Diesel particulate matter permeation into normal human skin and intervention using a topical ceramide formulation.

INTRODUCTION: Diesel particulate matter (DPM) emitted from diesel engines is a major source of air pollutants. DPM is composed of elemental carbon, which adsorbs organic compounds including toxic polycyclic aromatic hydrocarbons (PAH). The skin, as well as airways, are directly exposed to DPM, and association of atopic dermatitis, psoriasis flares, and premature skin aging with air pollutant levels has been documented. In skin, the permeation of DPM and DPM-adsorbed compounds is primarily blocked by the epidermal permeability barrier deployed in the stratum corneum. Depending upon the integrity of this barrier, certain amounts of DPM and DPM-adsorbed compounds can permeate into the skin. However, this permeation into human skin has not been completely elucidated. METHODS: We assessed the permeation of PAHs (adsorbed to DPM) into skin using ex vivo normal (barrier-competent) organ-cultured human skin after application of DPM. Two major PAHs, 2-methylnaphthalene and triphenylene, and a carcinogenic polycyclic aromatic hydrocarbon (PAH), benzo(a)pyrene, all found in DPM, were measured in the epidermis and dermis using liquid chromatography electrospray ionization tandem mass spectrometry. In addition, we investigated whether a topical formulation can attenuate the permeation of DPM into skin. RESULTS: 2-methylnaphthalene, triphenylene and benzo(a)pyrene were recovered from the epidermis. Although these PAH were also detected in the dermis after DPM application, these PAH levels were significantly lower than those found in the epidermis. We also demonstrated that a topical formulation that has the ability to form more uniform membrane structures can significantly suppress the permeation of PAH adsorbed to DPMs into the skin. CONCLUSION: Toxic compounds adsorbed by DPM can permeate even barrier-competent skin. Hence, barrier-compromised skin, such as in atopic dermatitis, psoriasis and xerosis, is even more vulnerable to air pollutants. A properly formulated topical mixture that forms certain membrane structures on the skin surface can effectively prevent permeation of exogenous substances, including DPM, into skin.

Development of Ethylcellulose Microparticles for Taste Masking of Fexofenadine.

For taste masking of fexofenadine hydrochloride (FXD), ethylcellulose (EC) microparticles with FXD were developed. The amounts of EC, Tween 80, and polyvinyl alcohol (PVA) in the composition had little effect on initial drug release properties. Based on the results of the drug recovery and the drug release properties, FXD(EC200) was the optimal FXD microparticle formulation. From the results of Fourier transform infrared spectroscopy spectra and X-ray diffraction patterns of FXD(EC200), FXD amorphization in the microparticles and interaction between FXD and other components were suggested, and the formation of a solid dispersion of FXD was suggested. Because the possibility of the complex of PVA and FXD on the particle surface was suggested, sodium lauryl sulfate (SLS) was added to the composition. The initial drug release from FXD microparticles with SLS was further suppressed compared with FXD(EC200). From these results, FXD microparticles with SLS can be prepared as a controlled-release formulation and are expected to be useful for masking the bitter tasting particulates.

Promoting Activity of Terpenes on Skin Permeation of Famotidine.

Famotidine (FMT) is a competitive histamine-2 (H2) receptor antagonist that inhibits gastric acid secretion for the treatment of Gastroesophageal reflux disease. To study the promoting effect and mechanism of terpenes, including l-menthol, borneol, and geraniol, as chemical enhancers, FMT was used as a model drug. Attenuated total reflectance-Fourier transform IR spectroscopy (ATR-FTIR) and differential scanning calorimetry (DSC) were used to explore the effects of terpenes on the skin. Hairless mouse skin was mounted on Franz-type diffusion cell, and skin permeation experiment of FMT hydrogel was carried out. The results suggested that the thermodynamic activity influenced the permeability of the drug, and the main mechanism of terpenes to enhance skin permeation of the drug was based on increasing the fluidity of the intercellular lipids. Moreover, it was revealed that l-menthol simultaneously relaxed the packing structure and lamellar structure, whereas geraniol had a great influence on the lamellar structure only. Collectively, all terpenes had a promoting effect on skin permeation of FMT, indicating their potential as chemical enhancers to change the microstructure of stratum corneum and improve the permeation of FMT through the skin, and it has great potential to be used in transdermal formulations of FMT.

