Design of Ionic Liquid Formulations with Azone-Mimic Structures for Enhanced Drug Skin Permeation

Although laurocapram (Azone) significantly enhances the skin permeation of drugs, its development was hindered by its skin irritation. We then developed an Azone-mimic ionic liquid (IL-Azone), composed of less irritating cationic ε-caprolactam and anionic myristic acid. IL-Azone dissociates to the original cation and anion in the presence of water in the formulation. We tried to select a formulation suitable for IL-Azone in the present study. Each formulation contained 5 % of either Azone or IL-Azone along with the model drug antipyrine, and skin permeation experiments of the drug were conducted. The results revealed that IL-Azone did not enhance skin permeation when combined with most formulations tested. However, a notable and rapid enhancement in skin permeation was observed when combined with white petrolatum. This effect could be attributed to the minimal water content in white petrolatum, which prevented IL-Azone degradation. Furthermore, its permeation-enhancing effects from IL-Azone in white petrolatum were more pronounced and rapid than Azone. The rapid onset observed with IL-Azone can be attributed to its degradation into its original components at the interface between the stratum corneum and the living epidermis, which results in a shorter lag time before achieving a steady-state concentration in the SC compared to Azone.

A Hollow Microneedle Equipped with a Micropillar for Improved Needle Insertion and Injection of Drug Solution

PURPOSE

Hollow-type microneedles (hMNs) are a promising device for the effective administration of drugs into intradermal sites. Complete insertion of the needle into the skin and administration of the drug solution without leakage must be achieved to obtain bioavailability or a constant effect. In the present study, several types of hMN with or without a rounded blunt tip micropillar, which suppresses skin deformation, around a hollow needle, and the effect on successful needle insertion and administration of a drug solution was investigated. Six different types of hMNs with needle lengths of 1000, 1300, and 1500 µm with or without a micropillar were used.

METHODS

Needle insertion and the disposition of a drug in rat skin were investigated. In addition, the displacement-force profile during application of hMNs was also investigated using a texture analyzer with an artificial membrane to examine needle factors affecting successful insertion and administration of a drug solution by comparing with in vivo results.

RESULTS

According to the results with the drug distribution of iodine, hMN1300 with a micropillar was able to successfully inject drug solution into an intradermal site with a high success rate. In addition, the results of displacement-force profiles with an artificial membrane showed that a micropillar can be effective for depth control of the injected solution as well as the prevention of contact between the hMN pedestal and the deformed membrane.

CONCLUSION

In the present study, hMN1300S showed effective solution delivery into an intradermal site. In particular, a micropillar can be effective for depth control of the injected solution as well as preventing contact between the hMN pedestal and the deformed membrane. The obtained results will help in the design and development of hMNs that ensure successful injection of an administered drug.

Enhanced Physical Stability of L-Ascorbic Acid in an Ionic Liquid

Ionic liquid (IL) technology was used to enhance the stability of L-ascorbic acid (AA). Pyridoxine was selected as the counter cation for anionic AA in IL. After AA was dissolved in water at 40 °C, its ratio decreased to 3.2% after 7 d. In contrast, the IL formulation showed negligible degradation, with almost no loss of AA even after 28 d. These results suggest that the use of IL enhances the stability of AA.

Development of an Auraptene-Loaded Transdermal Formulation Using Non-ionic Sugar Ester Surfactants

Auraptene (Aur) is a naturally occurring monoterpene coumarin ether that exhibits numerous therapeutic properties. Its high lipophilicity and low skin penetration, however, limit its potential application for local and transdermal delivery. Biocompatible non-ionic sugar esters (SEs) possess beneficial properties for the development of transdermal formulations in delivering pharmaceutically challenging molecules such as graphene and Aur. In the present study, we conducted a series of experiments to demonstrate the effect of several previously unstudied SEs on the skin permeation and distribution of Aur by preparing gel- and dispersion-type formulations. Skin permeation and deposition experiments were conducted using a Franz diffusion cell with rat skin as the membrane. The dispersion-type formulations prepared using SEs had higher entrapment efficiency, as well as better skin permeation and retention profiles. The dispersion-type formulation containing sucrose palmitate (sSP) exhibited the highest skin permeation over 8 h. Notably, the enhancement effects on Aur concentration in full-thickness skin after the application of the dispersion-type formulation was higher than those of the control formulation. These results indicated that the prepared formulation has potential for use in the transdermal delivery of Aur in pharmaceutical and cosmetic products.

Viscoelasticity of Liposomal Dispersions

Janus-faced viscoelastic gelling agents-possessing both elastic and viscous characteristics-provide materials with unique features including strengthening ability under stress and a liquid-like character with lower viscosities under relaxed conditions. The mentioned multifunctional character is manifested in several body fluids such as human tears, synovial liquids, skin tissues and mucins, endowing the fluids with a special physical resistance property that can be analyzed by dynamic oscillatory rheology. Therefore, during the development of pharmaceutical or cosmetical formulations-with the intention of mimicking the physiological conditions-rheological studies on viscoelasticity are strongly recommended and the selection of viscoelastic preparations is highlighted. In our study, we aimed to determine the viscoelasticity of various liposomal dispersions. We intended to evaluate the impact of lipid concentration, the presence of cholesterol or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and the gelling agents polyvinyl alcohol (PVA) and hydroxyethylcellulose (HEC) on the viscoelasticity of vesicular systems. Furthermore, the effect of two model drugs (phenyl salicylate and caffeine) on the viscoelastic behavior of liposomal systems was studied. Based on our measurements, the oscillation rheological properties of the liposomal formulations were influenced both by the composition and the lamellarity/size of the lipid vesicles.

Effects of Intradermal Administration Volume Using a Hollow Microneedle on the Pharmacokinetics of Fluorescein Isothiocyanate Dextran (M.W. 4,000)

PURPOSE

Hollow microneedles (hMNs) have been gaining attention as a tool to enable the intradermal (i.d.) administration of pharmaceutical products. However, few reports have examined the effect of administration volume on distribution in the skin and pharmacokinetics parameters after i.d. injection. In the present study, a model middle molecular weight compound, fluorescein isothiocyanate dextran (M.W. 4,000, FD-4), was selected, and blood concentration-time profiles after i.d. and subcutaneous (s.c.) injections with different administration volumes were compared.

METHODS

FD-4 solution was injected i.d. using a hMN or injected s.c. with a 27 G needle. Pharmacokinetics and dermatokinetics of FD-4 were analyzed using a compartment model. The skin distribution of iodine, as an X ray tracer, was used to evaluate drug disposition.

