴C measured in urine collected over 7 days was used to determine hydrocortisone absorption. The treatments, performed 2 to 3 weeks apart, each utilized adjacent sites on the same individuals. A single dose of 13.33 µg/cm² delivered 0.056 µg/cm² of hydro-cortisone through the skin. When the single dose was tripled to 40 µg/cm², the amount delivered through the skin increased by nearly three times, from 0.056 to 0.140 µg/cm²; the expected delivery was 3 x 0.056 µg/cm² = 0.168 µg/cm². Three serial doses of 13.33 µg/ cm² (total, 40 µg/cm²) were also expected to deliver 0.168 µg/cm² with or without soap and water washing between doses, but the observed amount of hydrocortisone delivered through the skin significantly exceeded our expectations. This indicates that multiple-dosing treatments resulted in a significant increase in bioavailability. It is postulated that increased vehicle application and washing dissolved and mobilized previously dosed hydrocortisone and increased bioavailability.     

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.     

In vitro permeation of diclofenac sodium from novel microemulsion formulations through rabbit skin

In order to increase topical penetration of the nonsteroidal anti‐inflammatory drug, diclofenac sodium, new microemulsion formulations were prepared to increase drug solubility and in vitro penetration of the drug. The influence of dimethyl sulfoxide and propylene glycol were also investigated as enhancers on the in vitro penetration of diclofenac sodium using Franz diffusion cells using excised dorsal rabbit skin. Factorial randomized design was performed to analyze the results of in vitro permeation studies. Microemulsions prepared with isopropyl alcohol were superior to those prepared with propanol. Enhancers had different effects depending on the formulation. Propylene glycol was superior to dimethyl sulfoxide when incorporated into isopropyl alcohol microemulsion, whereas dimethyl sulfoxide was superior to propylene glycol in propanol microemulsions. There were no observable histopathological differences between the skin of the control group and the treated groups at the light microscope level due to swelling of the skin tissue. The present study shows that microemulsion formulations containing isopropyl alcohol as co‐surfactant and propylene glycol as enhancer represent a promising approach for a topical vehicle for diclofenac sodium. Drug Dev. Res. 65:17–25, 2005. © 2005 Wiley‐Liss, Inc.     

Improved acitretin delivery through hairless mouse skin by cyclodextrin complexation

The effects of four cyclodextrins, i.e., 2-hydroxypropyl-β-cyclodextrin, randomly methylated β-cyclodextrin (MβCD), γ-cyclodextrin and 2-hydroxypropyl-γ-cyclodextrin, on the aqueous solubility of acitretin were investigated. Of the four cyclodextrins tested MβCD displayed the largest effect. The aqueous solubility of the drug could be increased even further by pH adjustment. Thus, the solubility of acitretin in an aqueous pH 7.5 buffer solution containing 23% (w/v) MβCD was determined to be 1.96 mg/ml. Acitretin is insoluble in water. The flux of acitretin through hairless mouse skin was determined to be 0.032 mg h⁻¹ cm⁻² from a pure propylene glycol vehicle but 0.201 mg h⁻¹ cm⁻² from an aqueous MβCD containing vehicle.     

Noninvasive in Vivo Percutaneous Absorption Measurements Using X-Ray Fluorescence

X-ray fluorescence (XRF) has been used to determine in vivo the percutaneous absorption of 5-iodouracil (5IU) in dimethyl sulfoxide (DMSO) on female Sprague-Dawley rats. An average absorption rate constant of 122 ± 34 µg/cm²-hr was obtained from the XRF measurements on four rats. A comparative study was performed with radiolabeled (¹²⁵I) 5IU in which the absorption rate constant was determined to be 126 ± 20 µg/cm²-hr. The XRF system described provides a simple, noninvasive means of measuring the percutaneous absorption rate of select compounds by the surface disappearance method.     