Distribution of Domains Formed by Lateral Packing of Intercellular Lipid in the Stratum Corneum.

Intercellular lipids fill the interstices of corneocytes and serve a barrier function. The amount of transdermal water evaporation varies depending on the packing structure of intercellular lipids, as this structure is important for maintaining barrier efficacy. This packing structure consists of a mixture of crystals (orthorhombic and hexagonal) and liquid crystals (fluid phase), and the proportion of these phases is thought to affect barrier function. However, there have been no methods to visualize the actual distribution of the domains formed by packing structure in intercellular lipids. In this study, the planar distribution of intercellular lipid structures was determined using focal plane array (FPA)-based Fourier transform (FT) IR imaging analysis of stratum corneum cell units obtained by grid stripping. The lipid composition of ceramides was revealed by electrospray ionization tandem mass spectrometry (ESI-MS/MS)-based shotgun lipidomics. The distribution of domains formed by packing structures and the lipid composition of ceramides was compared in skin with high- or low-transepidermal water loss (TEWL). The orthorhombic proportion was lower in high-TEWL skin than in low-TEWL skin. ESI-MS/MS-based shotgun lipidomics analysis showed that the alpha-hydroxyceramide content in the low- and high-TEWL groups differed regarding the distribution of fatty acid chain lengths. The evaluation of stratum corneum cell units using FPA-based FTIR imaging is an innovative technology that can visualize the distribution of domains formed by intercellular lipid-packing structures. Increased proportions of alpha-hydroxyceramide subclasses such as alpha-hydroxy-sphingosine ceramide and alpha-hydroxy-phytosphingosine ceramide were associated with a reduced proportion of the orthorhombic packing structure domain.

Effects and Mode of Action of Oleic Acid and Tween 80 on Skin Permeation of Disulfiram.

Oral disulfiram (DSF) has been used clinically for alcohol dependence and recently has been found to have antitumor activity. A transdermal delivery system would be useful for maintaining drug concentration and reducing the frequency of administration of DSF for cancer treatment. Penetrating the stratum corneum (SC) barrier is a challenge to the transdermal delivery of DSF. Therefore, we investigated the promoting effects and mechanism of action of the combination of oleic acid (OA) and Tween 80 on the skin permeation of DSF. Hairless mouse skin was exposed to OA and Tween 80, combined in various ratios (1 : 0, 2 : 1, 1 : 1, 1 : 2, and 0 : 1). A permeation experiment was performed, and total internal reflection IR spectroscopic measurements, differential scanning calorimetry, and synchrotron radiation X-ray diffraction measurements were taken of the SC with each applied formulation. The combination of OA and Tween 80 further enhanced the absorption-promoting effect of DSF, compared with individual application. The peak of the CH2 inverse symmetric stretching vibration near the skin surface temperature was shifted by a high frequency due to the application of OA, and DSF solubility increased in response to Tween 80. We believe that the increased fluidity of the intercellular lipids due to OA and the increased solubility of DSF due to Tween 80 promoted the absorption of DSF. Our study clarifies the detailed mechanism of action of the skin permeation and promoting effect of DSF through the combined use of OA and Tween 80, contributing to the development of a transdermal preparation of DSF.

Amino Acids and Their N-Acetylated Derivatives Maintain the Skin's Barrier Function.

The hydrocarbon-chain packing structure of intercellular lipids in the stratum corneum (SC) is critical to the skin's barrier function. We previously found that formation of V-shaped ceramide reduces the barrier function of skin. There are few agents, apart from ceramides and fatty acids that can improve the orthorhombic packing (Orth) ratio of the intercellular lipid packing structure. In this study, we investigated agents that directly increase the Orth ratio. We selected an intercellular lipid model consisting of ceramide, cholesterol, and palmitic acid and performed differential scanning calorimetry. We focused on natural moisturizing factor components in the SC, and therefore investigated amino acids and their derivatives. The results of our intercellular lipid model-based study indicate that N-acetyl-L-hydroxyproline (AHYP), remarkably, maintains the lamellar structure. We verified the effect of AHYP on the lamellar structure and hydrocarbon chain packing structure of intercellular lipids using time-resolved X-ray diffraction measurements of human SC. We also determined the direct physicochemical effects of AHYP on the Orth ratio of the hydrocarbon-chain packing structure. Hence, the results of our human SC study suggest that AHYP preserves skin barrier function by maintaining the hydrocarbon-chain packing structure of intercellular lipids via electrostatic repulsion. These findings will facilitate the development of skincare formulation that can maintain the skin's barrier function.