RESULTS

With the administered drug assumed to be absorbed from the broad injection site into blood vessels in the upper and lower dermis by rapid (krapid) and slow (kslow) first-order absorption rate constants, respectively, better agreement of observed and theoretical values was obtained. Furthermore, the fraction, F, of the administered dose absorbed with krapid decreased with the increase in injection volume after i.d. injection, although the pharmacokinetics parameters were almost the same regardless of administration volume after s.c. injection.

CONCLUSION

The drug distribution in the skin may be related to the obtained pharmacokinetics parameters suggested that the number of needles in the MN system and the total administration volume should be considered in designing hMN systems. The present results provide useful information that may support effective drug delivery with hMNs.

Design of an Ante-enhancer with an Azone-Mimic Structure using Ionic Liquid

PURPOSE

Laurocapram (Azone) was broadly examined as a representative enhancer of skin penetration in the 1980s. However, it was not approved for treatment because it caused skin irritation following its penetration into the epidermis through the stratum corneum. In the present study, a so-called ante-enhancer with an Azone-mimic structure was designed based on an ante-drug with negligible systemic toxic effects following its permeation through the skin.

METHODS

The ante-enhancer was designed using ionic liquid technology: an ionic liquid-type ante-enhancer (IL-Azone) with an Azone-mimic structure was prepared from ε-caprolactam and myristic acid as cationic and anionic substances, respectively. The enhancing effects of IL-Azone on the permeation by the following model drugs through pig skin were examined: isosorbide 5-mononitrate (ISMN), antipyrine (ANP), and fluorescein isothiocyanate dextran (FD-4). Skin irritation by IL-Azone was assessed using the Draize method.

RESULTS

The primary irritation index (P.I.I.) of IL-Azone by the Draize method was markedly lower than that of Azone (6.9). Although the ability of IL-Azone to enhance skin penetration was not as high as Azone, IL-Azone moderately increased skin permeation by the model compounds tested (ISMN: 4.7 fold, ANP: 4.5 fold, FD-4: 4.0 fold).

CONCLUSIONS

These results suggest the usefulness of designing a skin penetration enhancer using ionic liquid technology. Further trials on the ionic liquid design with an Azone-mimic structure using other cations and anions may lead to the development of better ante-enhancers.

Remote-controllable dosage management through a wearable iontophoretic patch utilizing a cell phone

With regard to medical treatment through operations, remote control is possible, however, the area of remote-controllable drug treatment is yet to be established. In this study, a prototyped remote-controllable dosage management system that allows patients and caregivers to administer therapeutic drugs via an internet line without touching the dosage device or formulation was developed. This system consists of a transmitter (System A) located away from the patient, and a dosage device (System B) equipped with a receiver (B1), dosage management unit (B2), and a drug treatment unit (B3) that can be installed on the patient. Additionally, Bluetooth® is adopted to communicate from System A to System B. In the present study, System A was incorporated into a cell phone, and System B was a constant-current iontophoresis (IP) device, which was applied on excised pig skin. Sodium salt of betamethasone phosphate (BP^-Na⁺) was selected as a model drug, and the in vitro skin permeation of BP^- was evaluated. As a result, by transmitting the administration information incorporated in System A through B1 to B2, the optimal current was passed between the IP electrodes in B3, and the skin permeation of BP^- was obtained by remote control. That is, the skin permeation of BP^- was obtained by the current flowing from the IP device. The permeation amount decreased when the voltage load was stopped. These results suggested that remote control from System A enables dosing management of bioactive substances from dosage devices applied on the skin, intracutaneously, or subcutaneously without being near the patient. Although various trials are still required to complete the remote-controlled system, the patient does not have to go to the hospital except to take injections. Such drug administrations would lead to decreased medical expenses and increased quality of life for patients.

Prediction of Critical Quality Attributes Based on the Numerical Simulation of Stress and Strain Distributions in Pharmaceutical Tablets

Various stresses and strains are generated on the surface and inside of pharmaceutical tablets when an external force is applied. In addition, stresses in various directions can remain on the surface and inside the tablets because they are generally prepared by compaction of pharmaceutical powders using dies and punches. As it is difficult to measure the stress and strain generation in the tablets experimentally, a numerical simulation was applied by employing a finite element method (FEM). An elastic model is often used to represent stress and strain generation after loading an external force to tablets, and the Drucker-Prager cap (DPC) model has been widely recognized for representing the remaining stress distributions during the compaction of powder to tablet form. Firstly, this article describes an FEM simulation of the stress generation on the surface of the scored tablets after loading the bending force from the back side of the tablets. Next, the FEM simulation was introduced to determine the effect of diametrical compression on the stress and strain generation in the tablets by comparing the results measured experimentally. Furthermore, the residual stresses remaining inside the tablets were simulated using FEM, in which powder compaction was represented as the DPC model. A clear difference was observed in the residual stress distributions between the flat and convex tablets. This indicates that FEM simulation is useful for achieving a science-based understanding of critical quality attributes in various types of tablets.

A Pilot Study of Transdermal Application of Diphenhydramine to the Nasal Ala in Patients with Allergic Rhinitis and Asthma

BACKGROUND

To date, topical allergic rhinitis drugs must be applied intranasally. We studied the efficacy, safety, and impact on co-existing asthma symptoms of transdermal delivery of diphenhydramine through the nasal ala.

METHODS

We enrolled outpatients with symptomatic allergic rhinitis and asthma who were on stable medication for at least 4 weeks. Patients applied diphenhydramine ointment, 0.07 g measured with weighing spoon (0.7 mg diphenhydramine), to the nasal ala twice a day for 2 weeks, followed by 2 weeks' washout. Effects were assessed with the Japanese Allergic Rhinitis Standard Quality of Life Questionnaire (JRQLQ) and Self-assessment of Allergic Rhinitis and Asthma (SACRA) and Asthma Control Test (ACT) questionnaires.

RESULTS

Ten patients participated in the study. Two patients experienced acute exacerbation of asthma during the intervention phase, but no other adverse effects occurred. Self-assessments indicated efficacy in treating nasal symptoms in 5 patients. No significant changes in scores were seen, although mean total JRQLQ score showed a numerical improvement (from 34.3 [21.0] to 14.4 [8.8]; P = 0.0547). Asthma symptoms improved subjectively in 2 patients.

CONCLUSIONS

The efficacy of transdermal application of diphenhydramine on the nasal ala for treating allergic rhinitis was not conclusive, but appears to be effective in certain patients.

