Methods to simulate rubbing of topical formulation for in vitro skin permeation studies

Traditional Scraping (Gua Sha) Combined with Copper-Curcumin Nanoparticle Oleogel for Accurate and Multi-Effective Therapy of Androgenic Alopecia

Androgenetic alopecia (AGA) is a prevalent systemic disease caused by diverse factors, for which effective treatments are currently limited. Herein, the oleogel (OG) containing copper-curcumin (CuR) nanoparticles is developed, designated as CuRG, which is also combined with traditional naturopathic scraping (Gua Sha, SCR) as a multifunctional therapy for AGA. With the assistance of lipophilic OG and SCR, CuR can efficaciously penetrate the epidermal and dermal regions where most hair follicles (HFs) reside, thereby releasing curcumin (CR) and copper ions (Cu2+) subcutaneously to facilitate hair regeneration. Concomitantly, the mechanical stimulation induced by SCR promotes the formation of new blood vessels, which is conducive to reshaping the microenvironment of HFs. This study validates that the combination of CuRG and SCR is capable of systematically interfering with different pathological processes, ranging from improvement of perifollicular microenvironment (oxidative stress and insufficient vascularization), regulation of inflammatory responses to degradation of androgen receptor, thus potentiating hair growth. Compared with minoxidil, a widely used clinical drug for AGA therapy, the designed synergistic system displays augmented hair regeneration in the AGA mouse model.

Effect of massage on retinol skin penetration

Topical administration of active substances may be promoted by optimizing not only the vehicle formulation but also the application protocol. The formulation aspects are widely studied in the literature while a few works are dedicated to the development of application methods. In this context, we studied an application protocol usable as a part of skincare routine by investigating the effect of massage on the skin penetration of retinol. Retinol is a lipophilic molecule widely used as an anti-ageing firming agent in cosmetic formulations. Massage was applied to pig skin explants mounted to Franz diffusion cells after or before the deposit of the retinol-loaded formulation. Thetype of skin massage (roll or rotary type) and its duration were varied.The massage protocol had a significant influence on retinol skin penetration. Due to its highly lipophilic character, retinol accumulated into the stratum corneum but, depending on the massage protocol, a significant retinol concentration was obtained after 4 hours in epidermis and dermis layers. Results showed that the roll-type massage was significantly more efficient than the rotary process that exhibited little effect on retinol cutaneous penetration. Such results could be interesting for the development of massage devices in association with cosmetic formulations.

Sublimation of Drugs from the Site of Application of Topical Products

The objective of the project was to investigate the plausibility of active pharmaceutical ingredients (APIs) to undergo sublimation from topical application following evaporation of solvent. Topical formulations with different APIs were subjected to a sublimation screening test. The APIs in the selected topical products were found to undergo sublimation to a different extent. The salicylic acid topical product was found to undergo a significant loss due to sublimation. The extent of sublimation of salicylic acid was significantly greater at skin temperature compared to room temperature. When the APIs were subjected to the sublimation screening test in their neat form at 32 ± 1 °C, the natural log of the rate of sublimation decreased linearly with the standard enthalpy of sublimation of compound (R² = 0.89). The formulation composition was found to have a significant impact on the extent of sublimation of the representative API, salicylic acid. The sublimation of APIs from the topical product was found to affect the mass balance studies in the case of the salicylic acid ointment. Furthermore, the results of the human studies agreed with the in vitro experimental results demonstrating the plausibility of loss of API due to sublimation from the site of application.

Does skin permeation kinetics influence efficacy of topical dermal drug delivery system?: Assessment, prediction, utilization, and integration of chitosan biomacromolecule for augmenting topical dermal drug delivery in skin

Skin permeation is an integral part of penetration of topical therapeutics. Zero order in addition to Higuchi permeation kinetic is usually preferred in topical drug delivery cargo. Penetration of therapeutic entities through epidermal barrier is a major challenge for scientific fraternity. Furthermore, penetration of therapeutic entities determines the transportation and ultimately therapeutic efficacy of topical dermal dosage forms. Apart from experimentation models, mathematical equations, in silico docking, molecular dynamics (MDs), and artificial neural network (Neural) techniques are being used to assess free energies and prediction of electrostatic attractions in order to predict the permeation phenomena of therapeutic entities. Therefore, in the present review, we have summarized the significance of kinetic equations, in silico docking, MDs, and ANN in assessing and predicting the penetration behavior of topical therapeutics through dermal dosage form. In addition, the role of chitosan biomacromolecule in modulating permeation of topical therapeutics in skin has also been illustrated using computational techniques.