Manufacturability and Properties of Granules and Tablets Using the Eco-Friendly Granulation Method Green Fluidized Bed Granulation Compared to Direct Compression.

This study aimed to compare the manufacturability and granule and tablet properties of green fluidized bed granulation (GFBG) and of direct compression (DC). Acetaminophen was used as a low compactability model drug. The process time of GFBG to produce final mixtures was comparable to that of DC, and thus GFBG could be considered a simple process. DC could not produce 30% drug load tablets owing to poor granule flowability, whereas no problems were observed in the GFBG tableting process up to 80% of drug load. Tablets prepared with GFBG showed higher tensile strength than those prepared using DC. Compactability evaluation results show that the yield pressure of the granules prepared with GFBG was significantly lower than that of DC, suggesting that the granules prepared with GFBG were easily plastically deformed. Moreover, tablets prepared with GFBG showed fast disintegration, which was faster than that of DC. We conclude that GFBG produces granules with higher drug content and desired physicochemical properties at low cost.

Phase Separation in Lipid Lamellae Result from Ceramide Conformations and Lateral Packing Structure.

Intercellular lipids in the stratum corneum protect the living body from invasion by allergens and pathogens, and also suppresses water evaporation within the body. It is important to understand how differences in the microstructure of intercellular lipids arise. This microstructure is affected by lipid composition. Studies using intercellular lipid models have reported the formation of two phases with different short lamellar periodicities. However, the details of the packing structure characteristics of the two phases observed in these intercellular lipid models are unclear. Our previous report revealed that different short periodicity phases coexist in the N-(α-hydroxyoctadecanoyl)-dihydrosphingosine (CER[ADS]), cholesterol (CHOL), and palmitic acid (PA) complex model. In this study, the characteristics of the packing structure of two phases with different short lamellar periodicities, which were observed in the intercellular lipid model (CER[ADS]/CHOL/PA) that we used previously, were adjusted for models with different lipid compositions. The characteristics of the packed and lamellar structures have been determined by temperature-scanning small-angle X-ray scattering and wide-angle X-ray diffraction measurements simultaneously. These differences in lamellar structure were thought to be caused by differences in ceramides (CER) conformation between the hairpin and the V-shape type. The lamellar structure of the V-shaped CER conformation has a low orthorhombic ratio. The above results suggest that an increase in the ratio of CER with the V-shaped structure causes the lamellar structure to have low orthorhombic ratio, thereby contributing to a decrease in the bilayer's barrier function.

The Usefulness of Definitive Screening Design for a Quality by Design Approach as Demonstrated by a Pharmaceutical Study of Orally Disintegrating Tablet.

Definitive screening design (DSD) is a new class of small three-level experimental design that is attracting much attention as a technical tool of a quality by design (QbD) approach. The purpose of this study is to examine the usefulness of DSD for QbD through a pharmaceutical study on the preparation of ethenzamide-containing orally disintegrating tablet. Model tablets were prepared by directly compressing the mixture of the active pharmaceutical ingredient (API) and excipients. The five evaluated factors assigned to DSD were: the contents of API (X1) and lubricant (X2), and the compression force (X3) of the tableting process, the mixing time (X4), and the filling ratio of powder in the V-type mixer (X5). After tablet preparation, hardness and disintegration time were measured. The same experiments were performed by using the conventional design of experiments [i.e., L8 and L16 orthogonal array designs and central composite design (CCD)]. Results showed that DSD successfully clarified how various factors contribute to tablet properties. Moreover, the analysis result from DSD agreed well with those from the L8 and L16 experiments. In additional experiments, response surfaces for tablet properties were created by DSD. Compared with the response surfaces created by CCD, DSD could produce reliable response surfaces for its smaller number of experiments. We conclude that DSD is a powerful tool for implementing pharmaceutical studies including the QbD approach.

