In vivo methods for the assessment of topical drug bioavailability

Magnolol and its semi-synthetic derivatives: a comprehensive review of anti-cancer mechanisms, pharmacokinetics, and future therapeutic potential

In recent years, magnolol (MG), a natural active compound of polyphenolic nature, has garnered significant interest for its anti-cancer effects. Numerous studies conducted on cell lines and animal models have indicated a positive impact of administering drugs or semi-synthesized products derived from MG, including a decreased incidence of various cancers. This review aims to illustrate the underlying cellular and molecular basis of its actions. The article includes in-depth explanations of phytochemistry, semi-synthetic derivatives, bioavailability, pharmacokinetics, preclinical research, anti-tumor mechanisms, human clinical studies, toxicity, side effects, and safety. It also demonstrates that, in contrast to the wealth of synthetic medications, MG is highly effective against bladder, colon, gastric, skin, liver, lung, gallbladder, and prostate cancers. The findings of this review indicate that MG is a promising candidate as an anti-tumor agent, and future research should focus on developing new semi-synthetic derivative compounds with potential anti-tumor properties.

Novel Methods Developed in Bioequivalence Assays: Patent Review

This study examines advancements in bioequivalence (BE) assessment methods, with a focus on in vitro-in vivo correlation (IVIVC) and dissolution testing technologies. A systematic patent search was conducted via Espacenet, following PRISMA criteria and the study objectives, revealing 216 relevant patents, of which 28 were selected based on their contributions to novel BE methodologies. Analysis indicates a rapid increase in patent filings from 2021 to 2022, with a significant concentration of contributions from China. Key innovations include enhancements in dissolution testing apparatus, application of physiologically based pharmacokinetic (PBPK) modeling for IVIVC, and advanced statistical approaches for BE assessment. In dissolution testing, ƒ1 and ƒ2 factors remain essential metrics for assessing similarity, especially in solid oral dosage forms. These innovations enhance the efficiency (streamline) of BE evaluations, optimizing the biowaiver process and minimizing the need for extensive clinical trials while ensuring greater precision and reliability. The dissolution test, particularly when combined with PBPK models, allows for predictive evaluation of formulation changes and population-specific responses, fostering efficiency in drug development. Overall, these novel BE assessment approaches provide a framework for regulatory compliance, cost-effective production, and assurance of therapeutic equivalence in generic formulations. While they may not always be implemented in practice, they contribute significantly to innovation in the field, driving advancements in bioequivalence evaluation. This review highlights the evolving landscape of BE and IVIVC methodologies and underscores the importance of incorporating innovative testing approaches to advance pharmaceutical science and regulatory practices.

Developing a method for the study of perfusion effects in topical product pharmacokinetics

Topical drug products are delivered to skin structures to treat numerous skin diseases. Due to the complexities of the skin environment and barrier, topical drug pharmacokinetics are difficult to determine, especially in vivo, as most pharmacokinetic assessment methods can only be performed ex vivo. Notably, in vivo conditions include perfusion via dermal capillaries, which influences topical drug uptake by acting as a clearance route and a "sink" driving permeation through the skin. In this study, we develop a method to examine the effects of perfusion on topical drug uptake in vivo using stimulated Raman scattering (SRS) microscopy, a chemically-specific imaging modality ideal for visualizing topical drug permeation over time. In this pilot study, we imaged the in vivo and ex vivo uptake of tazarotene in 70/30 v/v Transcutol:EtOH in paired mouse ear skin, comparing the effects of perfusion on tazarotene concentration (linearly proportional to SRS signal intensity) over time and pharmacokinetic parameters (Tmax, Cmax, AUC) in lipid-rich and lipid-poor regions in the stratum corneum and sebaceous glands. Obvious variations in SRS signal-time trends and statistically significant differences in stratum corneum pharmacokinetic parameters comparing uptake in lipid-rich and lipid-poor regions in vivo and ex vivo indicated slowed tazarotene flux through ex vivo skin in the absence of perfusion. The observed permeation differences in lipid-rich and lipid-poor regions in perfused and non-perfused skin reflects increased tazarotene permeation rate and removal in the presence of perfusion (in vivo) and decreased permeation rate and lack of elimination route in the absence of perfusion (ex vivo). Our method is demonstrated to be effective in assessing in vivo perfusion effects on topical drug uptake, promoting a better understanding of the influence of perfusion on topical drug delivery.

Evaluation of a Norcantharidin Nanoemulsion Efficacy for Treating B16F1-Induced Melanoma in a Syngeneic Murine Model

Melanoma, a lethal type of cancer originating from melanocytes, is the leading cause of death among skin cancers. While surgical excision of the lesions is the primary treatment for melanoma, not all cases are candidates for surgical procedures. New treatments and complementary options are necessary, given the increasing diagnosis rate. In the present study, a norcantharidin-containing nanoemulsion was developed and evaluated in vivo using a syngeneic graft murine model. Norcantharidin is the demethylated analog of cantharidin, known for its anticancer properties. Our model contemplates surgical excision surgery simulating the standard treatment and the role of the nanoemulsion as a potential adjuvant therapy. We observed a significant decrease in the growth rate of the melanoma lesion in the treated groups compared to the control group, both at the 20th and 30th days of treatment. Moreover, we evaluated the drug bioavailability in serum samples, and the results showed that norcantharidin was detectable in a range of 0.1 to 0.18 mg/mL in the treated groups. Furthermore, histopathological analysis was performed on the amputated tumors, where significant differences were found regarding size, mitosis rate, lymphocytic infiltration, and multispectral quantitative image analysis compared to the control group. If more clinical studies are conducted, the norcantharidin-containing nanoemulsion could be a potential alternative or adjuvant therapy. Topical nanosystems can become or complement standard therapies, which is needed as melanoma affects not only in terms of mortality but also the patient's morbidity and life quality.

Computational Modelling of the Impact of Evaporation on In-Vitro Dermal Absorption

PURPOSE

Volatiles are common in personal care products and dermatological drugs. Determining the impact of evaporation of volatiles on skin permeation is crucial to evaluate and understand their delivery, bioavailability, efficacy and safety. We aim to develop an in-silico model to simulate the impact of evaporation on the dermal absorption of volatiles.

METHOD

The evaporation of volatile permeants was modelled using vapour pressure as the main factor. This model considers evaporation as a passive diffusion process driven by the concentration gradient between the air-vehicle interface and the ambient environment. The evaporation model was then integrated with a previously published physiologically based pharmacokinetic (PBPK) model of skin permeation and compared with published in vitro permeation test data from the Cosmetics Europe ADME Task Force.

RESULTS

The evaporation-PBPK model shows improved predictions when evaporation is considered. In particular, good agreement has been obtained for the distributions in the evaporative loss, and the overall percutaneous absorption. The model is further compared with published in-silico models from the Cosmetics Europe ADME Task Force where favourable results are achieved.

CONCLUSION

The evaporation of volatile permeants under finite dose in vitro permeation test conditions has been successfully predicted using a mechanistic model with the intrinsic volatility parameter vapour pressure. Integrating evaporation in PBPK modelling significantly improved the prediction of dermal delivery.