Recent advances in mechanical force-assisted transdermal delivery of macromolecular drugs

The transdermal delivery of macromolecular drugs has become one of the focused topics in pharmaceutical research since it enables highly specific and effective delivery, while avoiding the pain and needle phobia associated with injection, or incidences like drug degradation and low bioavailability of oral administration. However, the passive absorption of macromolecular drugs via skin is highly restricted by the stratum corneum owing to high molecular weight. Therefore, various strategies have been extensively developed and conducted to facilitate the transdermal delivery of macromolecular drugs, among which, mechanical force-assisted techniques occupy dominant positions. Such techniques include ultrasound, needle-free jet injection, temporary pressure and microneedles. In this review, we focus on recent transdermal enhancing strategies utilizing mechanical force, and summarize their mechanisms, advantages, limitations and clinical applications respectively.

Cutaneous Pharmacokinetics of Acyclovir Cream 5% Products: Evaluating Bioequivalence with an In Vitro Permeation Test and an Adaptation of Scaled Average Bioequivalence

PURPOSE

The in vitro permeation test (IVPT) with a new statistical approach was investigated to evaluate the utility of an IVPT methodology as a sensitive tool to support a demonstration of bioequivalence (BE) for topical dermatological drug products.

METHODS

IVPT experiments were performed utilizing ex vivo human skin. The initial screening tests involved four differently formulated acyclovir 5% creams: the U.S. Zovirax® as the reference product and the U.K. Zovirax®, Aciclovir 1A Pharma® and Aciclostad® as test products. Subsequently, a pivotal BE study was conducted comparing the two Zovirax® creams. The resulting data was used to evaluate BE of test (T) versus reference (R), T versus T, and R versus R, with an adaption of scaled average BE approach to address high variability in IVPT data.

RESULTS

More acyclovir permeated into and through the skin from the two Zovirax® creams compared to the two non-Zovirax® creams. The U.S. Zovirax® cream showed a significantly higher J_max and total amount permeated over 48 h, compared to the U.K. Zovirax® cream. The statistical analysis indicated that the test and reference products were not bioequivalent, whereas each product tested against itself was shown to be bioequivalent.

CONCLUSIONS

The current study demonstrated that the IVPT method, with an appropriate statistical analysis of the results, is a sensitive and discriminating test that can detect differences in the rate and extent of acyclovir bioavailability in the skin from differently formulated cream products.

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.

Rheology by Design: A Regulatory Tutorial for Analytical Method Validation

The increasing demand for product and process understanding as an active pursuit in the quality guideline Q8 and, more recently, on the draft guideline on quality and equivalence of topical products, has unveiled the tremendous potential of rheology methods as a tool for microstructure characterization of topical semisolid dosage forms. Accordingly, procedure standardization is a dire need. This work aimed at developing and validating a methodology tutorial for rheology analysis. A 1% hydrocortisone cream was used as model cream formulation. Through a risk assessment analysis, the impact of selected critical method variables (geometry, temperature and application mode) was estimated in a broad range of rheological critical analytical attributes-zero-shear viscosity, upper-shear thinning viscosity, lower-shear thinning viscosity, infinite-shear viscosity, rotational yield point, thixotropic relative area, linear viscoelastic region, oscillatory yield point, storage modulus, loss modulus, and loss tangent. The proposed validation of the approach included the rheometer qualification, followed by the validation of numerous operational critical parameters regarding a rheology profile acquisition. The thixotropic relative area, oscillatory yield point, flow point and viscosity related endpoints proved to be highly sensitive and discriminatory parameters. This rationale provided a standard framework for the development of a reliable and robust rheology profile acquisition.