Self-Assembled Structure of α-Isostearyl Glyceryl Ether Affects Skin Permeability-a Lamellar with 70-nm Spaces and L3 Phase Enhanced the Transdermal Delivery of a Hydrophilic Model Drug

Self-assembled surfactant structures, such as liquid crystals, have the potential to enhance transdermal drug delivery. In the present study, the pseudo-ternary system of GET (composed of α-Isostearyl glyceryl ether (GEIS) and polysorbate 60)/1,3 butanediol (BG)/water) was shown to exhibit a complex phase diagram. Small- and wide-angle X-ray scattering (SWAXS) and freeze-fracture transmission electron microscopy (FF-TEM) revealed that GET6BG60 (6%GET/60%BG/34%Water) formed a lamellar phase with a repeated distance of approximately 72 nm. Such a long-repeated distance of the lamellar phase was unique in the surfactant system. Moreover, the various structures, such as multilamellar vesicles and branched-like layers, were observed, which suggested that they might be deformable. On the other hand, only core-shell particles were observed in GET6BG20, the core of which was an L₃ phase. GET6BG20 and GET6BG60 significantly enhanced the skin permeation of the hydrophilic model drug, antipyrine (ANP) (log K_o/w, - 1.51). However, their permeation profiles were distinct. Liquid chromatography-tandem mass spectrometry revealed that epidermal accumulation of GEIS was significantly higher with GET6BG60 than GET6BG20 after 1.5 h of permeation, which might be attributed to differences in their deformable properties. Furthermore, GEIS was reported to affect intercellular lipids. Accumulated GEIS in the epidermis may have interacted with intercellular lipids and enhanced the transdermal delivery of ANP. The difference in the permeation profiles of ANP may be attributed to the penetration process of GEIS in the epidermis. This study suggests that GET6BG20 and GET6BG60 are unique carriers to enhance the permeation of hydrophilic drugs, such as ANP.

Effects of Physicochemical Properties of Constituent Ions of Ionic Liquid on Its Permeation through a Silicone Membrane

Ionic liquids (ILs), defined as liquid salts composed of anions and cations, have the advantage of allowing constituent ions to be stably absorbed through biological membranes, such as skin. However, limited information is currently available on the effects of the physicochemical properties of constituent ions on the membrane permeation of ILs. Therefore, we herein investigated the effects of the polarity of constituent cations on the membrane permeation of each constituent ion from IL. Various ILs were prepared by selecting lidocaine (LID) as a cation and a series of p-alkylbenzoic acids with different n-octanol/water partition coefficients (K_o/w) as anions. These ILs were applied to a skin model, a silicone membrane, and membrane permeability was investigated. The membrane permeabilities of p-alkylbenzoic acids from their single aqueous suspensions were also measured for comparison. The membrane permeability of p-alkylbenzoic acid from the aqueous suspension increased at higher K_o/w. However, the membrane permeability of ILs was similar regardless of the K_o/w of the constituent p-alkylbenzoic acid. Furthermore, the membrane permeability of the counterion LID remained unchanged regardless of the constituent p-alkylbenzoic acid. These results suggest that even when the K_o/w of IL constituents markedly differs, the resulting IL does not affect membrane permeability.

Magnetic Field-Responsive Pulsatile Drug Release Using A Magnetic Fluid

Ferrofluids are colloidal liquids with fine magnetic particles. They change shape and fluidity depending on the magnitude and direction of the external magnetic field. The magnetic field-responsive pulsatile release of a model drug, lidocaine hydrochloride (LID·HCl), was determined using a depot-type injection containing white petrolatum and/or hydrophilic cream with a magnetic fluid in various proportions. Drug release was confirmed using a self-made diffusion cell and the application of a moving magnet at the bottom of the preparation. Magnetic field-responsive LID release was observed only when using the white petrolatum preparation and depended on the concentration of the magnetic fluid. Magnetic field responsiveness was not observed in the preparation with only the hydrophilic cream. A greater magnetic field-responsive release was observed with a combination of white petrolatum and hydrophilic cream than with white petrolatum alone. These results may lead to the development of an injectable formulation that enables pulsatile administration of macromolecular drugs.

Enhancement of skin permeation of fluorescein isothiocyanate-dextran 4 kDa (FD4) and insulin by thermalporation

Thermalporation has gained attention as a physical means to enhance skin permeation by creating micropores in the primary skin barrier, stratum corneum, which allows much higher permeation of middle and high molecular weight biopharmaceuticals. In the present study, a PassPort® system (PS) was used as a thermalporation device, and the obtained change in permeation resistance of drugs was evaluated using a parallel skin permeation-resistance model. In addition, the blood concentration-time profile after topical application of insulin was also investigated with the PS treatment. Fluorescein isothiocyanate-dextran (FD-4) and insulin were used as model middle molecular weight drugs. Micropores created by the PS treatment were measured using an optical microscope. An in vitro skin permeation and an in vivo pharmacokinetics experiments were done with FD-4 and insulin, respectively. Barrier function recovery after the PS treatment was evaluated with changes in the electrical skin resistance. About 960-fold higher skin permeation of FD-4 was observed by PSs treatment (4 milliseconds (ms), 200 micropores/cm²). A gradually increased blood concentration of insulin was observed by the PSs treatment, and the relative bioavailability of insulin was 21.1% compared with subcutaneous injection. Skin resistance value was dramatically decreased immediately after the PS treatment, but its value was turned into the initial one by 12 h. The thermalporation is effective for improving skin permeation of FD-4 and transdermal absorption of insulin. These results suggested that the PS treatment may be utilized to increase the skin permeation of topically applied FD-4 and insulin.

Influence of Polyunsaturated Fatty Acid Intake on Kidney Functions of Rats with Chronic Renal Failure

Arachidonic acid (ARA), an omega-6 (ω-6) polyunsaturated fatty acid (PUFA), is involved in the development and maintenance of renal functions, whereas docosahexaenoic acid (DHA) is an omega-3 (ω-3) PUFA that has anti-inflammatory effects and attenuates nephropathy. However, their effects on the progression of chronic kidney disease (CKD) remain unknown. The aim of this study was to assess the effects of feeding ARA, DHA, and ARA and DHA-containing diets on rats with 5/6 nephrectomized kidneys. Urine and feces were collected every 4 weeks, and the kidneys were collected at 16 weeks after surgery. Urinary albumin (U-ALB) excretion increased gradually with nephrectomy, but the U-ALB excretion was attenuated by feeding the rats with an ARA + DHA-containing diet. Reactive oxygen species (ROS) levels in the kidneys were lower in the ARA + DHA group than in the other groups. At 4 weeks after surgery, the lipid peroxide (LPO) levels in the plasma of the ARA + DHA groups decreased significantly after surgery compared to the control CKD group, but this did not happen at 16 weeks post-surgery. There was a significant negative correlation between LPO levels in the plasma at 4 weeks and creatinine clearance, and a positive correlation with urinary albumin levels. These results suggest that the combination of ARA and DHA inhibit the progress of early stage CKD.