Oral and topical administration of a geranyl acetophenone attenuates DNCB-induced atopic dermatitis-like skin lesions in BALB/c mice

Atopic dermatitis (AD) is a chronic, allergic inflammatory skin disorder that lacks a definite cure. Using a mouse DNCB-induced AD-like skin lesions model, this study evaluated the potential therapeutic utility of tHGA as an oral and topical treatment for AD. Male BALB/c mice were sensitised and challenged with 1% and 0.5% DNCB on their shaved dorsal skin. Mice in the treatment group were administered tHGA (20, 40, and 80 mg/kg) orally three times per week for 2 weeks, or tHGA (0.2%, 1%, and 5%) topically once daily for 12 days. On day 34, the mice were euthanized, and blood and dorsal skin samples were obtained for analysis. All doses of orally and topically administered tHGA significantly improved scratching, epidermal thickness, blood eosinophilia and mast cell infiltration. There was a minor discrepancy between the two routes of administration, with orally treated tHGA showing significant reductions in Scoring of Atopic Dermatitis (SCORAD), tissue eosinophil infiltration, serum IgE and skin IL-4 levels with treatment of 40 and 80 mg/kg tHGA, whereas topically applied tHGA showed significant reductions in all dosages. These findings suggest that tHGA exhibited therapeutic potential for AD as both oral and topical treatment ameliorates AD-like symptoms in the murine model.

Identification of potent inhibitors of HDAC2 from herbal products for the treatment of colon cancer: Molecular docking, molecular dynamics simulation, MM/GBSA calculations, DFT studies, and pharmacokinetic analysis

The histone deacetylase 2 (HDAC2), an enzyme involved in gene regulation, is a potent drug target for the treatment of colon cancer. Phytocompounds having anticancer properties show the ability to interact with HDAC2 enzyme. Among the compounds, docking scores of caffeic acid (CA) and p-coumaric acid (pCA) with HDAC2 showed good binding efficacy of -5.46 kcal/mol and -5.16 kcal/mol, respectively, with small inhibition constants. The higher binding efficacy of CA compared to pCA can be credited to the presence of an extra oxygen atom in the CA molecule, which forms an additional hydrogen bond with Tyr297. The HDAC2 in complex with these molecules was found to be stable by analyzing RMSD, RMSF, Rg, and SASA values obtained through MD simulations. Furthermore, CA and pCA exhibited low MM/GBSA free energies of -16.32 ± 2.62 kcal/mol and -17.01 ± 2.87 kcal/mol, respectively. The HOMO and LUMO energy gaps, dipole moments, global reactivity descriptor values, and MEP surfaces showed the reactivity of the molecules. The favourable physicochemical and pharmacokinetic properties, along with absence of toxicity of the molecules determined using ADMET analysis, suggested both the acids to be regarded as effective drugs in the treatment of colon cancer.

Lipo-polymeric nano-complexes for dermal delivery of a model protein

Delivering macromolecules across the skin poses challenges due to the barrier properties of stratum corneum. Different strategies have been reported to cross this barrier, such as chemical penetration enhancers and physical methods like microneedles, sonophoresis, electroporation, laser ablation, etc. Herein, we explored a cationic lipo-polymeric nanocarrier to deliver a model protein across the skin. A cationic amphiphilic lipo-polymer was used to prepare blank nanoplexes, which were subsequently complexed with anionic fluorescein-tagged bovine serum albumin (FITC-BSA). Blank nanoplexes and FITC-BSA complexed nanoplexes showed sizes of 93.72 ± 5.8 (PDI-0.250) and 145.9 ± 3.2 nm (PDI-0.258), respectively, and zeta potentials of 25.6 ± 7.0 mV and 9.17 ± 1.20 mV. In vitro cell culture, and toxicity studies showed optimal use of these nanocarriers, with hemocompatibility data indicating non-toxicity. Ex vivo skin permeation analysis showed a skin permeation rate of 33% after 24 h. The optimized formulation was loaded in a carbopol-based gel that exhibits non-Newtonian flow characteristics with shear-thinning behavior and variable thixotropy. The nanoplexes delivered via gel demonstrated skin permeation of 57% after 24 h in mice skin ex vivo. In vivo skin toxicity testing confirmed the low toxicity profile of these nanocarriers. These results are promising for the transdermal/dermal delivery of macromolecules, such as protein therapeutics, using nanoplexes.

Therapeutic, and pharmacological prospects of nutmeg seed: A comprehensive review for novel drug potential insights

Background and objectives

For centuries, plant seed extracts have been widely used and valued for their benefits. They have been used in food, perfumes, aromatherapy, and traditional medicine. These natural products are renowned for their therapeutic properties and are commonly used in medicinal treatments. Their significant pharmacological profiles provide an excellent hallmark for the prevention or treatment of various diseases. In this study, we comprehensively evaluated the biological and pharmacological properties of nutmeg seeds and explored their efficacy in treating various illnesses.

Method

Published articles in databases including Google Scholar, PubMed, Elsevier, Scopus, ScienceDirect, and Wiley, were analyzed using keywords related to nutmeg seed. The searched keywords were chemical compounds, antioxidants, anti-inflammatory, antibacterial, antifungal, antiviral, antidiabetic, anticancer properties, and their protective mechanisms in cardiovascular and Alzheimer's diseases.

Results & discussion

Nutmeg seeds have been reported to have potent antimicrobial properties against a wide range of various bacteria and fungi, thus showing potential for combating microbial infections and promoting overall health. Furthermore, nutmeg extract effectively reduces oxidative stress and inflammation by improving the body's natural antioxidant defense mechanism. Nutmeg affected lipid peroxidation, reduced lipid oxidation, reduced low-density lipoprotein (LDL), and increased phospholipid and cholesterol excretion. In addition, nutmeg extract improves the modulation of cardiac metabolism, accelerates cardiac conductivity and ventricular contractility, and prevents cell apoptosis. This study elucidated the psychotropic, narcotic, antidepressant, and anxiogenic effects of nutmeg seeds and their potential as a pharmaceutical medicine. Notably, despite its sedative and toxic properties, nutmeg ingestion alone did not cause death or life-threatening effects within the dosage range of 20-80 g powder. However, chemical analysis of nutmeg extracts identified over 50 compounds, including flavonoids, alkaloids, and polyphenolic compounds, which exhibit antioxidant properties and can be used as phytomedicines. Moreover, the exceptional pharmacokinetics and bioavailability of nutmeg have been found different for different administration routes, yet, more clinical trials are still needed.

Conclusion

Understanding the chemical composition and pharmacological properties of nutmeg holds promise for novel drug discovery and therapeutic advancements. Nutmeg seed offers therapeutic and novel drug prospects that can revolutionize medicine. By delving into their pharmacological properties, we can uncover the vast potential possibilities of this natural wonder.

Feeding the Body Through the Skin: Ethosomes and Transethosomes as a New Topical Delivery System for Bioactive Compounds

Because the feeding of our body through the oral route can be associated with many drawbacks due to the degradation of natural molecules during transit in the gastrointestinal tract, a transdermal delivery strategy, usually employed in the pharmaceutical field, can present an effective alternative for delivery of bioactives and nutrients from foods. In this review, the chance to feed the body with nutritive and bioactive molecules from food through transdermal administration is discussed. Various nanotechnological devices employed for topical and transdermal delivery of bioactive compounds are described. In addition, mechanisms underlying their potential use in the delivery of nutritive molecules, as well as their capability to efficaciously reach the dermis and promote systemic distribution, are detailed.