Vulnerability of the skin barrier to mechanical rubbing

Skin barrier function is the battlefront for preventing permeation of harmful substances and infectious diseases. However, it can be destroyed by mechanical forces, as shown in many studies. Excess rubbing may increase the permeability of the skin to aqueous material. Although the skin barrier plays an important physiological role in humans, the vulnerability of skin to mechanical rubbing is poorly understood. Therefore, we investigated the effects of rubbing on the skin in vitro; skin damage was quantified by laser-induced fluorescence. Microscopic observation showed that keratinocytes in the stratum corneum sustained traumatic damage, which reduced the barrier function in that region. The permeability of the skin to an aqueous solution increased with rubbing frequency and load, and rubbing markedly reduced the barrier function of the stratum corneum. To understand the mechanisms underlying the skin damage, we developed a simple mathematical model assuming that the skin is a viscoelastic material. We hypothesized that the increased skin permeability was caused by the damage sustained by keratinocytes in the stratum corneum, and that the permeability was proportional to the time-averaged strain. Our theoretical results showed quantitative agreement with the experimental results and illustrated that rubbing and strain relaxation play key roles in rubbing-induced permeation.

Temporal pressure enhanced topical drug delivery through micropore formation

Transdermal drug delivery uses chemical, physical, or biochemical enhancers to cross the skin barrier. However, existing platforms require high doses of chemical enhancers or sophisticated equipment, use fragile biomolecules, or are limited to a certain type of drug. Here, we report an innovative methodology based on temporal pressure to enhance the penetration of all kinds of drugs, from small molecules to proteins and nanoparticles (up to 500 nm). The creation of micropores (~3 μm2) on the epidermal layer through a temporal pressure treatment results in the elevated expression of gap junctions, and reduced expression of occludin tight junctions. A 1 min treatment of 0.28-MPa allows nanoparticles (up to 500 nm) and macromolecules (up to 20 kDa) to reach a depth of 430-μm into the dermal layer. Using, as an example, the delivery of insulin through topical application after the pressure treatment yields up to 80% drop in blood glucose in diabetic mice.

Development of Topical/Transdermal Self-Emulsifying Drug Delivery Systems, Not as Simple as Expected

Self-emulsifying drug delivery systems (SEDDSs) originated as an oral lipid-based drug delivery system with the sole purpose of improving delivery of highly lipophilic drugs. However, the revolutionary drug delivery possibilities presented by these uniquely simplified systems in terms of muco-adhesiveness and zeta-potential changing capacity lead the way forward to ground-breaking research. Contrarily, SEDDSs destined for topical/transdermal drug delivery have received limited attention. Therefore, this review is focused at utilising principles, established during development of oral SEDDSs, and tailoring them to fit evaluation strategies for an optimised topical/transdermal drug delivery vehicle. This includes a detailed discussion of how the authentic pseudo-ternary phase diagram is employed to predict phase behaviour to find the self-emulsification region most suitable for formulating topical/transdermal SEDDSs. Additionally, special attention is given to the manner of characterising oral SEDDSs compared to topical/transdermal SEDDSs, since absorption within the gastrointestinal tract and the multi-layered nature of the skin are two completely diverse drug delivery territories. Despite the advantages of the topical/transdermal drug administration route, certain challenges such as the relatively undiscovered field of skin metabolomics as well as the obstacles of choosing excipients wisely to establish skin penetration enhancement might prevail. Therefore, development of topical/transdermal SEDDSs might be more complicated than expected.

Rheological temperature sweeping in a quality by design approach for formulation development and optimization

Many topical drug products are multi-phase systems which are prone to phase separation exhibiting a high risk for not meeting the critical quality attributes (CQAs) of a pharmaceutical product such as uniform active pharmaceutical ingredient (API) distribution and physical homogeneity. In order to investigate and control these CQAs a rheological temperature sweeping (RTS) method was implemented and refined to enable quantification of these characteristics within a quality by design (QbD) approach. For method implementation, emulsion and ointment compositions were prepared within a design of experiments (DoE) and critical responses from RTS were extracted via principal component analysis (PCA) in a multivariate data analysis (MVA) approach. The span after 3 cycles of RTS on emulsions and a combination of 5 principal components (PCs) for ointments were selected as responses from PCA. The span correlates with the droplet size of selected emulsions followed during stability whereas the combination of the PCs for ointments enables a differentiation of the compositions. Identified critical material attributes (CMAs) are the emulsifier concentration of the emulsion and the liquid paraffin (LP) content of the ointments. In conclusion, RTS enables a rapid screening of liquid and semi-solid products in a quantitative manner for pharmaceutical development and formulation optimization.