Time-temperature superposition principle for the kinetic analysis of destabilization of pharmaceutical emulsions.

The time-temperature superposition principle (TTSP) was applied to the destabilization kinetics of a pharmaceutical emulsion. The final goal of this study is to predict precisely the emulsion stability after long-term storage from the short-period accelerated test using TTSP. As the model emulsion, a cream preparation that is clinically used for the treatment of pruritus associated with chronic kidney disease was tested. After storage at high temperatures ranging from 30 to 45 °C for designated periods, the emulsion state was monitored using magnetic resonance imaging, and then the phase separation behaviors observed were analyzed according to the Arrhenius approach applying TTSP. The Arrhenius plot showed a biphasic change around 35 °C, indicating that the separation behaviors of the sample were substantially changed between the lower (30-35 °C) and higher (35-45 °C) temperature ranges. This study also monitored the coalescence behavior using a backscattered light measurement. The experiment verified that the destabilization was initiated by coalescence of oil droplets and then it eventually led to obvious phase separation via creaming. Furthermore, we note the coalescence kinetics agreed well with the phase separation kinetics. Therefore, in the case of the sample emulsion, the coalescence behavior has a dominant influence on the destabilization process. This study offers a profound insight into the destabilization process of pharmaceutical emulsions and demonstrates the promising applicability of TTSP to pharmaceutical research.

MRI Monitoring of the Mixed State of Admixtures Consisting of Moisturizing Cream and Steroid Ointment during the Mixing Process by a Revolution/Rotation-Type Hybrid Mixer.

The admixture of a steroid ointment and a moisturizing cream is frequently prescribed to patients suffering from atopic dermatitis. For the mixing operation, a revolution/rotation-type hybrid mixer is widely used in pharmacy. The purpose of this study was to monitor the mixed state of the admixtures during the mixing process of the hybrid mixer. The key technology used in this study was magnetic resonance imaging (MRI). Two different commercial mometasone furoate-containing ointments were used as a test steroid ointment. After layering the moisturizing cream and the steroid ointment in an ointment bottle, the sample was mixed for a predetermined period using the hybrid mixer. According to MRI transverse relaxation time (T2) mapping for nondestructive monitoring, it was confirmed that the Flumeta® ointment-containing admixture became homogeneous by mixing for 60 s or more. As for the mometasone furoate ointment 0.1%-containing admixture, the mixed state, after becoming homogeneous, was separated into two layers again by the prolonged mixing process. From the 1H-NMR spectra of the phase-separated layers, re-separation was caused by removing aqueous components from the bottom of the samples. MRI is a powerful tool for monitoring the mixed state of the admixture during the mixing process. We believe that our findings offer profound insights into the clinical practice of the mixing operation using a hybrid mixer.

Nondestructive Monitoring of the Dispersion State of Titanium Dioxide Nanoparticles in Concentrated Suspensions Using Magnetic Resonance Imaging.

The purpose of the present study is to demonstrate the applicability of magnetic resonance imaging, especially T2 relaxation time mapping, for nondestructive monitoring of the dispersion state of nanoparticles (NPs) in concentrated suspensions. TiO2 15-nm-diameter NPs, for use in sunscreen lotion products, were examined as a test NP. First, this study investigated whether T2 is sensitive to the NP concentration. In experiments with pulsed nuclear magnetic resonance on TiO2 NP suspensions with different organic solvents (ethanol, acetone, and decamethylcyclopentasiloxane), the T2 of each solvent varied in the suspensions according to the NP concentration. This study also confirmed that T2 mapping was effective for visualizing differences in NP concentration. Subsequently, gravitational sedimentation of the test suspensions was investigated. T2 mapping exhibited better detection sensitivity to sedimentation occurring in concentrated suspensions than visual observation, as it enabled the detection of changes in NP distributions that could not be visible to the naked eye. In addition, measurements of backscattered light enabled the full understanding of the dispersion stability of the TiO2 NPs in each solvent. Finally, the present study evaluated the centrifuge sedimentation of a commercial TiO2 NP suspension. T2 mapping clearly showed the complicated sedimentation behavior induced by the centrifugation treatment. The simulated fluid flow was consistent with the particle distribution in the centrifuged sample; thus, the sedimentation was believed to have developed in accordance with the vorticity generated by the centrifugation.