A mechanistic insight into the anticancer potentials of resveratrol: Current perspectives

Resveratrol is a widely recognized polyphenolic phytochemical found in various plants and their fruits, such as peanuts, grapes, and berry fruits. It is renowned for its several health advantages. The phytochemical is well known for its anticancer properties, and a substantial amount of clinical evidence has also established its promise as a chemotherapeutic agent. This study focuses on assessing the anticancer properties of resveratrol and gaining insight into the underlying molecular mechanisms. It also evaluates the biopharmaceutical, toxicological characteristics, and clinical utilization of resveratrol to determine its suitability for further development as a reliable anticancer agent. Therefore, the information about preclinical and clinical studies was collected from different electronic databases up-to-date (2018-2023). Findings from this study revealed that resveratrol has potent therapeutic benefits against various cancers involving different molecular mechanisms, such as induction of oxidative stress, cytotoxicity, inhibition of cell migration and invasion, autophagy, arresting of the S phase of the cell cycle, apoptotic, anti-angiogenic, and antiproliferative effects by regulating different molecular pathways including PI3K/AKT, p38/MAPK/ERK, NGFR-AMPK-mTOR, and so on. However, the compound has poor oral bioavailability due to reduced absorption; this limitation is overcome by applying nanotechnology (nanoformulation of resveratrol). Clinical application also showed therapeutic benefits in several types of cancer with no serious adverse effects. We suggest additional extensive studies to further check the efficacy, safety, and long-term hazards. This could involve a larger number of clinical samples to establish the compound as a reliable drug in the treatment of cancer.

Porous microneedle arrays as promising tools for the quantification of drugs in the skin: a proof of concept study

This study aimed to demonstrate the potential of using porous microneedles (PMNs) as a promising tool for the noninvasive quantification of topically applied pharmaceutical products. We fabricated a porous microneedle (PMN) from a blend of cellulose acetate and dimethyl sulfoxide by casting and phase separation; it was characterized using scanning electron microscopy, Raman spectroscopy, differential scanning calorimetry, and a Texture Analyzer. An ex vivo study was conducted as a proof-of-concept study to assess whether this PMN could be used to quantify drug absorption through the skin after the topical administration of two nonequivalent products of sodium ibuprofen (gel and dissolving microneedles). Three cellulose acetate formulations (PMN1: 37.5%, PMN-2: 44.4%, and PMN-3: 50%) were used to prepare PMN patches; subsequently, these were evaluated for their morphological and insertion properties. Only PMN-2 microneedle patches were chosen to continue with the ex vivo study. The ex vivo study results demonstrated that PMNs could absorb and release sodium ibuprofen (SDIB) and differentiate between two different SDIB topical products. This can be attributed to the porous and interconnected architecture of these microneedles. This developmental study highlights the potential success of such a tool for the quantification of dermal drug concentration and supports moving to in vivo tests.

Determining topical product bioequivalence with stimulated Raman scattering microscopy

Generic drugs are essential for affordable medicine and improving accessibility to treatments. Bioequivalence (BE) is typically demonstrated by assessing a generic product's pharmacokinetics (PK) relative to a reference-listed drug (RLD). Accurately estimating cutaneous PK (cPK) at or near the site of action can be challenging for locally acting topical products. Certain cPK approaches are available for assessing local bioavailability (BA) in the skin. Stimulated Raman scattering (SRS) microscopy has unique capabilities enabling continuous, high spatial and temporal resolution and quantitative imaging of drugs within the skin. In this paper, we developed an approach based on SRS and a polymer-based standard reference for the evaluation of topical product BA and BE in human skin ex vivo. BE assessment of tazarotene-containing formulations was achieved using cPK parameters obtained within different skin microstructures. The establishment of BE between the RLD and an approved generic product was successfully demonstrated. Interestingly, within the constraints of the current study design the results suggest similar BA between the tested gel formulation and the reference cream formulation, despite the differences in the formulation/dosage form. Another formulation containing polyethylene glycol as the vehicle was demonstrated to be not bioequivalent to the RLD. Compared to using the SRS approach without a standard reference, the developed approach enabled more consistent and reproducible results, which is crucial in BE assessment. The abundant information from the developed approach can help to systematically identify key areas of study design that will enable a better comparison of topical products and support an assessment of BE.

Update on the advances and challenges in bioequivalence testing methods for complex topical generic products

Most of the government regulatory agencies, including the United States Food and Drug Administration and the European Medicine Agency, demand that the generic complex topical products prove pharmaceutical and bioequivalence. The evaluation of bioequivalence for complex topical dermatological formulations is a challenging task that requires careful consideration of several factors. Although comparative clinical studies are still considered the gold standard approach for establishing bioequivalence in most formulations, these studies can be costly and insensitive to detect formulation differences. Therefore, significant efforts have been made to develop and validate alternative approaches that demonstrate bioequivalence and expedite the availability of high-quality generic topical dermatological products. This article reviews the current methods for determining the bioequivalence of topical formulations in humans, with particular emphasis on recent advances in these methodologies. Most of the alternative methods are sensitive and reproducible, with the capability to ease the financial burden of comparative clinical studies within a short delivery time. The limitations associated with each technique are reviewed in detail.

Assessment of antibiotic release and antibacterial efficacy from pendant glutathione hydrogels using ex vivo porcine skin

Acute bacterial skin and skin structure infections (ABSSSIs) confer a substantial burden on the healthcare system. Local antibiotic delivery systems can provide controlled drug release directly to the site of infection to maximize efficacy and minimize systemic toxicity. The purpose of this study was to examine the antibacterial activity of antibiotic-loaded glutathione-conjugated poly(ethylene glycol) hydrogels (GSH-PEG) against ABSSSIs utilizing an ex vivo porcine dermal explant model. Vancomycin- or meropenem-loaded GSH-PEG hydrogels at 3 different dose levels were loaded over 1 h. Drug release was monitored in vitro under submerged conditions, by the Franz cell diffusion method, and ex vivo utilizing a porcine dermis model. Antibacterial activity was assessed ex vivo on porcine dermis explants inoculated with Staphylococcus aureus or Pseudomonas aeruginosa isolates treated with vancomycin- or meropenem-loaded GSH-PEG hydrogels, respectively. Histological assessment of the explants was conducted to evaluate tissue integrity and viability in the context of the experimental conditions. A dose-dependent release was observed from vancomycin and meropenem hydrogels, with in vitro Franz cell diffusion data closely representing ex vivo vancomycin release, but not high dose meropenem release. High dose vancomycin-loaded hydrogels resulted in a >3 log10 clearance against all S. aureus isolates at 48 h. High dose meropenem-loaded hydrogels achieved 6.5, 4, and 2 log10 reductions in CFU/ml against susceptible, intermediate, and resistant P. aeruginosa isolates, respectively. Our findings demonstrate the potential application of GSH-PEG hydrogels for flexible, local antibiotic delivery against bacterial skin infections.