Percutaneous Penetration Enhancement in Vivo Measured by Attenuated Total Reflectance Infrared Spectroscopy

A novel application of attenuated total reflectance IR Spectroscopy (ATR-IR) was used to monitor the outer several microns of the stratum corneum (SC) and, thereby, demonstrate enhanced percutaneous absorption in vivo in man. 4-Cyanophenol (CP) as a model permeant yielded a unique IR signal, distinct from those of the stratum corneum and the vehicle components. CP was administered for 1, 2, or 3 hr as a 10% (w/v) solution either in propylene glycol or in propylene glycol containing 5% (v/v) oleic acid. The absorbance at 2230 cm^–1, which corresponded to CN bond stretching, diminished significantly faster when CP was codelivered with oleic acid. An IR absorbance due primarily to propylene glycol at 1040 cm^–1 (C–O stretching) also disappeared more quickly following application of the enhancer-containing solution. In addition, only the formulations with oleic acid induced a higher wavenumber shift in the frequency of the asymmetric C–H bond stretching absorbance. This change indicates increased lipid-chain disorder, the mechanism by which oleic acid is believed to cause enhanced drug transport across the stratum corneum. Therefore, ATR-IR permits one to examine noninvasively the kinetics, extent, and mechanism of percutaneous penetration enhancement in vivo in human subjects.     

Influence of vehicles on the in vitro percutaneous absorption of piroxicam to optimise the formulation of patch tests in dermatology

The present study evaluated the influence of various vehicles on the in vitro percutaneous absorption of piroxicam across human skin under standard diffusion conditions to optimise the formulation of patch tests in dermatology. The transdermal permeation properties of piroxicam were evaluated from five vehicles (PEG 400, propylene glycol, transcutol P, petrolatum, and petrolatum + transcutol P 10%) using Franz diffusion cells. Piroxicam was applied as a saturated solution in vehicles to ensure equal thermodynamic activity of piroxicam in the vehicles. Concentrations of piroxicam were determined by high performance liquid chromatography in epidermis, dermis, and receptor liquid. The release of piroxicam from its vehicles and consequently its cutaneous absorption are influenced by the vehicle assayed and the solubility of piroxicam in each vehicle. The penetration of piroxicam through human skin was clearly enhanced by propylene glycol and petrolatum + transcutol P 10%, with cumulated amounts of piroxicam in the receptor fluid at 48 h of 116±32 and 159±28 μg/mg/cm² respectively, whereas petrolatum alone did not allow the diffusion of piroxicam. Additional experiments should be conducted in vivo to correlate the results obtained in vitro and to provide clinicians with a more reliable diagnostic test. Drug Dev. Res. 58:283–290, 2003. © 2003 Wiley‐Liss, Inc.     

Experimental factors affecting in vitro absorption of six model compounds across porcine skin

This comparative study evaluated the effect of several experimental variables on the absorption of six model [¹⁴C]-labeled compounds (caffeine, cortisone, diclofenac sodium, mannitol, salicylic acid, and testosterone) through porcine skin. Using static and flow-through diffusion cells, finite or infinite, saturated or unsaturated doses were applied in one of three vehicles: propylene glycol, water, and ethanol following a full factorial experimental design. The flux of each compound into the receptor phase, with or without bovine serum albumin (BSA), was monitored over 24 h. Levels of radioactivity were also determined in the stratum corneum by tape stripping and in the remaining skin. Apparent permeability coefficients (Kp) and dose absorbed were calculated and compared. The overall results emphasize the importance of experimental design and confirm previous findings that identified dose volume, saturation level and vehicle as the main sources of variation in the in vitro assessment of dermal absorption, whilst diffusion cell model and the presence/absence of BSA in the receptor phase had minimal effect. Although the acquired data do not directly reveal new mechanistic information on dermal absorption, the unique and complete study design has provided a suitable data source for the development of dermal absorption prediction models.     

The Effect of Ultrasound on the in Vitro Penetration of Ibuprofen Through Human Epidermis

The objective of this study was to develop an in vitro method to investigate the effect of ultrasound on the in vitro absorption of ibuprofen from a propylene glycol/water vehicle through human epidermis. A diffusion cell was modified so ultrasound could be applied to the vehicle and skin. Since ultrasound can increase the temperature underneath the area of application, control representing temperature effects ran concurrently to the ultrasound experiment. The results demonstrate that ultrasound can increase the penetration of ibuprofen through human skin. This increase in diffusion was greater than for controls where an equivalent increase in temperature was utilized. The results also indicate that evaporation of vehicle components may alter the skin/vehicle partition coefficient, decreasing the effects of ultrasound on the penetration of ibuprofen through the skin.     

Studies of in vitro skin permeation and retention of a leukotriene antagonist from topical vehicles with a hairless guinea pig model.