Design and Optimization of Scored Tablets with Concave Surface and Application of Bayesian Estimation for Solving Scaleup Problem

From the viewpoint of self-medication, it is valuable to develop patient-friendly scored tablets that possess dividing uniformity. In this context, we attempted to optimize the preparation conditions for a tablet with a unique shape, such as a concavely curved scored tablet (CCST). Employing a design of experiment and a response surface method incorporating a thin-plate spline interpolation, and a bootstrap resampling technique, the optimal preparation conditions for CCST were successfully developed. To make it possible to scaleup the optimal solution estimated on a trial-scale, a Bayesian estimation was applied. Credible ranges of critical responses in large-scale manufacturing were estimated as a posterior probability from the trial-scale experiment as a prior probability. In terms of the large-scale manufacturing, the possibility of solving the scaleup problem was suggested using Bayesian estimation. Furthermore, a simulation study using a finite element method revealed that strong tensile stresses generated along the tip of the score line in CCST when an outer force was applied to the back surface of CCST. An advantage in dividing uniformity is indicated by the unique shape of CCST.

Improvement of Skin Permeation of Caffeine, a Hydrophilic Drug, by the Application of Water Droplets Provided by a Novel Humidifier Device

Recently, a novel humidifier that sprays water fine droplets equipped with a copolymer, poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT/PSS) was developed. PEDOT/PSS in the humidifier absorbs water from the environment and releases fine water droplets by heating. In the present study, the effect of hydration on the skin barrier, stratum corneum, was first determined by the application of fine water droplets using the humidifier. The skin-penetration enhancement effect of a model hydrophilic drug, caffeine, was also investigated using the humidifier and compared with a conventional water-evaporative humidifier. More prolonged skin hydration effect was observed after application of the fine water droplet release humidifier using PEDOT/PSS than that using a conventional humidifier. In addition, markedly higher skin permeation of caffeine was observed in both infinite and finite dose conditions. Furthermore, higher skin permeation of caffeine from oil/water emulsion containing caffeine was observed in finite dose conditions by pretreatment with the humidifier using PEDOT/PSS. This device can provide water droplets without replenishing water, so it is more convenient for enhancing the skin permeation of chemical compounds from topical drugs and cosmetic formulations.

Effect of Rubbing Application on the Skin Permeation of Active Ingredients from Lotion and Cream

Effect of rubbing application on the skin permeation of a hydrophilic drug caffeine (CAF) and lipophilic drug rhododendrol (RD) from lotion and cream were investigated. Skin permeation of CAF was markedly increased by rubbing action independent of the formulation type. In addition, the skin penetration-enhancement effect was affected by the rubbing direction: rubbing application against the direction of hair growth showed the highest permeation compared with rubbing applications along the direction of hair growth and in a circular pattern on the skin. On the other hand, no enhancement effect was observed by the rubbing actions on the skin permeation of RD, regardless of formulation type. Change in the infundibula orifice size of hair follicles by the rubbing and following skin stretching may be related to the higher skin permeation for CAF. In contrast, high RD distribution into the stratum corneum may be a reason why no enhancement effect was observed by the rubbing action. These results can be helpful to predict safety and effectiveness of topically applied formulations.

Effect of Iontophoresis on the Intradermal Migration Rate of Medium Molecular Weight Drugs

The purpose of the present study was to evaluate whether iontophoresis (IP) accelerates the intradermal migration rate of medium molecular weight drugs. Sodium polystyrene sulfonate (PSA) and fluorescein isothiocyanate-dextran (FD) were used as model medium molecular weight acidic and non-electrolyte drugs, respectively. Low molecular weight acid and non-electrolyte drugs were also used for comparison. Drug-loaded excised split-layered skin (SL skin) was used in the experiment. SL skin was prepared using (i) whole skin was split once, (ii) the drug solution was applied on the lower skin, and (iii) the upper skin was layered onto the lower skin containing the drug solution as in the original skin. The effect of constant-current cathodal or anodal IP was applied to the SL skin, and the time course of the cumulative amount of drug migration from the SL skin through the dermis to the receiver was followed. In cases without IP and with anodal IP, the intradermal migration rates of medium molecular weight drugs were much lower than those of small molecules. The driving force for drug migration was thought to be simple diffusion through the skin layer. In contrast, cathodal IP significantly increased the intradermal migration rate of PSA not but of FD or low molecular weight drugs. This IP-facilitated migration of PSA was probably due to electrorepulsion. These results suggest that IP can be used to increase the intradermal migration of medium molecular weight charged drugs.

Latent Structure Analysis of Wet-Granulation Tableting Process Based on Structural Equation Modeling

Quality by design (QbD) is an essential concept for modern manufacturing processes of pharmaceutical products. Understanding the science behind manufacturing processes is crucial; however, the complexity of the manufacturing processes makes implementing QbD challenging. In this study, structural equation modeling (SEM) was applied to understand the causal relationships between variables such as process parameters, material attributes, and quality attributes. Based on SEM analysis, we identified a model composed of the above-mentioned variables and their latent factors without including observational data. Difficulties in fitting the observed data to the proposed model are often encountered in SEM analysis. To address this issue, we adopted Bayesian estimation with Markov chain Monte Carlo simulation. The tableting process involving the wet-granulation process for acetaminophen was employed as a model case for the manufacturing process. The results indicate that SEM analysis could be useful for implementing QbD for the manufacturing processes of pharmaceutical products.