The Bioavailability of Drugs-The Current State of Knowledge

Drug bioavailability is a crucial aspect of pharmacology, affecting the effectiveness of drug therapy. Understanding how drugs are absorbed, distributed, metabolized, and eliminated in patients' bodies is essential to ensure proper and safe treatment. This publication aims to highlight the relevance of drug bioavailability research and its importance in therapy. In addition to biochemical activity, bioavailability also plays a critical role in achieving the desired therapeutic effects. This may seem obvious, but it is worth noting that a drug can only produce the expected effect if the proper level of concentration can be achieved at the desired point in a patient's body. Given the differences between patients, drug dosages, and administration forms, understanding and controlling bioavailability has become a priority in pharmacology. This publication discusses the basic concepts of bioavailability and the factors affecting it. We also looked at various methods of assessing bioavailability, both in the laboratory and in the clinic. Notably, the introduction of new technologies and tools in this field is vital to achieve advances in drug bioavailability research. This publication also discusses cases of drugs with poorly described bioavailability, providing a deeper understanding of the complex challenges they pose to medical researchers and practitioners. Simultaneously, the article focuses on the perspectives and trends that may shape the future of research regarding bioavailability, which is crucial to the development of modern pharmacology and drug therapy. In this context, the publication offers an essential, meaningful contribution toward understanding and highlighting bioavailability's role in reliable patient treatment. The text also identifies areas that require further research and exploration.

A comprehensive view on the apigenin impact on colorectal cancer: Focusing on cellular and molecular mechanisms

Colon cancer (CC) is one of the most common and deadly cancers worldwide. Oncologists are facing challenges such as development of drug resistance and lack of suitable drug options for CC treatment. Flavonoids are a group of natural compounds found in fruits, vegetables, and other plant-based foods. According to research, they have a potential role in the prevention and treatment of cancer. Apigenin is a flavonoid that is present in many fruits and vegetables. It has been used as a natural antioxidant for a long time and has been considered due to its anticancer effects and low toxicity. The results of this review study show that apigenin has potential anticancer effects on CC cells through various mechanisms. In this comprehensive review, we present the cellular targets and signaling pathways of apigenin indicated to date in in vivo and in vitro CC models. Among the most important modulated pathways, Wnt/β-catenin, PI3K/AKT/mTOR, MAPK/ERK, JNK, STAT3, Bcl-xL and Mcl-1, PKM2, and NF-kB have been described. Furthermore, apigenin suppresses the cell cycle in G2/M phase in CC cells. In CC cells, apigenin-induced apoptosis is increased by inhibiting the formation of autophagy. According to the results of this study, apigenin appears to have the potential to be a promising agent for CC therapy, but more research is required in the field of pharmacology and pharmacokinetics to establish the apigenin effects and its dosage for clinical studies.

Optical Methods for Non-Invasive Determination of Skin Penetration: Current Trends, Advances, Possibilities, Prospects, and Translation into In Vivo Human Studies

Information on the penetration depth, pathways, metabolization, storage of vehicles, active pharmaceutical ingredients (APIs), and functional cosmetic ingredients (FCIs) of topically applied formulations or contaminants (substances) in skin is of great importance for understanding their interaction with skin targets, treatment efficacy, and risk assessment-a challenging task in dermatology, cosmetology, and pharmacy. Non-invasive methods for the qualitative and quantitative visualization of substances in skin in vivo are favored and limited to optical imaging and spectroscopic methods such as fluorescence/reflectance confocal laser scanning microscopy (CLSM); two-photon tomography (2PT) combined with autofluorescence (2PT-AF), fluorescence lifetime imaging (2PT-FLIM), second-harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and reflectance confocal microscopy (2PT-RCM); three-photon tomography (3PT); confocal Raman micro-spectroscopy (CRM); surface-enhanced Raman scattering (SERS) micro-spectroscopy; stimulated Raman scattering (SRS) microscopy; and optical coherence tomography (OCT). This review summarizes the state of the art in the use of the CLSM, 2PT, 3PT, CRM, SERS, SRS, and OCT optical methods to study skin penetration in vivo non-invasively (302 references). The advantages, limitations, possibilities, and prospects of the reviewed optical methods are comprehensively discussed. The ex vivo studies discussed are potentially translatable into in vivo measurements. The requirements for the optical properties of substances to determine their penetration into skin by certain methods are highlighted.

Fundamentals of Skin Bioimpedances

The bioimpedances of tissues beyond the stratum corneum, which is the outermost layer of skin, contain crucial clinical information. Nevertheless, bioimpedance measurements of both the viable skin and the adipose tissue are not widely used, mainly because of the complex multilayered skin structure and the electrically insulating nature of the stratum corneum. Here, a theoretical framework is established for analyzing the impedances of multilayered tissues and, in particular, of skin. Then, strategies are determined for the system-level design of electrodes and electronics, which minimize 4-wire (or tetrapolar) measurement errors even in the presence of a top insulating tissue, thus enabling non-invasive characterizations of tissues beyond the stratum corneum. As an example, non-invasive measurements of bioimpedances of living tissues are demonstrated in the presence of parasitic impedances which are much (e.g., up to 350 times) higher than the bioimpedances of the living tissues beyond the stratum corneum, independently on extreme variations of the barrier (tape stripping) or of the skin-electrode contact impedances (sweat). The results can advance the development of bioimpedance systems for the characterization of viable skin and adipose tissues in several applications, including transdermal drug delivery and the assessment of skin cancer, obesity, dehydration, type 2 diabetes mellitus, cardiovascular risk, and multipotent adult stem cells.

Gel Formulations for Topical Treatment of Skin Cancer: A Review

Skin cancer, with all its variations, is the most common type of cancer worldwide. Chemotherapy by topical application is an attractive strategy because of the ease of application and non-invasiveness. At the same time, the delivery of antineoplastic agents through the skin is difficult because of their challenging physicochemical properties (solubility, ionization, molecular weight, melting point) and the barrier function of the stratum corneum. Various approaches have been applied in order to improve drug penetration, retention, and efficacy. This systematic review aims at identifying the most commonly used techniques for topical drug delivery by means of gel-based topical formulations in skin cancer treatment. The excipients used, the preparation approaches, and the methods characterizing gels are discussed in brief. The safety aspects are also highlighted. The combinatorial formulation of nanocarrier-loaded gels is also reviewed from the perspective of improving drug delivery characteristics. Some limitations and drawbacks in the identified strategies are also outlined and considered within the future scope of topical chemotherapy.