A leukotriene antagonist [Ro 23-3544; 6-acetyl-7-[5-(4-acetyl-3-hydroxy-2-propylphenoxy)pentyloxy] -3,4-dihydro-2H-1-benzopyran-2-carboxylic acid; 1] was studied in vitro for its permeation through and retention in hairless guinea pig skin from various topical vehicles. Both the free acid and the sodium salt forms of the drug were used. The vehicles evaluated were polyethylene glycol 400, propylene glycol, dimethyl sulfoxide (DMSO), C12-C15 alcohol lactates, dimethyl isosorbide, butyrolactone, methylpyrrolidone, hexyl laurate, isopropyl myristate, and caprylic/capric triglyceride (Neobee M5). For the salt form of the drug, the highest permeability coefficient and retention were obtained from DMSO and methylpyrrolidone, respectively. For the acid form, however, the highest permeability coefficient and retention were obtained from hexyl laurate and DMSO, respectively. The highest permeation and retention values were not obtained from the same vehicle for either the salt or the acid form of the drug. This observation questions the validity of using permeation (flux) measurements to screen topical drugs and formulations. Although the precise reasons for this lack of correlation between permeation and retention are not known at this time, this study has shown that the solubility parameters of the drug and the vehicles used may play an important role. It seems logical to conduct skin retention studies rather than flux measurements in evaluating drug delivery from dermatological products.     

乙醇和丙二醇单用与联用对曲安奈德喷雾溶液透皮性能的影响

目的 对曲安奈德喷雾溶液进行体外透皮试验,考察乙醇和丙二醇单用与联用时对曲安奈德喷雾溶液体外透皮功能的影响。方法 选取新西兰白兔腹部皮肤,用Franz扩散池法对曲安奈德喷雾溶液进行体外透皮试验,用高效液相色谱法（HPLC）测定曲安奈德含量,用单因素方差分析法对各组间的透皮吸收速率进行对比分析。结果 乙醇和丙二醇联用时的透皮吸收速率均显著高于单用时的透皮吸收速率（P<0.05）,且乙醇和丙二醇联用时对曲安奈德喷雾溶液的促透作用顺序为10%乙醇+25%丙二醇>10%乙醇+20%丙二醇>15%乙醇+25%丙二醇>15%乙醇+20%丙二醇。结论 10%乙醇和25%丙二醇联用时可使曲安奈德喷雾溶液的透皮功能达到最佳化。     

Orally active esters of cephalosporin antibiotics. II. Synthesis and biological properties of the acetoxymethyl ester of cefamandole

The synthesis of the acetoxymethyl (AOM) ester of cefamandole (CM) is described. The sparingly soluble ester is shown to be well absorbed orally by mice, but only when administered in solution in a partially non-aqueous vehicle, 50% propylene glycol. Neither the ester in aqueous suspension nor the sodium salt of CM in solution is well absorbed orally. The rate of oral absorption of the ester from solution is very rapid as shown by the early peak time and shape of the plasma level curve. Oral bioavailability from solution is at least 60% and is apparently limited only by hydrolysis or precipitation of a variable portion of the ester dose in the intestinal lumen prior to absorption.     

Transdermal delivery of nicardipine: an approach to in vitro permeation enhancement