Use of Silicone Membrane Permeation to Assess Thermodynamic Activities of Ionic Liquids and Their Component Cation and Anion

Ionic liquid (IL) was prepared by mixing lidocaine and ibuprofen as a cation and anion, respectively, at various ratios. We determined the permeation of both compounds from the IL through a silicone membrane selected as a model biological membrane, and mathematically analyzed the permeation data from the viewpoint of the thermodynamic activities of lidocaine, ibuprofen, and the IL. As a result, IL and ibuprofen diffusely permeated through the membrane in the case of applying IL preparations with a molar fraction of ibuprofen of 0.5 or higher. The IL was thought to separate into lidocaine and ibuprofen in the receiver. On the other hand, when applying IL preparations with a molar fraction of lidocaine of 0.5 or higher, IL and lidocaine permeated. The permeation rate of IL itself was maximized when the applied IL was prepared using equimolar amounts of lidocaine and ibuprofen, and it decreased when the fraction of lidocaine or ibuprofen increased by more than 0.5. Their membrane permeation rates increased with an increase in their activity, and no more increase was found when the drugs were saturated in the IL. These membrane permeation profiles reflected well the mathematically calculated ones according to the concept of activity.

A Lipid-Based Depot Formulation with a Novel Non-lamellar Liquid Crystal Forming Lipid

PURPOSE

Non-lamellar liquid crystal (NLLC)-forming lipids have gained attention as a novel component because of their ability to self-assemble upon contact with body fluids. In this study, a novel NLLC-forming lipid, mono-O-(5, 9, 13-trimethyl-4-tetradecenyl) glycerol ester (C17MGE), and a model drug with a middle molecule weight, leuprolide acetate (LA), were used to confirm the usefulness of C17MGE as an excipient for depot formulations with sustained release properties.

METHODS

A self-constructed depot formulation was prepared by mixing C17MGE and different types of phospholipids. The constructed NLLC structure was evaluated using small angle X-ray analysis and cryo-transmission electron microscopy. In vitro release and blood concentration profiles of LA were investigated.

RESULTS

The NLLC structure was confirmed by small angle X-ray analysis. LA release was able to be modified by adding different ratios of various phospholipids to C17MGE. Formulations containing 1, 2-dioleoyl-sn-glycero-3-phosphoglycerol sodium salt with a mixing ratio of 12% or 24% (MDOPG12 or MDOPG24, respectively) exhibited sustained release profiles of LA. In addition, the blood concentration of LA was detected over 21 days or more after administration of MDOPG12, and the absolute bioavailability was calculated to be about 100%.

CONCLUSIONS

A depot formulation using C17MGE was useful to achieve sustained release of LA.

Enhancement of Skin Permeation of a Hydrophilic Drug from Acryl-Based Pressure-Sensitive Adhesive Tape

PURPOSE

Penetration enhancers are necessary to overcome a formidable barrier function of the stratum corneum in the development of topical formulations. Recently, non-lamella liquid crystal (NLLC)-forming lipids such as glycerol monooleate and phytantriol (PHY) are gaining increasing attention as a novel skin permeation enhancer. In the present study, fluorescein sodium (FL-Na) was used as a model hydrophilic drug, and acryl-base pressure-sensitive adhesive (PSA) tape containing NLLC forming lipids, mono-O-(5,9,13-trimethyl-4-tetradecenyl) glycerol ester (MGE) or PHY, was prepared to enhance drug permeation through the skin.

METHODS

A PSA patch containing FL-Na was prepared by mixing FL-Na entrapped in NLLC and acrylic polymer. FL permeation through excised hairless rat skin, and also human skin, was investigated. Changes in lipid structure, folding/unfolding state of keratin in the stratum corneum, and penetration of MGE into the stratum corneum were investigated using confocal Raman microscopy.

RESULTS

Enhanced FL permeation was observed by the application of a PSA patch containing MGE and PHY. Especially, dramatically enhancement effect was confirmed by 15% of MGE contained formulation. Penetration of MGE provided diminished orthorhombic crystal structure and a peak shift of the aliphatic CH₃ vibration of keratin chains toward lower wavenumbers.

CONCLUSION

The present results suggested that the formulation development by adding MGE may be useful for improving the skin permeation of mal-permeable drugs such as hydrophilic drugs.

Effect of Rubbing on the Distribution of Topically Applied Drugs into the Hair Follicles

Rubbing actions are often conducted to apply topical formulations onto the skin. Although rubbing was found to increase the skin permeation of drugs, few reports have revealed whether rubbing enhanced either drug permeation through the stratum corneum (SC) or hair follicles (HFs) pathways, or through both. In the present study, we investigated the effects of rubbing on caffeine (CAF) distribution in the SC and HFs. The effect of rubbing direction on the skin penetration of CAF was also investigated. The skin concentration of CAF and its cumulative permeation amount were increased clearly by rubbing. More than six times higher CAF concentrations in the viable epidermis and dermis were observed 5 min after rubbing application compared with no rubbing. On the other hand, slightly increased CAF concentrations were observed in the SC, suggesting that CAF was delivered through the HF pathway by rubbing. Rubbing against the natural hair direction provided the highest skin permeation as well as skin concentrations. Changes in the morphology of the HF opening area might be related to the enhancement effect. These results may provide useful information to understand the effect of rubbing on the skin permeation of applied drugs.

Enhanced nose-to-brain delivery of tranilast using liquid crystal formulations

Intranasal administration is poised as a competent method in delivering drugs to the brain, because the nasal route has a direct link with the central nervous system bypassing the formidable blood-brain barrier. C₁₇-monoglycerol ester (MGE) and glyceryl monooleate (GMO) as liquid crystal (LC)-forming lipids possess desirable formulation characteristics as drug carriers for intranasally administered drugs. This study investigated the effect of LC formulations on the pharmacokinetics of tranilast (TL), a lipophilic model drug, and its distribution in the therapeutic target regions of the brain in rats. The anatomical biodistribution of LC formulations was monitored using micro-computed tomography tandem in vivo imaging systems. MGE and GMO effectively formed LC with suitable particle size, zeta potential, and viscosity supporting the delivery of TL to the brain. MGE and GMO LC formulations enhanced brain uptake by 10- to 12-fold and 2- to 2.4- fold, respectively, compared with TL solution. The olfactory bulb had the highest TL concentration and fluorescent signals among all the brain regions, indicating a direct nose-to-brain delivery pathway of LC formulations. LC-forming lipids, MGE and GMO, are potential biomaterials in formulations intended for intranasal administration.