Quantification of Chemical Uptake into the Skin by Vibrational Spectroscopies and Stratum Corneum Sampling

Evaluation of the bioavailability of drugs intended to act within the skin following the application of complex topical products requires the application of multiple experimental tools, which must be quantitative, validated, and, ideally and ultimately, sufficiently minimally invasive to permit use in vivo. The objective here is to show that both infrared (IR) and Raman spectroscopies can assess the uptake of a chemical into the stratum corneum (SC) that correlates directly with its quantification by the adhesive tape-stripping method. Experiments were performed ex vivo using excised porcine skin and measured chemical disposition in the SC as functions of application time and formulation composition. The quantity of chemicals in the SC removed on each tape-strip was determined from the individually measured IR and Raman signal intensities of a specific molecular vibration at a frequency where the skin is spectroscopically silent and by a subsequent conventional extraction and chromatographic analysis. Correlations between the spectroscopic results and the chemical quantification on the tape-strips were good, and the effects of longer application times and the use of different vehicles were clearly delineated by the different measurement techniques. Based on this initial investigation, it is now possible to explore the extent to which the spectroscopic approach (and Raman in particular) may be used to interrogate chemical disposition deeper in the skin and beyond the SC.

Sensitive and effective electrochemical determination of butenafine in the presence of itraconazole using titanium nanoparticles-ionic liquid based nanocomposite sensor

The evaluation of the bioavailability of topically applied medications that act inside or under the skin is a challenging task. Herein, the current study describes a simple, quick, and low-cost electrochemical platform for determining butenafine hydrochloride (BTH) that is mainly prescribed as a treatment of dermatophytosis, applying titanium nanoparticles and an ionic liquid as outstanding mediators. In terms of low detection limits (61.63 nM) and extensive range of 2.21 × 10^-7-13.46 × 10^-5 M, the established electrochemical technique provided worthy analytical performance for butenafine hydrochloride sensing. The suggested sensor's practical applicability was effectively demonstrated in pharmaceutical preparations, actual stratum corneum samples, and simultaneous detection of butenafine hydrochloride and Itraconazole in pharmaceutical preparation for the first time. All of the experimental factors, like the pH and scan rate, have been investigated and optimized. Diffusion coefficients of butenafine hydrochloride at bare and modified sensors were calculated.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11696-022-02593-3.

A novel transdermal ketoprofen formulation for analgesia in cattle

Ketoprofen is registered in many countries for injectable administration in cattle. Because it is soluble in a wide range of excipients, development of a novel transdermal (TD) ketoprofen formulation was pursued to provide a convenient and pain-free route of administration in cattle. One hundred and six excipient combinations were screened using in vitro techniques (Franz diffusion cells), with a 20%_(w/v) ketoprofen formulation dissolved in a combination of 45%:45%_(v/v) ethanol and isopropyl myristate (IPM) and 10%_(v/v) eucalyptus oil achieving maximal penetration of ketoprofen through bovine skin. A bioavailability study was then conducted using a randomized cross-over design (n = 12), including IV, IM (both 3 mg/kg) and TD (10 mg/kg) ketoprofen formulations administered with a one-week washout period between administrations. The IV and IM formulation pharmacokinetic results were as expected. The C_MAX , T_{max and} AUC_0-Last were significantly higher (arithmetic mean ± SD) after TD administration (20.0 ± 6.5 μg/ml, 115 ± 17 min and 3940 ± 1324 μg*min/ml, respectively), compared to IM (11.0 ± 4.0 μg/ml, 74 ± 43 min and 2376 ± 738 μg*min/ml, respectively), although there were no significant differences for T_½β . However, dose corrected values C_MAX and AUC_inf were significantly higher for IM compared to TD. The arithmetic mean bioavailability (F) of the transdermal formulation was 50%. The plasma concentration of the TD formulation at a dose of 10 mg/kg was similar to the IM formulation at 3 mg/kg by 30 min post-dosing with an arithmetic mean ± SD of 7.97 ± 4.38 vs. 8.02 ± 3.55 μg/ml, respectively. The TD formulation was generally well tolerated by cattle, although some local irritation along the site of application was noted after 12 h of exposure during the bioavailability study. Results indicate that this novel TD formulation provides a substantial improvement in administration convenience, may improve animal welfare and end-user safety through needle-free administration, and achieves similar plasma pharmacokinetics to the IM product when administered at 10 mg/kg.

Effect of Salt Form on Gelation and Drug Delivery Properties of Diclofenac-Loaded Poloxamer Gels for Delivery to Impaired Skin

PURPOSE

Treating chronic wounds is a significant clinical challenge, and a topical product would be ideal for pain management. Poloxamer 407, a thermosensitive polymer, would allow an analgesic drug to be topically applied to a wound as a liquid that transitions to a gel at physiologic temperature. Using diclofenac as a model analgesic drug, our goal was to determine effects of salt form on poloxamer gelation and drug delivery from poloxamer gels applied to excised skin with impaired barrier function.

METHODS

Gelation properties of 17% and 20% poloxamer gels loaded with 0.4 to 1.7% diclofenac sodium, potassium, epolamine, or diethylamine were evaluated rheologically. Drug release and delivery were quantified using cellulose membranes, porcine skin, and tape-stripped porcine skin.

RESULTS

Poloxamer gelation temperature increased with higher diclofenac concentration, regardless of salt form; the magnitude of increase varied in the following order: sodium>potassium>diethylamine>epolamine. Gelation temperature differences resulting from the various counterions generally matched previously observed trends of ion-specific effects on macromolecule solubility (the Hofmeister series). Despite changes in gelation behavior, we observed minimal corresponding effects on drug release or delivery. There were no significant differences in diclofenac released or delivered through intact porcine skin over 48 h. However, in studies with impaired (tape-stripped) skin, diclofenac delivery was slowest overall with the epolamine salt.

CONCLUSION

Varying the salt form of a model analgesic drug can impact gelation and drug delivery characteristics of poloxamer systems. Further study of the mechanisms of these changes will be important for continued development of topical poloxamer products for clinical wound care.

The Potential Role of Apigenin in Cancer Prevention and Treatment

Cancer is the leading cause of death worldwide. In spite of advances in the treatment of cancer, currently used treatment modules including chemotherapy, hormone therapy, radiation therapy and targeted therapy causes adverse effects and kills the normal cells. Therefore, the goal of more effective and less side effects-based cancer treatment approaches is still at the primary position of present research. Medicinal plants or their bioactive ingredients act as dynamic sources of drugs due to their having less side effects and also shows the role in reduction of resistance against cancer therapy. Apigenin is an edible plant-derived flavonoid that has received significant scientific consideration for its health-promoting potential through modulation of inflammation, oxidative stress and various other biological activities. Moreover, the anti-cancer potential of apigenin is confirmed through its ability to modulate various cell signalling pathways, including tumor suppressor genes, angiogenesis, apoptosis, cell cycle, inflammation, apoptosis, PI3K/AKT, NF-κB, MAPK/ERK and STAT3 pathways. The current review mainly emphases the potential role of apigenin in different types of cancer through the modulation of various cell signaling pathways. Further studies based on clinical trials are needed to explore the role of apigenin in cancer management and explain the possible potential mechanisms of action in this vista.

Transdermal Drug Delivery: Determining Permeation Parameters Using Tape Stripping and Numerical Modeling

The function of transdermal drug delivery (TDD) systems is complex due to the multiple layers necessary for controlling the rate of drug release and the interaction with the patient’s skin. In this work, we study a particular aspect of a TDD system, that is, the parameters that describe the drug permeation through the skin layers. Studies of the diffusion of two compounds were carried out and supported by tape stripping and numerical modeling. The experimental studies are carried out for porcine skin in a Franz diffusion cell and tape stripping is used to quantify the concentration of drug in the stratum corneum. A multi-layered numerical model, based on Fickian diffusion, is used to determine the unknown parameters that define the skin’s permeability, such as the partition between layers and the mass transfer coefficients due to the surface barrier. A significant correlation was found between the numerical modeling and experimental results, indicating that the partition and mass transfer effects at the interlayer boundary are accurately represented in the numerical model. We find that numerical modeling is essential to fully describe the diffusion characteristics.