Resveratrol-loaded nanoemulsion gel system to ameliorate UV-induced oxidative skin damage: from in vitro to in vivo investigation of antioxidant activity enhancement

In the present study resveratrol nanoemulsion gel was developed and optimized with the aim of enhancing the permeability and antioxidant activity against ultraviolet (UV)-induced oxidative skin damage. Droplet size, polydispersity index, drug permeation flux, permeability coefficient and drug deposition in skin of resveratrol-loaded nanoemulsion were found to be 65.00 ± 5.00 nm, 0.171 ± 0.082, 144.50 μg/cm²/h, 2.90 × 10^-2 cm/h and 45.65 ± 4.76%, respectively, whereas drug permeation flux, permeability coefficient and drug deposition in skin from nanoemulsion gel were found to be 107.70 μg/cm²/h, 2.06 × 10^-2 cm/h and 62.65 ± 4.98%, respectively. Confocal studies depicted deeper penetration of resveratrol from nanoemulsion gel. Differential scanning calorimetry and Fourier-transform infrared spectrophotometer studies confirmed that nanoemulsion gel enhanced fluidization of stratum corneum lipids and conformational disruption of lipid bilayer, thereby enhancing skin permeation of resveratrol. Histopathology study of skin revealed that resveratrol-loaded nanoemulsion gel inhibited UV-induced spongosis, edema and epidermal hyperplasia response. Levels of glutathione, superoxide dismutase, catalase and protein carbonyl in the skin of UV-irradiated rats were significantly (p < 0.01) improved in the skin of animals treated with nanoemulsion gel. Experimental results suggested that nanoemulsion gel could be explored as a promising carrier for topical delivery of resveratrol for prevention of UV-induced oxidative skin damage owing to its enhanced permeability and retention effect.

Biopharmaceutical Development of a Bifonazole Multiple Emulsion for Enhanced Epidermal Delivery

Efficient topical delivery of imidazolic antifungals faces the challenge of overcoming its limited water solubility and its required long-lasting duration of treatments. In this paper, a hydrophilic multiple emulsion (ME) of Bifonazole (BFZ) is shown to maximize its skin retention, minimize its skin permeation, and maintain an acceptable level of being harmless in vivo. The formulations were pharmaceutically characterized and application properties were assessed based on viscosity measurements. Non-Newtonian pseudoplastic shear thinning with apparent thixotropy was observed, facilitating the formulation retention over the skin. The in vitro release profile with vertical diffusion cells showed a predominant square-root release kinetic suggesting an infinite dose depletion from the formulation. Ex vivo human skin permeation and penetration was additionally evaluated. Respective skin permeation was lower than values obtained with a commercial O/W formulation. The combination of amphoteric and non-ionic surfactants increased the bifonazole epidermal accumulation by a factor of twenty. This fact makes the possibility of increasing its current 24 h administration frequency more likely. Eventual alterations of skin integrity caused by the formulations were examined with epidermal histological analysis and in vivo preclinical measurements of skin elasticity and water retrograde permeation. Histological analysis demonstrated that the multiple emulsions were harmless. Additionally, modifications of in vivo skin integrity descriptors were considered as negligible.

Efficient UV Filter Solubilizers Prevent Recrystallization Favoring Accurate and Safe Sun Protection

Sun protection is a global concern, and maximizing sunscreen stability and efficacy depends partially on the prevention of UV filters recrystallization. We aimed to study the efficacy of hydrophobic solubilizers in preventing the recrystallization of solid hydrophobic UV filters in predissolutions, sunscreen formulations, and during simulated human use. Recrystallization of UV filters induced by ultrasonication, temperature variation, or simulated human application was analyzed by different methods. Maximum solubility of UV filters in solubilizers was determined. Surprisingly, the best solubilizer was not necessarily the best solvent to prevent recrystallization, suggesting there are different forces controlling these phenomena. Hydrophobic solubilizers tend to perform better than ethanol in predissolutions, but the presence of other components in final products may change their performance. Results suggest that some UV filters tend to form liquid clusters, which may behave as crystals and affect the desired even distribution of UV filters on the skin. UV filters were also found to respond differently to Hansen Solubility Parameters. Scanning electron microscopy supports the fact that recrystallization upon sunscreen application is an issue to be tested during development. A timesaving method to predict recrystallization of UV filters in clear systems was developed and is presented as a tool to enhance the efficacy of sunscreens.