Effects of Temperature and Humidity on the Skin Permeation of Hydrophilic and Hydrophobic Drugs

The humidity was a well-known method to hydrate the skin; however, the published data were varied, and systemic experiments in the previous papers were few. Therefore, the in vitro permeation of excised porcine ear skin by drugs with different polarities [aminopyrine (AMP), antipyrine (ANP), methylparaben (MP), and ibuprofen (IP)] was analyzed under a constant skin surface temperature with different temperatures and humidities to reveal the effects of temperature and humidity on the skin permeation enhancement effects. Applied formulations were prepared by mixing the drug and a hydrophilic vehicle containing glycerin. The disposition-distance profiles of water and the humectant glycerin in the stratum corneum were also investigated using confocal Raman microscopy. High absolute humidity (AH) significantly contributed to the high skin penetration of the hydrophilic penetrants AMP, ANP, and MP but not the hydrophobic penetrant IP. An increase in the partition parameter and a decrease in the diffusivity parameter occurred with an increase in AH, independent of drug polarity. Moreover, we found that dew condensation induced by high AH on temperature-controlled skin surface may effectively increase water content and may provide higher glycerin distribution in the skin barrier, the stratum corneum. Increasing the amount of water and hydrophilic vehicles such as glycerin in the stratum corneum may enhance the permeation of hydrophilic penetrants AMP, ANP, and MP. These data suggested a dew condensation on the skin surface induced by high AH at a constant skin surface temperature would be important to enhance hydrophilic penetrants.

Pharmacokinetics and Tissue Distribution of Pilocarpine After Application to Eyelid Skin of Rats

Extending the delivery of drugs into the eyes while reducing systemic bioavailability is of utmost importance in the management of chronic ocular diseases. Topical application onto the lower eyelid skin, as an alternative to eye drops, is seen to be a valuable strategy in the treatment of chronic eye diseases. To elucidate the critical value of delivering drugs in solution onto the eyeball through the eyelid skin, pharmacokinetic studies of pilocarpine were conducted, and the results were verified using a direct pharmacodynamic study in rats. The mean residence time of pilocarpine after topical eyelid application to the eyelid skin, conjunctiva, eyeball, and plasma were 14.9, 8.50, 6.29, and 8.11 h, respectively. Conjunctiva and eyeball concentrations of pilocarpine at 8 h were 80-fold and 8-fold higher after topical eyelid application, respectively, than those for eye drops. Pupillary constriction was sustained over 8 h after topical eyelid application. Topical eyelid skin application exhibited a localized drug absorption and specific drug accumulation in the ocular tissues. Hence, it is rational to prepare topical formulations directed onto the eyelid skin, which is suitable for drugs required for long-term treatment.

Effect of layered application on the skin permeation of a cosmetic active component, rhododendrol

Cosmetics containing rhododendrol (RD) were voluntarily recalled after incidents of leukoderma related to their use. Users reported using up to five different RD-containing products by layered application. In this study, we investigated the effects of layered application, formulations, and their components on the skin permeation of cosmetics containing RD. Experiments were designed to simulate actual in-use conditions, such as varying application volumes, physical mixing of formulations, sequence of cosmetics application and time interval between applications, to establish their effect on the skin permeation of RD. Milk and lotion RD-containing cosmetics (2%), 1% aqueous RD, and preparations of formulation components were applied as the first or second layers as finite doses of 10 or 20 µL/cm². Permeation experiments were performed through excised porcine ear skin using Franz diffusion cells with an effective diffusion area of 1.77 cm². Cosmetics applied by layered application exhibited lower skin permeation of RD compared with a single application despite having the same application dose. High initial volume (20 µL at 0 or 5 sec) did not exhibit any significant reduction in the permeation of RD. Formulations and their components caused varying reductions in RD permeation, probably due to changes in thermodynamic activity of the active component. Layered application, formulation components, application volume, time interval and sequence of application had significant influences on the skin permeation of the active component. Moreover, this study established a method of investigating the influence of formulations and their components on the skin permeation of actives after layered application.

Comparative assessment of 24-hr primary skin irritation test and human patch test data with in vitro skin irritation tests according to OECD Test Guideline 439 (for quasi-drugs in Japan)

The Organisation for Economic Co-operation and Development (OECD) Test Guideline (TG) 439 is an in vitro test method of reconstructed human epidermis (RhE), which was developed for hazard identification of irritating chemicals in accordance with a primary skin irritation test using rabbits with 4-hr exposure. A regulation for quasi-drugs in Japan requires data from primary skin irritation tests using rabbits to undergo 24-hr exposure, and this is used as an evidence for 24-hr closed patch tests in humans. In this study with the same chemicals, primary skin irritation test data using rabbits undergoing 24-hr exposure and a 24-hr occlusive human patch test data were analyzed by comparing the results obtained with four test methods adopted in OECD TG 439. The performances of in vitro test methods showed a positive predictive value of 72.7-85.7% to predict the results of 24-hr primary rabbit skin irritation test knowing that its positive predictive value was 57.1% against humans only. The prediction factors of in vitro test methods were higher for the human patch test data with a sensitivity reaching 60 to 80%. Three surfactants gave false negatives in some of the RhE methods evaluated with the human patch test, but in each case, they were correctly classified as positive when evaluated at double concentration. Therefore, the approach of setting the margin to 2 was effective in eliminating false negatives. This suggests that in vitro test methods are useful for assessing skin irritation potential without animal testing for the application of quasi-drugs in Japan.

Prediction of Skin Permeation of Flurbiprofen from Neat Ester Oils and Their O/W Emulsions

Although many in silico models were reported to predict the skin permeation of drugs from aqueous solutions, few studies were founded on the in silico estimation models for the skin permeation of drugs from neat oil formulations and o/w emulsions. In the present study, the cumulative amount of a model lipophilic drug, flurbiprofen (FP), that permeated through skin was determined from 12 different kinds of ester oils (Q_oil) and an in silico model was developed for predicting the skin permeation of FP from these ester oils. Thus, the obtained Q_oil values were well predicted with the FP solubility in the oils (S_oil), the amount of FP uptake into the stratum corneum (SC_oil) and molecular descriptors of dipolarity/polarizability (π₂^H) and molecular density. This model suggests that the thermodynamic activities of FP both in the formulations and skin are the key factors for predicting the skin permeation of FP from the ester oils. In addition, a high linear relationship was observed in the double-logarithm plots between the Q_oil and the cumulative amount of FP permeated through skin from 20% ester oil in water emulsion (Q_emul20%). Furthermore, the skin permeations of FP from 5 and 10% ester oil in water emulsions, Q_emul5% and Q_emul10%, respectively, were also predicted by the horizontal translation of the y-axis intercept of the liner equation for the relation between the Q_oil and Q_emul20%. These prediction methods must be helpful for designing topical oily and/or o/w emulsion formulations having suitable and high skin permeation rate of lipophilic drugs.