Pharmacokinetics of lanoconazole in human skin after repeated topical application

Drug disposition after topical application to the skin has not been fully elucidated, especially after repeated application. We conducted a clinical trial to evaluate the pharmacokinetics in the stratum corneum of healthy adults after repeated application of lanoconazole cream as a model drug. We applied 25 mg of 1% lanoconazole cream onto the pre-specified areas on the participants' back once daily for 5 days. The stratum corneum was sampled twice on each study day using a standardized tape-stripping method, and the amount of lanoconazole contained in the samples was quantified using the tandem mass spectrometry method. The obtained data were used to evaluate lanoconazole pharmacokinetics in the stratum corneum. The amount of lanoconazole in the stratum corneum after once daily repeated administration reached a steady state on day 3, and it was eliminated from the stratum corneum with a half-life of approximately 11 h after discontinuing application.

Cutaneous Pharmacokinetic Approaches to Compare Bioavailability and/or Bioequivalence for Topical Drug Products

The evaluation of bioequivalence (BE) involves comparing the test product to its reference product in a study whose fundamental scientific principles allow inferring of the clinical performance of the products. Several test methods have been discussed and developed to evaluate topical bioavailability (BA) and BE. Pharmacokinetics-based approaches characterize the rate and extent to which an active ingredient becomes available at or near its site of action in the skin. Such methodologies are considered to be among the most accurate, sensitive, and reproducible approaches for determining the BA or BE of a product.

Dermatokinetics: Advances and Experimental Models, Focus on Skin Metabolism

Numerous dermal contact products, such as drugs or cosmetics, are applied on the skin, the first protective barrier to their entrance into the organism. These products contain various xenobiotic molecules that can penetrate the viable epidermis. Many studies have shown that keratinocyte metabolism could affect their behavior by biotransformation. While aiming for detoxification, toxic metabolites can be produced. These metabolites may react with biological macromolecules often leading to sensitization reactions. After passing through the epidermis, xenobiotics can reach the vascularized dermis and therefore be bioavailable and distributed into the entire organism. To highlight these mechanisms, dermatokinetics, based on the concept of pharmacokinetics, has been developed recently. It provides information on the action of xenobiotics that penetrate the organism through the dermal route. The purpose of this review is first to describe and synthesize the dermatokinetics mechanisms to consider when assessing the absorption of a xenobiotic through the skin. We focus on skin absorption and specifically on skin metabolism, the two main processes involved in dermatokinetics. In addition, experimental models and methods to assess dermatokinetics are described and discussed to select the most relevant method when evaluating, in a specific context, dermatokinetics parameters of a xenobiotic. We also discuss the limits of this approach as it is notably used for risk assessment in the industry where scenario studies generally focus only on one xenobiotic and do not consider interactions with the rest of the exposome. The hypothesis of adverse effects due to the combination of chemical substances in contact with individuals and not to a single molecule are being increasingly studied and embraced in the scientific community.

Vegetable Butters and Oils as Therapeutically and Cosmetically Active Ingredients for Dermal Use: A Review of Clinical Studies

While the chemical composition of vegetable butters and oils has been studied in detail, there is limited knowledge about their mechanisms of action after application on the skin. To understand their dermal effects better, 27 clinical studies evaluating 17 vegetable oils (almond, argan, avocado, borage, coconut, evening primrose, kukui, marula, mustard, neem, olive, rapeseed, sacha inchi, safflower, shea butter, soybean and sunflower oils) were reviewed in this research. The reviewed studies focused on non-affected skin, infant skin, psoriasis, xerosis, UVB-induced erythema, atopic dermatitis, molluscum contagiosum, tungiasis, scars, striae and striae gravidarum. We conclude that in inflammation-affected skin, vegetable oils with a high content of oleic acid, together with the lack of or a low linoleic acid content, may cause additional structural damage of the stratum corneum, while oils high in linoleic acid and saturated fatty acids may express positive effects. Non-affected skin, in contrast, may not react negatively to oils high in oleic acid. However, the frequency and duration of an oil's use must be considered an important factor that may accelerate or enhance the negative effects on the skin's structural integrity.

Investigator Impact on Reproducibility of Drug Bioavailability in Stratum Corneum Sampling by Tape Stripping

PURPOSE

Skin sampling by tape stripping measures the local bioavailability of topical drug products in the stratum corneum (SC). The goal of the current study was to evaluate the impact of different investigators in studies that utilize a tape stripping protocol designed to minimize investigator variability.

METHODS

Two open-label clinical studies compared two lidocaine patches and a diclofenac patch and solution in twelve healthy volunteers. The mass of drug was determined in SC samples collected on tape strips at three time points following product removal in duplicate by two investigators. Investigator results were compared with each other and with results for the diclofenac solution measured by another laboratory using a similar protocol.

RESULTS

For drug mass, the geometric mean ratio comparing two investigators is within the acceptable bioequivalence interval for most measurement times and drug products. Drug uptake into the SC from the diclofenac solution was not statistically different from that determined in another laboratory. The average flux from the SC over the clearance intervals for the four drug products correspond well with flux measurements from in vitro permeation tests.

CONCLUSIONS

Results from different investigators are reproducible within the limitations of measurement variability, which can be managed by increasing volunteer numbers.

Assessment of dermal bioavailability: predicting the input function for topical glucocorticoids using stratum corneum sampling

Predicting the dermal bioavailability of topically delivered drugs is challenging. In this work, minimally invasive stratum corneum (SC) sampling was used to quantify the delivery of betamethasone valerate (BMV) into the viable skin. Betnovate® cream (0.1% w/w BMV) was applied at three doses (2, 5, and 10 mg cm-2) to the ventral forearms of 12 healthy volunteers. The mass of drug in the SC was measured using a validated tape-stripping method (a) after a 4-h "uptake" period, and (b) following a 6-h "clearance" period subsequent to cream removal. Concomitantly, the skin blanching responses to the same doses were assessed with a chromameter over 22 h post-application. BMV uptake into the SC was significantly higher for the 5 mg cm-2 dose compared to those of 2 and 10 mg cm-2. In all cases, ~30% of the drug in the SC at the end of the uptake period was cleared in the subsequent 6 h. From the SC sampling data, the average drug flux into the viable epidermis and its first-order elimination rate constant from the SC were estimated as 4 ng cm-2 h-1 and 0.07 h-1, respectively. In contrast, skin blanching results were highly variable and insensitive to the dose of cream applied. The SC sampling method was able to detect a 50% difference between two applied doses with 80% power; detection of a 20% difference would require a larger sample size. SC sampling enabled quantitative metrics describing corticosteroid delivery to the viable epidermis to be determined.