Strength Simulation of Scored Tablets Based on the Finite Element Method Using an Extreme Vertices Design.

The mechanical strain distribution of scored tablets was simulated using the finite element method (FEM). The score was fabricated as a triangular runnel with the pole on the top surface of flat tablets. The effect of diametral compression on the tablet surface strain was evaluated by changing the angle between the scored line and the diametral compression axis. Ten types of granules were prepared according to an extreme vertices design. Young's modulus and the Poisson ratio for the model powder bed were measured as elastic parameters. The FEM simulation was then applied to the scored tablets represented as a continuous elastic model. Strain distributions in the inner structure of the tablets were simulated after the application of external force. The maximum principal strain (ε1) value was obtained with tablets containing a large amount of corn starch, in all scored line positions. In contrast, the ε1 value of the tablets containing a large amount of microcrystalline cellulose was minimal. The adequacy of the simulation was evaluated by experiments with scored tablets. The results indicated a fairly good agreement between the FEM simulation and experiments. Moreover, it was found that the ε1 value correlated negatively with the value of tablet hardness. These results suggest that the FEM simulation was advantageous for designing scored tablets.

Enhancement of Galantamine HBr Skin Permeation Using Sonophoresis and Limonene-Containing PEGylated Liposomes.

This study aimed to investigate the effect of low-frequency sonophoresis (SN) and limonene-containing PEGylated liposomes (PL) on the transdermal delivery of galantamine HBr (GLT). To evaluate the skin penetration mechanism, confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) were employed. The application of SN led to more GLT penetration into and through the skin than GLT solution alone. The liposomes also improved GLT permeation, and 2% limonene-containing PL (PL-LI2%) exhibited the highest GLT permeation, followed by PL-LI1%, PL-LI0.1%, and PL. The CLSM images of PL-LI2% resulted in the highest fluorescence intensity of fluorescent hydrophilic molecules in the deep skin layer, and the rhodamine PE-labeled liposome membrane was distributed in the intercellular region of the stratum corneum (SC). PL-LI2% induced significant changes in intercellular lipids in the SC, whereas SN had no effect on intercellular lipids of the SC. DSC thermograms showed that the greatest decrease in the lipid transition temperature occurred in PL-LI2%-treated SC. SN might improve drug permeation through an intracellular pathway, while limonene-containing liposomes play an important role in delivering GLT through an intercellular pathway by increasing the fluidity of intercellular lipids in the SC. Moreover, a small vesicle size and high membrane fluidity might enhance the transportation of intact vesicles through the skin.

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.

The Introduction of an Active Rest Program by Workplace Units Improved the Workplace Vigor and Presenteeism Among Workers: A Randomized Controlled Trial.

OBJECTIVE: The present study was designed to examine the effects of active rest by workplace units on not only workers' individual vigor but also workplace vigor and presenteeism. METHODS: A total of 130 workers performed our active rest (short-time exercise) program for 10 minutes per day during their lunch breaks, three to four times per week for 8 weeks. Subjects from a workplace unit were randomly allocated to the intervention (n = 66) or control (n = 64) groups. The participants' work engagement and Work Functioning Impairment Scale (WFun) were examined at the baseline and after the 8-week intervention period. RESULTS: After 8 weeks, the intervention group showed improved "vigor" values in work engagement and WFun (P < 0.05). CONCLUSION: These results suggest that the introduction of active rest program by workplace units provides a viable means for improving workplace vigor and presenteeism.

Determination of Density Distribution of Tablets Using Synchrotron X-ray Computed Tomography.

The purpose of this study was to determine the density distribution of scored and round-faced tablets using synchrotron X-ray computed tomography. The tablets were made by direct compression of standard formulations. The density distribution of scored flat-faced tablets was uniform in the whole cross-sectional image. However, the tablet formulated using microcrystalline cellulose (MCC) was very dense at the tip of the score only. It is caused by the poor fluidity of MCC particles. In the case of round-faced tablets, the density in the central section of the tablet was relatively low, compared with those of peripheral areas. These observations correlated well with the results obtained by the finite element method simulation using appropriate material models.