Combined Use of N-Palmitoyl-Glycine-Histidine Gel and Several Penetration Enhancers on the Skin Permeation and Concentration of Metronidazole

N-Palmitoyl-Glycine-Histidine (Pal-GH) is a novel low molecular weight gelator. In our previous report, ivermectin, a lipophilic drug, was effectively delivered to skin tissue after topical application with Pal-GH as a spray gel formulation, and a much higher skin concentration was confirmed than with the administration of a conventional oral formulation. The objective of this study was to increase the skin permeation of metronidazole (MTZ), a hydrophilic drug, after the topical application of Pal-GH gel. An evaluation of the combined effect of chemical penetration enhancers (CPEs), such as isopropyl myristate (IPM), propylene glycol (PG), ethanol, diethylene glycol monoethyl ether, and dimethyl sulfoxide (DMSO), on skin permeation was also conducted. We found that a 5% Pal-GH gel containing 1% MTZ (F5_MTZ) exhibited a 2.7-fold higher MTZ permeation through excised hairless rat skin than its solution. Furthermore, F5_PG-MTZ and F5_IPM-MTZ further increased the skin permeation of MTZ when compared to F5_MTZ. Interestingly, F5_PG-MTZ enhanced the skin penetration of MTZ, although no enhancement effect was observed for an MTZ solution containing PG. Thus, a Pal-GH formulation containing PG and IPM may enhance the skin permeation of MTZ.

Development of Drug-in-Adhesive Patch with a Honeycomb Film as a Backing Layer

Excess stripping of stratum corneum (SC) layers by patch-peeling from the skin surface is one cause of skin irritation. High SC hydration by patch occlusion may also cause skin irritation, although the occlusive technique is preferable to increase the skin permeation of topically applied drugs. In the present study, film having a honeycomb structure was selected as the backing layer of a drug-in-adhesive (DIA) patch to reduce peeling of the SC without losing adhesion force to the skin surface, as well as decreasing the skin permeation of a model drug, tulobuterol. The usefulness of the DIA patch with honeycomb film was evaluated by transepidermal water loss (TEWL) changes, amount of SC removed by patch-peeling, distribution pattern of removed SC on the adhesive layer, and water permeation through the patch. Furthermore, skin permeation and release profiles of tulobuterol from the DIA patch were investigated. Significantly (p<0.05) less TEWL change was observed after removal of the patch with a honeycomb film compared with the conventional pressure-sensitive adhesive patch, and no difference in tulobuterol permeation through skin from the patches was confirmed regardless of the type of backing layer. In addition, a lower amount of SC was removed by the peeling of the patch with a honeycomb film. The results suggest that DIA patches with a honeycomb film as a backing layer may be used to achieve less SC removal without reducing the skin permeation of drugs.

Validation Cytotoxicity Assay for Lipophilic Substances

It is challenging to disperse lipophilic substances in a validated cytotoxicity assay, especially for compounds with log Kow greater than or equal to 5 that may show false negative results. The purpose of this study was to explain the challenges in conducting a cytotoxicity validated test of lipophilic substances: Minthostachys setosa, Pimenta pseudocaryophyllus, and Drimysbrasiliensis essential oils. Additionally, we compared the equivalence of Neutral Red (NR) and 3- (4,5-dimethylthiazol-2-yl) -5- (3- carboxymethoxyphenyl) -2- (4-sulfophenyl) -2H -tetrazolium, inner salt (MTS) in detecting cell viability. The Hydrophile-Lipophile Balance (HLB) technique was used to evaluate the dispersion of essential oils and cytotoxicity in accordance to the guidelines of the OECD / GD 129 validated cytotoxicity assay. We compared the equivalence of vital dyes by TOST equivalence test. According to the results, we demonstrated the possibility of using other ways to disperse the lipophilic substances. Based on the HLB theory, we selected polysorbate 20 as the best solubilizing agent of the essential oils studied in D10 culture medium.

Design of a Topically Applied Gel Spray Formulation with Ivermectin Using a Novel Low Molecular Weight Gelling Agent, Palmitoyl-Glycine-Histidine, to Treat Scabies

Palmitoyl-glycine-histidine (Pal-GH) is a new low molecular weight gelling agent. It exhibits thixotropic behavior, low viscosity, and high dissolving properties for a wide range of hydrophilic to lipophilic drugs. Orally administered ivermectin (IVM) is used to treat scabies. However, this treatment is associated with well-known side effects, thus a study is awaited to search for alternative routes of administration. Although a topical formulation of IVM could be a candidate, it requires whole body application except the head and face for several hours on a daily basis. Therefore, in this study, we prepared a gel spray formulation containing IVM as an approach for application to large skin areas with a single spray application without further contact with the applied formulation. Pal-GH gel spray formulations were prepared from its aqueous solution by a heating and cooling method. Rheological behavior and physical appearance (spraying, spreading ability, volume of spraying, and homogeneity) of the prepared formulations were evaluated. Pal-GH gel with propylene glycol demonstrated impressive rheological properties (typical thixotropic behavior) with high hysteresis area among all the tested Pal-GH gels and spreading ability. The obtained IVM concentration in the skin after topical application of 0.1% IVM-containing Pal-GH formulation onto hairless rats was much higher than the reported therapeutic concentration obtained from oral administration in humans. These results suggested that topical application of IVM using a Pal-GH gel spray formulation could be an alternative to the conventional oral forms for the scabies treatment.

Establishment of an evaluation method to detect drug distribution in hair follicles

Development of an appropriate method to evaluate drug disposition or targeting ability in hair follicles (HFs) is urgently needed in order to develop useful pharmaceutical products with pharmacological effects in HFs. In the present study, a cyanoacrylate biopsy (CB) method was used to measure drug disposition in HFs using a model hydrophilic drug, caffeine (CAF), and a lipophilic drug, 4-butylresorcinol (BR), in excised porcine skin. As a result, the height of HF replicas and the recovery ratio decreased with an increase in the application times of the CB method. HF replicas with a length of approximately 175 µm were obtained using a single application of the CB method. Drug distribution in the HF was detected even 5 min after topical application regardless of the lipophilicity of the drugs, although no drug disposition was observed in the deeper layers of the stratum corneum at the same time (5 min). Furthermore, significantly higher amounts of BR were observed in the stratum corneum and HF, compared with those of CAF. These results suggested that the CB method could be useful to evaluate the safety and efficacy as well as the disposition of topically applied chemicals, especially for HF-targeting drugs.