Identification of bioactive molecules from Triphala (Ayurvedic herbal formulation) as potential inhibitors of SARS-CoV-2 main protease (Mpro) through computational investigations

Severe acute respiratory syndrome coronavirus disease (SARS-CoV-2) induced coronavirus disease 2019 (COVID-19) pandemic is the present worldwide health emergency. The global scientific community faces a significant challenge in developing targeted therapies to combat the SARS-CoV-2 infection. Computational approaches have been critical for identifying potential SARS-CoV-2 inhibitors in the face of limited resources and in this time of crisis. Main protease (M^pro) is an intriguing drug target because it processes the polyproteins required for SARS-CoV-2 replication. The application of Ayurvedic knowledge from traditional Indian systems of medicine may be a promising strategy to develop potential inhibitor for different target proteins of SARS-CoV-2. With this endeavor, we docked bioactive molecules from Triphala, an Ayurvedic formulation, against M^pro followed by molecular dynamics (MD) simulation (100 ns) to investigate their inhibitory potential against SARS-CoV-2. The top four best docked molecules (terflavin A, chebulagic acid, chebulinic acid, and corilagin) were selected for MD simulation study and the results obtained were compared to native ligand X77. From docking and MD simulation studies, the selected molecules showed promising binding affinity with the formation of stable complexes at the active binding pocket of M^pro and exhibited negative binding energy during MM-PBSA calculations, indication their strong binding affinity with the target protein. The identified bioactive molecules were further analyzed for drug-likeness by Lipinski's filter, ADMET and toxicity studies. Computational (in silico) investigations identified terflavin A, chebulagic acid, chebulinic acid, and corilagin from Triphala formulation as promising inhibitors of SARS-CoV-2 M^pro, suggesting experimental (in vitro/in vivo) studies to further explore their inhibitory mechanisms.

A personalized FEM model for reproducible measurement of anti-inflammatory drugs in transdermal administration to knee

A personalized model of the human knee for enhancing the inter-individual reproducibility of a measurement method for monitoring Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) after transdermal delivery is proposed. The model is based on the solution of Maxwell Equations in the electric-quasi-stationary limit via Finite Element Analysis. The dimensions of the custom geometry are estimated on the basis of knee circumference at the patella, body mass index, and sex of each individual. An optimization algorithm allows to find out the electrical parameters of each subject by experimental impedance spectroscopy data. Muscular tissues were characterized anisotropically, by extracting Cole-Cole equation parameters from experimental data acquired with twofold excitation, both transversal and parallel to tissue fibers. A sensitivity and optimization analysis aiming at reducing computational burden in model customization achieved a worst-case reconstruction error lower than 5%. The personalized knee model and the optimization algorithm were validated in vivo by an experimental campaign on thirty volunteers, 67% healthy and 33% affected by knee osteoarthritis (Kellgren-Lawrence grade ranging in [1,4]), with an average error of 3%.

Skin pharmacokinetics of diclofenac and co-delivered functional excipients

An important question in the development of a dermatological drug product is whether a target concentration has been achieved in, for example, the viable epidermis following topical administration. When attempting to address this challenge, it is essential to consider the role of excipients in the formulation that may influence drug partitioning and diffusion in the different layers of the skin. The objective, therefore, was to correlate, in human subjects, the skin pharmacokinetics of diclofenac (specifically, its uptake into and clearance from the stratum corneum (SC)) from an approved drug product (Voltaren® medicated plaster) with the in vivo co-uptake of two key excipients, namely propylene glycol and butylene glycol. SC sampling was used to assess diclofenac input into the skin during patch application, and its subsequent clearance post-removal of the delivery system. In parallel the uptake of the two glycol excipients was also measured. Drug and excipient amounts in the SC increased with time of application up to 6 h and, for diclofenac, no further increase was observed when the administration was prolonged to 12 h. When the plaster was removed after 6 h of wear, diclofenac cleared relatively slowly from the SC suggesting that drug binding with a slow off-rate had occurred. The results indicate that the optimisation of drug delivery from a topical formulation must take into account the disposition of key excipients and their impact on dermato-pharmacokinetics in general.

Development challenges for carcinogenicity risk assessments of topical drugs

The nonclinical safety package to support development and approval of drugs intended to be administered by topical application generally follows International Council for Harmonisation multidisciplinary 3 (ICH M3) and topic specific safety (ICH S) guidances. However, some aspects of topical drug development may require case-by-case determination of nonclinical safety strategies. The necessity to conduct a dermal rodent carcinogenicity study is one such example that is not considered an obligate component of a nonclinical safety data package for drug approval. While absence of systemic exposure, as stated in ICH M3, is a primary reason to forego a dermal carcinogenicity assessment, there may also be other factors for consideration in determining the need for a life-time carcinogencity study by dermal route to aid in the overall human cancer risk assessment. We therefore reviewed nonclinical carcinogencity data packages from drugs approved by the FDA or PMDA over a ~25 year time period to evaluate outcomes of oral versus topical carcinogencity studies and to understand their utility for informing the overall human risk assessment. We also discuss various other properties of topical small molecules that could impact the decisions to conduct a dermal life-time rodent carcinogenicity study. Collectively, the need to conduct 2-year dermal carcinogenicity studies in rodents should be determined case-by-case and consider scientific factors such existing systemic toxicity and carcinogenicity study data, anticipated drug exposures in skin, skin evaluation from the chronic minipig toxicity study, and genetic toxicity profile.

CaCO3-based carriers with prolonged release property for antifungal drug delivery to hair follicles

Superficial fungal infections are of serious concern worldwide due to their morbidity and increasing distribution across the globe in this era of growing antimicrobial resistance. Delivery of antifungals to target...

Revisiting techniques to evaluate drug permeation through skin

INTRODUCTION

Investigating the transportation of a drug molecule through various layers of skin and determining the amount of drug retention in skin layers is of prime importance in transdermal and topical drug delivery. The information regarding drug permeation and retention in skin layers aids in optimizing a formulation and provides insight into the therapeutic efficacy of a formulation.

AREAS COVERED

This perspective covers various methods that have been explored to estimate drug/therapeutics in skin layers using in vitro, ex vivo, and in vivo conditions. In vitro methods such as diffusion techniques, ex vivo methods such as isolated perfused skin models and in vivo techniques including dermato-pharmacokinetics employing tape stripping, and microdialysis are discussed. Application of all techniques at various stages of formulation development where various local and systemic effects need to be considered.

EXPERT OPINION

The void in the existing methodologies necessitates improvement in the field of dermatologic research. Standardization of protocols, experimental setups, regulatory guidelines, and further research provides information to select an alternative for human skin to perform skin permeation experiments to increase the reliability of data generated through the available techniques. There is a need to utilize multiple techniques for appropriate dermato-pharmacokinetics evaluation and formulation's efficacy.