Molecular Interaction between Intercellular Lipids in the Stratum Corneum and l-Menthol, as Analyzed by Synchrotron X-Ray Diffraction.

l-Menthol increases drug partitioning on the surface of skin, diffusion of drugs in the skin, and lipid fluidity in the stratum corneum and alters the rigidly arranged lipid structure of intercellular lipids. However, l-menthol is a solid at room temperature, and it is difficult to determine the effects of l-menthol alone. In this study, we vaporized l-menthol in order to avoid the effects of solvents. The vaporized l-menthol was applied to the stratum corneum or lipid models comprising composed of ceramides (CER) [EOS], the longest lipid acyl chain of the ceramides in the stratum corneum lipids that is associated with the barrier function of the skin; CER [NS], the shorter lipid acyl chain of the ceramides, and the most components in the stratum corneum of the intercellular lipids that is associated with water retention in the intercellular lipid structure of the stratum corneum; cholesterol; and palmitic acid. Synchrotron X-ray diffraction, differential scanning calorimetry, and attenuated total reflection Fourier transform infrared spectroscopy analyses revealed that the lipid models were composed of hexagonal packing and orthorhombic packing structures of different lamellar periods. Taken together, our results revealed that l-menthol strongly affected the lipid model composed of CER [EOS]. Therefore, l-menthol facilitated the permeation of drugs through the skin by liquid crystallization of the longer lamellar structure. Importantly, these simple lipid models are useful for investigating microstructure of the intercellular lipids in the stratum corneum.

Effect of Nerolidol and/or Levulinic Acid on the Thermotropic Behavior of Lipid Lamellar Structures in the Stratum Corneum.

Permeation enhancers are required to deliver drugs through the skin efficiently and maintain effective blood concentrations. Studies of the barrier function of the stratum corneum using l-menthol, a monocyclic monoterpene widely used in medicines and foods, have revealed an interaction between characteristic intercellular lipid structures in the stratum corneum and permeation enhancers. The variety of permeation enhancers that can be used to contribute to transdermal delivery systems beyond l-menthol is increasing. In this study, we focused on nerolidol and levulinic acid and investigated their influence on stratum corneum lipid structures. Nerolidol, a sesquiterpene, has been reported to enhance the permeation of various drugs. Levulinic acid is reported to enhance the permeability of buprenorphine and is used as a component of the buprenorphine® patch. Synchrotron X-ray diffraction and attenuated total reflectance Fourier transform IR spectroscopy measurements revealed that nerolidol disturbs the rigidly arranged lipid structure and increases lipid fluidity. Levulinic acid had a smaller effect on stratum corneum lipid structures, but did increase lipid fluidity when co-administered with nerolidol or heat. We found that nerolidol has an effect on stratum corneum lipids similar to that of l-menthol, and levulinic acid had an effect similar to that of oleic acid.

Effect of Surfactants and Thickeners on the Stability of Menthol-Diphenhydramine Cream Identified by Magnetic Resonance Imaging.

A menthol-diphenhydramine cream is prepared in hospital pharmacies and then prescribed to patients for the treatment of pruritus associated with chronic kidney disease. The purpose of this study is to design a stable formulation without any concern about phase separation during its clinical use on patients. As a preventive measure against phase separation, various surfactants and thickeners were incorporated into the creams. The test creams were stored at 40°C, and then their phase separation behaviors were monitored. The key technology was magnetic resonance imaging T2 mapping. From the T2 maps, some surfactants showed a certain stabilizing effect. In addition, the data analysis using Kohonen's self-organizing map revealed that hydrophilic-lipophilic balance of the surfactant is an important factor for the stabilizing effects of the surfactants. However, as a whole, the effect of surfactant was not sufficient to improve completely the low stability. By contrast, the creams were significantly stabilized by addition of thickeners. In particular, the stabilizing effect of carbomer Hiviswako105® (H105) was very high; no phase separation was observed from the cream containing H105 even after 30 d storage at 40°C. This study also verified the combination effect of surfactants and thickeners on the improvement of the emulsion stability. In conclusion, we successfully established a stable formulation of menthol-diphenhydramine cream.