Nicardipine hydrochloride (NC-HCl), a calcium channel blocker for the treatment of chronic stable angina and hypertension, seems to be a potential therapeutic transdermal system candidate, mainly due to its low dose, short half-life, and high first-pass metabolism. The objective of the present study was to evaluate its flux and elucidate mechanistic effects of formulation components on transdermal permeation of the drug through the skin. Solubility of NC-HCl in different solvent systems was determined using a validated HPLC method. The solubility of drug in various solvent systems was found to be in decreasing order as propylene glycol (PG)/oleic acid (OA)/dimethyl isosorbide (DMI) (80:10:10 v/v) > PG > PG/OA (90:10 v/v) > polyethylene glycol 300 > ethanol/PG (70:30 w/w) > transcutol > dimethyl isosorbide (DMI) > ethanol > water and buffer 4.7 > 2-propanol. Propylene glycol was then selected as the main vehicle in the development of a transdermal product. As a preliminary step to develop a transdermal delivery system, vehicle effect on the percutaneous absorption of NC-HCl was determined using the excised skin of a hairless guinea pig. Vehicles investigated included pure solvents alone and their selected blends, chosen based on the solubility results. In vitro permeation data were collected at 37 degrees C, using Franz diffusion cells. The skin permeation was then evaluated by measuring the steady state permeation rate (flux) of NC-HCl, lag time, and the permeability constant. The results showed that no individual solvent was capable of promoting NC-HCl penetration. Permeation profiles of the drug through hairless guinea pig skin using saturated solutions of drug were constructed. Among the systems studied, the ternary mixture of PG/OA/DMI and binary mixture of PG/OA showed excellent flux. The flux value of the ternary system was nearly three times higher than the corresponding values obtained for the binary solvent. A similar trend also was observed for the permeation constant, while the values of lag time were reversed. The ternary mixture was then selected as a potential absorption enhancement vehicle for the transdermal delivery of drug. In general, higher fluxes were observed through hairless guinea pig skin as compared with the human stratum corneum. Based on the results obtained from the release study of NC-HCl from saturated solutions of the drug, a novel lecithin organogel (microemulsion-based gel) composed of soybean lecithin, propylene glycol, oleic acid, dimethyl isosorbide, and isopropyl myristate was developed as a possible matrix for transdermal delivery of NC-HCl. In vitro percutaneous penetration studies from this newly developed gel system through giunea pig skin and human stratum corneum revealed that the organogel system has skin-enhancing potential and could be a promising matrix for the transdermal delivery of nicardipine. Furthermore, higher permeation rates were observed when nicardipine free base was incorporated into the gel matrix instead of hydrochloride salt.     

Absorption of Sunscreens and Other Compounds Through Human Skin in Vivo: Derivation of a Method to Predict Maximum Fluxes

Purpose. The goal of this study was to quantify the transdermally absorbed amounts of the sunscreens octyl dimethyl p-aminobenzoic acid, oxybenzone, 4-isopropyl-dibenzoylmethane, 3-(4-methylben-zylidene)-camphor, isoamyl-4-methoxycinnamate, the repellent and plasticizer dibutyl phthalate, the antioxidant 3.5-di-t-butyl-4-hydroxyanisol, and the antimicrobial compounds butyl-4-hydroxybenzoate, biphenyl-2-ol, and 2,4,4-tri-chlor-2-hydroxydiphenylether (tri-closane). Permeabilities P _B and maximum fluxes J _max should be correlated with relevant physicochemical properties. Methods. Saturated solutions of the above-mentioned compounds in a propylene glycol/water mixture were applied to the skin using glass chambers which were fixed to the upper arms of volunteers. Maximum fluxes were calculated from concentration decreases in the vehicle. Results. A linear relationship between the logarithms of permeabilities P _B of the penetrants (0.02–0.28 cm h^–l) and the corresponding octanol/vehicle partition coefficients PC _Oct/v (166–186,208) was found. Consequently, the influence of aqueous boundary layers could be neglected. However, the slope of the resulting straight line of 0.38 is considerably smaller than unity indicating that PC _Oct/v does not represent the lipophilicity of the stratum corneum adequately. Maximum fluxes range from 0.5 to 130 µg cm^–2 h^–1. A general equation for the calculation of J _max was derived based on experimental data taking into account the PC _Oct/v and the solubilities c _sV of the respective penetrants in the vehicle.     

Rectal absorption enhancement of rate-controlled delivered ampicillin sodium by sodium decanoate in conscious rats

Because of the relatively poor intestinal absorption of ampicillin sodium, efforts have been made to enhance ampicillin absorption by co-administration of absorption promoters. In the present study the enhancing effect of sodium decanoate on rate and extent of rectal ampicillin absorption in rats has been evaluated after rate-controlled and site-controlled delivery of aqueous solutions. Rectal absorption without enhancer was extremely low (8±7%), and the addition of 0.032M sodium decanoate gave comparable values. However, administration in 0.16M decanoate considerably increased ampicillin bioavailability, to 79±30%, whereas the absorption rate was not significantly affected.     

The feasibility study of transdermal drug delivery systems for antidepressants possessing hydrophilicity or hydrophobicity

The feasibility studies on the transdermal drug delivery systems have been performed to avoid the systemic side-effects and gastric disorders that could be occurred due to the transient high blood concentration after oral administration of antidepressants such as venlafaxine HCl and citalopram. When surfactants of tween 80^? and plasticizer of diethyl phthalate were combined with citalopram?Cethylene vinyl acetate (EVA) matrix, the permeation of citalopram showed the best enhancement. As well as, venlafaxine HCl gels were prepared using carbomer, oleic acid and/or propylene glycol to enhance the skin permeation of venlafaxine HCl. The citalopram-EVA matrix containing tween 80^? and diethyl phthalate as permeation enhancers might be a good transdermal delivery system for providing sustained plasma concentrations of citalopram. Also, venlafaxine HCl showed the possibility to be enhanced skin permeation in the formulation of gels with carbomer including penetration enhancer, oleic acid and/or propylene glycol.     