Topical drug delivery: History, percutaneous absorption, and product development

Topical products, widely used to manage skin conditions, have evolved from simple potions to sophisticated delivery systems. Their development has been facilitated by advances in percutaneous absorption and product design based on an increasingly mechanistic understanding of drug-product-skin interactions, associated experiments, and a quality-by-design framework. Topical drug delivery involves drug transport from a product on the skin to a local target site and then clearance by diffusion, metabolism, and the dermal circulation to the rest of the body and deeper tissues. Insights have been provided by Quantitative Structure Permeability Relationships (QSPR), molecular dynamics simulations, and dermal Physiologically Based PharmacoKinetics (PBPK). Currently, generic product equivalents of reference-listed products dominate the topical delivery market. There is an increasing regulatory interest in understanding topical product delivery behavior under 'in use' conditions and predicting in vivo response for population variations in skin barrier function and response using in silico and in vitro findings.

Label-free skin penetration analysis using time-resolved, phase-modulated stimulated Raman scattering microscopy

Skin penetration analysis of topically applied drugs or active compounds is essential in biomedical applications. Stimulated Raman scattering (SRS) microscopy is a promising label-free skin penetration analysis tool. However, conventional SRS microcopy suffers from limited signal contrast owing to strong background signals, which prevents its use in low-concentration drug imaging. Here, we present a skin penetration analysis method of topical agents using recently developed phase-modulated SRS (PM-SRS) microscopy. PM-SRS uses phase modulation and time-resolved signal detection to suppress both nonlinear background signals and Raman background signals from a tissue. A proof-of-concept experiment with a topically applied skin moisturizing agent (ectoine) in an in vitro skin tissue model revealed that PM-SRS with 1.7-ps probe delay yields a signal contrast 40 times higher than that of conventional amplitude-modulated SRS (AM-SRS). Skin penetration measurement of a topical therapeutic drug (loxoprofen sodium) showed that the mean drug concentration at the tissue surface layer after 240 min was 47.3 ± 4.8 mM. The proposed PM-SRS microscopy can be employed to monitor the spatial and temporal pharmacokinetics of small molecules in the millimolar concentration regime.

Characterizing Cutaneous Drug Delivery Using Open-Flow Microperfusion and Mass Spectrometry Imaging

Traditionally, cutaneous drug delivery is studied by skin accumulation or skin permeation, while alternative techniques may enable the interactions between the drug and the skin to be studied in more detail. Time-resolved skin profiling for pharmacokinetic monitoring of two Janus Kinase (JAK) inhibitors, tofacitinib and LEO 37319A, was performed using dermal open-flow microperfusion (dOFM) for sampling of perfusate in an ex vivo and in vivo setup in pig skin. Additionally, matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) was performed to investigate depth-resolved skin distributions at defined time points ex vivo in human skin. By dOFM, higher skin concentrations were observed for tofacitinib compared to LEO 37319A, which was supported by the lower molecular weight, higher solubility, lipophilicity, and degree of protein binding. Using MALDI-MSI, the two compounds were observed to show different skin distributions, which was interpreted to be caused by the difference in the ability of the two molecules to interact with the skin compartments. In conclusion, the techniques assessed time- and depth-resolved skin concentrations and were able to show differences in the pharmacokinetic profiles of two JAK inhibitors. Thus, evidence shows that the two techniques can be used as complementary methods to support decision making in drug development.

Physiologically-Based Pharmacokinetic Modeling to Support Determination of Bioequivalence for Dermatological Drug Products: Scientific and Regulatory Considerations

Physiologically-based pharmacokinetic (PBPK) modeling and simulation provides mechanism-based predictions of the pharmacokinetics of an active ingredient following its administration in humans. Dermal PBPK models describe the skin permeation and disposition of the active ingredient following the application of a dermatological product on the skin of virtual healthy and diseased human subjects. These models take into account information on product quality attributes, physicochemical properties of the active ingredient and skin (patho)physiology, and their interplay with each other. Regulatory and product development decision makers can leverage these quantitative tools to identify factors impacting local and systemic exposure. In the realm of generic drug products, the number of US Food and Drug Administratioin (FDA) interactions that use dermal PBPK modeling to support alternative bioequivalence (BE) approaches is increasing. In this report, we share scientific considerations on the development, verification and validation (V&V), and application of PBPK models within the context of a virtual BE assessment for dermatological drug products. We discuss the challenges associated with model V&V for these drug products stemming from the fact that target-site active ingredient concentrations are typically not measurable. Additionally, there are no established relationships between local and systemic PK profiles, when the latter are quantifiable. To that end, we detail a multilevel model V&V approach involving validation for the model of the drug product of interest coupled with the overall assessment of the modeling platform in use while leveraging in vitro and in vivo data related to local and systemic bioavailability.

Topical NSAIDs for acute local pain relief: in vitro characterization of drug delivery profiles into and through human skin

OBJECTIVE

The efficacy of topical nonsteroidal anti-inflammatory drugs (NSAIDs) relates not only to the individual NSAID used but also to differences in formulation design. The aim of this study was to investigate the fundamental differences in ibuprofen and diclofenac drug delivery vehicles, specifically gels and plasters, compared to a recently launched 200 mg ibuprofen medicated plaster and characterize the resulting dermatologic-pharmacokinetic profiles into and through ex vivo human skin layers.

METHODS

In vitro skin permeation testing over 24 h and sacrificial timepoint penetration experiments (at 1, 4, 8, 12, and 24 h) were conducted using an automated flow-through diffusion cell system. The amount of drug delivered to the epidermis, dermis, and receptor solution (representing deeper tissue) was determined by liquid chromatography-tandem mass spectrometry. Skin protein binding of ibuprofen and diclofenac was investigated by spiking skin homogenate with increasing concentrations of each drug and determining the fraction unbound.

RESULTS

Differences were observed in the amount of drug recovered at sacrificial timepoints and rate at which drug was delivered to the target site between plaster and gel formulations of ibuprofen and diclofenac and between plaster formulations of the same drug (ibuprofen). While the amount of drug quantified at sacrificial timepoints did not necessarily determine in vivo flux rates, differences in drug distribution within the skin layers indicated where drug reservoirs were formed.

CONCLUSIONS

These findings highlight the importance of intelligent formulation design in determining NSAID delivery through skin layers. Further work is required to quantify drug delivery into deeper tissues and the resultant local anti-inflammatory effects.

Delivering therapeutic cannabinoids via skin: Current state and future perspectives

Adequate evidence exists in the literature indicating a relatively positive shift with regards to the legal acceptance of cannabis and cannabis-derived products for medicinal purposes in some countries. Concomitantly, scientists are showing renewed interest in cannabis-related research work. Over the years, clinical and preclinical studies have demonstrated the therapeutic significance of cannabinoids for diverse indications. Additionally, efforts are being made to develop cannabis-related products into acceptable prescription products. FDA authorization for the commercial use of four cannabinoid-derived products, available as oral dosage forms is a significant progress already. However, there are certain drawbacks associated with the conventional delivery forms of cannabinoids. These include low oral bioavailability due to hepatic degradation, gastric instability, poor water solubility, and the side effects experienced upon the use of high doses of psychotropic cannabinoids associated with heightened plasma concentrations of the drug. These are however, limitable with the aid of transcutaneous drug delivery. Emerging topical and transdermal strategies could be exploited for the successful development of highly effective delivery systems for cannabinoids. This review discusses the feasibility of delivering therapeutic cannabinoids via skin and provides a comprehensive account of the supporting research studies that have been reported in the literature till date.