Should we instruct patients to rub topical agents into skin? The evidence

Background: At least 15 factors influence the ability of compounds to penetrate the skin. Massage (rubbing) may be another factor that has gone relatively unrecognized. Method: PubMed, Google Scholar, and EMBASE databases were accessed online in March 2018 in search of studies measuring absorption through skin with and without rubbing or massage. Results: While some studies noted no difference in dermal absorption with regards to rubbing, others have demonstrated the opposite. In general, massage technique does indeed sometimes enhance dermal absorption. In addition to increase skin temperature and blood flow, rubbing likely modifies stratum corneum (SC) structure to enhance diffusion rates and increase retained penetrant amount within the skin. Conclusions: Understanding the mechanism of massage and its role in percutaneous penetration may help elucidate skin barrier function, dermal absorption, skin decontamination, and dermatotoxicology. To achieve such goals, an in vitro model that models in vivo behaviors must first be established. Subsequently, experiments with different penetrants, vehicles, massage time, and other variables may be considered.

Electrically and Ultrasonically Enhanced Transdermal Delivery of Methotrexate

In this study, we used sonophoresis and iontophoresis to enhance the in vitro delivery of methotrexate through human cadaver skin. Iontophoresis was applied for 60 min at a 0.4 mA/sq·cm current density, while low-frequency sonophoresis was applied at a 20 kHz frequency (2 min application, and 6.9 W/sq·cm intensity). The treated skin was characterized by dye binding, transepidermal water loss, skin electrical resistance, and skin temperature measurement. Both sonophoresis and iontophoresis resulted in a significant reduction in skin electrical resistance as well as a marked increase in transepidermal water loss value (p < 0.05). Furthermore, the ultrasonic waves resulted in a significant increase in skin temperature (p < 0.05). In permeation studies, the use of iontophoresis led to a significantly higher drug permeability than the untreated group (n = 4, p < 0.05). The skin became markedly more permeable to methotrexate after the treatment by sonophoresis than by iontophoresis (p < 0.01). A synergistic effect for the combined application of sonophoresis and iontophoresis was also observed. Drug distribution in the skin layers revealed a significantly higher level of methotrexate in the sonicated skin than that in iontophoresis and untreated groups. Iontophoresis and low-frequency sonophoresis were found to enhance the transdermal and intradermal delivery of methotrexate in vitro.

Poly (vinyl alcohol) microneedles: Fabrication, characterization, and application for transdermal drug delivery of doxorubicin

Poly (vinyl alcohol) microneedles were fabricated, characterized, and applied to enhance in vitro transdermal delivery of doxorubicin. The microneedles were fabricated using the micromolding technique with the drug load in different locations within the needle array. The polymer solution was assessed for rheological properties, drug dissolution, and chemical structurestudies. Microneedles (unloaded) and drug-loaded microneedles were characterized by optical microscopy, fluorescent microscopy, scanning electron microscopy, and drug release kinetics. Successful microporation of dermatomed human cadaver skin was demonstrated by dye binding, pore uniformity, histology, confocal laser microscopy, and skin integrity studies. The microneedles-mediated transdermal delivery of doxorubicin was investigated using vertical Franz diffusion cells. The fabricated microneedles were sharp, strong, and uniform. In vitro permeation studies showed that the microneedle-treated skin (4351.55 ± 560.87 ng/sq.cm) provided a significantly greater drug permeability than the untreated group (0.00 ± 0.00 ng/sq.cm, n = 4, p < 0.01). The drug location within the needle array was found to affect the drug release profile as well as its permeation into and across human skin. Skin microporation achieved by poly (vinyl alcohol) microneedles was found to enhance transdermal delivery of doxorubicin in vitro.

Fabrication, characterization and application of sugar microneedles for transdermal drug delivery

Aim: This study aimed to fabricate, characterize and use maltose microneedles for transdermal delivery of doxorubicin. Materials & methods: Microneedles were fabricated by micromolding technique and evaluated for dimensions, mechanical properties and in situ dissolution. Microporation of human cadaver skin was confirmed by dye binding, histology, pore uniformity, confocal laser microscopy and skin integrity measurement. In vitro permeation studies were performed on vertical Franz diffusion cells. Results: Maltose microneedles were sharp, mechanically uniform and rapidly dissolvable. Microneedle insertion resulted in a marked decrease in lag time and a significant increase in the permeation across and into human skin (p < 0.05). The skin delivery profile was used to predict the steady-state plasma concentration. Conclusion: Maltose microneedles are a promising physical technique to increase skin delivery.