Effect of vehicles and sodium lauryl sulphate on xenobiotic permeability and stratum corneum partitioning in porcine skin

Dermal contact with potentially toxic agricultural and industrial chemicals is a common hazard encountered in occupational, accidental spill and environmental contamination scenarios. Different solvents and chemical mixtures may influence dermal absorption. The effects of sodium lauryl sulphate (SLS) on the stratum corneum partitioning and permeability in porcine skin of 10 agricultural and industrial chemicals in water, ethanol and propylene glycol were investigated. The chemicals were phenol, p-nitrophenol, pentachlorophenol, methyl parathion, ethyl parathion, chlorpyrifos, fenthion, simazine, atrazine and propazine. SLS decreased partitioning into stratum corneum from water for lipophilic compounds, decreased partitioning from propylene glycol and did not alter partitioning from ethanol. SLS effects on permeability were less consistent, but generally decreased permeability from water, increased permeability from ethanol and had an inconsistent effect on permeability from propylene glycol. It was concluded that, for the compounds tested, partitioning into the stratum corneum was determined by the relative solubility of the solute in the donor solvent and the stratum corneum lipids. Permeability, however, reflected the result of successive, complex processes and was not predictable from stratum corneum partitioning alone. Addition of SLS to solvents altered partitioning and absorption characteristics across a range of compounds, which indicates that partition coefficients or skin permeability from neat chemical exposure should be used with caution in risk assessment procedures for chemical mixtures.     

Drug and vehicle deposition from topical applications: use of in vitro mass balance technique with minoxidil solutions.

The disposition of minoxidil and propylene glycol from topical solutions was measured by using an in vitro mass balance technique. The experimental approach included assessment of the following compartments of the skin and the diffusion cell as a function of time: (1) donor compartment; (2) hairless mouse skin surface, epidermis, and dermis; and (3) receiver compartment. Excellent mass balance was achieved for minoxidil at three doses. However, the recovery of propylene glycol depended on both application volume and time. The experiment involving the evaporation of propylene glycol and water from the propylene glycol:ethanol:water (20:60:20, v/v) mixture, which was placed in the well of a tissue culture plate at room temperature and 37 degrees C, substantiated the loss of vehicles to the air. When a thin application of 20 microL/cm2 was used, 60% of the propylene glycol was unaccounted for after 16 h. The evaporation of propylene glycol concentrated the solution to supersaturation, precipitated out the drug, and then stabilized the thermodynamic activity of the drug in the vehicle. The amount of formulation applied influences the rate of concentration and, thus, the time at which minoxidil precipitates. The precipitation limits the amount of minoxidil that can be absorbed and leads to poor percutaneous absorption of drug from the formulation.     

Effect of neat and binary vehicle systems on the solubility and cutaneous delivery of piperine

Vitiligo is a skin disease characterized by depigmentation disorders due to lack of melanin production. Piperine, an alkaloid extracted from black piper, is active in melanocytes proliferation. To achieve this, the drug has to reach the melanocytes which exist in the deep layer of the epidermis. Higher drug concentration can be obtained after application of optimized formulation to skin. Accordingly, the aim of this work is to investigate the effect of vehicles on skin penetration of piperine as the first step in development of optimized formulation. The tested vehicles include ethanol (Eth), propylene glycol (PG), polyethylene glycol 400 (PEG), and oleic acid (OA) and their combinations. Water was used as the control and skin permeation was monitored using rabbit ear model skin. The highest piperine solubility (48.6?mg/ml) and flux (40.8?μg/cm²?h) was achieved by Eth and the lowest piperine flux (1.17?μg/cm²?h) was reported for PEG. PG and OA showed piperine flux values comparable to that of the control. Among different combination systems, Eth-OA (75:25) binary system had the highest piperine flux (59.3?μg/cm²?h) followed by Eth-OA (50:50) (32.3?μg/cm²?h) and PG-OA (90:10) (22.7?μg/cm²?h). The study thus introduced a vehicle system as the first step in the development of topical formulation of piperine.