Prediction of Dissolution Data Integrated in Tablet Database Using Four-Layered Artificial Neural Networks

A large number of dissolution data were measured and integrated into a previously constructed tablet database composed of 14 kinds of compounds as model active pharmaceutical ingredients (APIs) with contents ranging from 10 to 80%. The database has contained physicochemical and powder properties of APIs, together with basic physical attributes of tablets such as the tensile strength and the disintegration time. In order to enhance the value of this database, drug dissolution data are essential to improving key information for designing tablet formulations. A four-layered artificial neural network (4LNN), newly implemented in commercially available software, was employed to predict dissolution data from physicochemical and powder properties of APIs. Our results showed that an excellent model for the prediction of dissolution data was achieved with 4LNN method. The function of 4LNN was appreciably better than that of conventional three-layered model, despite both models adopting the same number of nodes and algorithms for activation functions. Furthermore, linear regression models resulted in poor prediction of dissolution data.

Eyelid skin as a potential site for drug delivery to conjunctiva and ocular tissues

The feasibility of topical application onto the (lower) eyelid skin to deliver hydrophilic and lipophilic compounds into the conjunctiva and ocular tissues was evaluated by comparing with conventional eye drop application. Skin permeation and the concentration of several model compounds, and skin impedance were determined utilizing eyelid skin from hairless rats, as well as abdominal skin in the same animals for comparison. In vitro static diffusion cells were used to assess the skin permeation in order to provide key insights into the relationship between the skin sites and drugs. The obtained results revealed that drug permeation through the eyelid skin was much higher than that through abdominal skin regardless of the drug lipophilicity. Specifically, diclofenac sodium salt and tranilast exhibited approximately 6-fold and 11-fold higher permeability coefficients, respectively, through eyelid skin compared with abdominal skin. Histomorphological evaluation and in vivo distribution of model fluorescent dyes were also examined in the conjunctiva and skin after eyelid administration by conventional microscope and confocal laser scanning microscope analyses. The result revealed that eyelid skin has a thinner stratum corneum, thereby showing lower impedance, which could be the reason for the higher drug permeation through eyelid skin. Comparative evaluation of lipophilic and hydrophilic model compounds administered via the eyelid skin over 8h revealed stronger fluorescence intensity in the skin and surrounding tissues compared with eye drop administration. These results suggested that the (lower) eyelid skin is valuable as a prospective site for ophthalmic medicines.

Potential of Stratum Corneum Lipid Liposomes for Screening of Chemical Skin Penetration Enhancers

The evaluation of effective skin chemical penetration enhancers (CPEs) is a crucial process in the development of transdermal and dermal formulations with the capacity to overcome the stratum corneum barrier. In the present study, we aimed to investigate the potential of stratum corneum lipid liposomes (SCLLs) as an alternative tool for the screening of various types and concentrations of CPEs. SCLLs were prepared using a thin-film hydration technique, and two types of fluorescent probes (sodium fluorescein [FL] or 1,6-diphenyl-1,3,5-hexatriene [DPH] were entrapped separately into SCLLs (FL-SCLL and DPH-SCLL, respectively). FL leakage from SCLLs as well as the fluidity of DPH-SCLLs were determined after incubating with various types of CPEs as a function of their concentrations. The obtained results showed a concentration-dependent relationship for most CPEs both for FL leakage and the fluidity of SCLLs. When observing these data in detail, however, the concentration profiles could be classified into five main categories depending on the mode of action of the CPEs. These results strongly suggest the usefulness of SCLLs for high-throughput screening of effective CPEs as well as the understanding of their possible mode of action, especially in the early stage of skin formulation development.

High-Throughput Screening of Potential Skin Penetration-Enhancers Using Stratum Corneum Lipid Liposomes: Preliminary Evaluation for Different Concentrations of Ethanol

In this study, we developed a technique for high-throughput screening (HTS) of skin penetration-enhancers using stratum corneum lipid liposomes (SCLLs). A fluorescent marker, sodium fluorescein (FL), entrapped in SCLLs was prepared to provide a preliminary evaluation of the effect of different concentrations of ethanol on the disruption effect of SCLLs, which is an alternative for skin penetration-enhancing effects. In addition, SCLLs containing a fluorescent probe (DPH, TMA-DPH, or ANS) were also prepared and utilized to investigate SCLL fluidity. The results using SCLL-based techniques were compared with conventional skin permeation and skin impedance test using hairless rat skin. The obtained correlations were validated between FL leakage, SCLL fluidity with various probes, or skin impedance and increases in the skin permeation enhancement ratio (ER) of caffeine as a model penetrant. As a result, FL leakage and SCLL fluidity using ANS were considered to be good indices for the skin penetration-enhancing effect, suggesting that the action of ethanol on the SC lipid and penetration-enhancing is mainly on the polar head group of intercellular lipids. In addition, this screening method using SCLL could be utilized as an alternative HTS technique for conventional animal tests. Simultaneously, the method was found to be time-saving and sensitive compared with a direct assay using human and animal skins.

Effect of Combination of Low-Frequency Sonophoresis or Electroporation with Iontophoresis on the Mannitol Flux or Electroosmosis through Excised Skin

In vitro permeation studies of mannitol were conducted across excised hairless mouse skin to determine and compare the enhancing effect of electroporation (EP) or sonophoresis (SP) combined with iontophoresis (IP) on the electroosmotic flow, and to analyze the enhancement mechanism of these combined methods. Mannitol flux was utilized as an index for the electroosmotic flow due to its low molecular weight and no electrorepulsion effect. The combination of SP and IP (SP/IP) resulted in an apparent increase of electroosmotic flow (no effect was sometimes observed by SP/IP), while that of EP and IP (EP/IP) had no synergistic enhancing effect on the electroosmosis. Next, the combined effect of tape-stripping (TS) and IP (TS/IP) was examined in a similar manner to clarify the difference between the SP/IP and EP/IP effects on electroosmosis. When the TS number increased from 0 to 3, the electroosmotic flow increased with the TS number. However, no further increase was observed when the TS number became more than 3, and the flow started to decrease when the TS number became 5. The electric charge of the skin surface was then measured after SP or TS application. When SP was applied, the skin surface charge became much more negative and the electroosmotic flow by SP/IP was markedly increased. Thus, an increase in the electroosmotic flow across the skin during IP application can be obtained not by EP and TS, but by SP. The combined use of SP and IP is a promising means for the enhanced skin delivery of non-electrolyte drugs.