Impact of Alkanediols on Stratum Corneum Lipids and Triamcinolone Acetonide Skin Penetration

Skin microincision technique to enhance drug penetration for the treatment of keloid and hypertrophic scars

The synergistic effect of corticosteroids and 5-fluorouracil (5-FU) for the treatment of pathological scarring is widely documented. While topical administration can be a painless, convenient way to convey the two active ingredients, physical enhancement techniques such as microneedling are required to deepen their skin penetration and achieve the therapeutic effect. A novel approach to keloid and scar treatment is given by microincision, i.e., micrometric-sized columnar perforations which allow the drugs to diffuse into the skin and promote tissue proliferation in a more physiological structure. Combining the delivery of triamcinolone acetonide (TAC) and 5-FU with microincision is an innovative approach that could improve the speed and efficacy of regenerative treatments. This study evaluated the effectiveness of the skin treatment with a device combining microincisions and photobiomodulation, in the skin permeation of a combination of TAC and 5-FU. Increasing treatment times (4, 6, and 8 min) led to higher drug penetration compared to intact skin, with a more noticeable effect for 5-FU compared to TAC. Specifically, all treatment durations were significantly more effective (p < 0.05) than the control for 5-FU, while TAC showed less variation between treatments. Moreover, it was shown that in-vitro, the permeation improvement given by the red-light treatment was mainly due to the mechanical massage, which pushed the actives into the microchannels created by the treatment. The application of prolonged skin microincision times ensured much higher skin permeation of both TAC and 5-FU compared to microneedling on healthy excised skin.

Skin penetration enhancers: Mechanistic understanding and their selection for formulation and design

The skin functions as a formidable barrier, particularly the stratum corneum, effectively restricting the penetration of most substances, including therapeutic agents. To circumvent this barrier, skin penetration enhancers (SPEs) are frequently employed to transiently increase skin permeability, facilitating drug absorption without causing irritation or damage. Despite advancements in dermal formulation development, a deeper understanding of the fundamental science underpinning drug delivery via SPEs remains essential. This review delivers a critical update on conventional SPEs, exploring their mechanisms in promoting drug permeation across the skin. In addition to offering an overview of percutaneous drug delivery, we examine the prevailing theories on how SPEs enhance drug transport. Furthermore, we address the intricate interplay between SPEs, drugs and the skin, providing valuable insights into how the molecular properties and permeation behaviours of SPEs influence their efficacy. This comprehensive review aims to support the ongoing development of optimised drug delivery systems for dermal applications by elucidating the complexities and challenges involved in using SPEs effectively.

Current issues in optical monitoring of drug delivery via hair follicles

Drug delivery via hair follicles has attracted much research attention due to its potential to serve for both local and systemic therapeutic purposes. Recent studies on topical application of various particulate formulations have demonstrated a great role of this delivery route for targeting numerous cell populations located in skin and transporting the encapsulated drug molecules to the bloodstream. Despite a great promise of follicle-targeting carriers, their clinical implementation is very rare, mostly because of their poorer characterization compared to conventional topical dosage forms, such as ointments and creams, which have a history spanning over a century. Gathering as complete information as possible on the intrafollicular penetration depth, storage, degradation/metabolization profiles of such carriers and the release kinetics of drugs they contain, as well as their impact on skin health would significantly contribute to understanding the pros and cons of each carrier type and facilitate the selection of the most suitable candidates for clinical trials. Optical imaging and spectroscopic techniques are extensively applied to study dermal penetration of drugs. Current paper provides the state-of-the-art overview of techniques, which are used in optical monitoring of follicular drug delivery, with a special focus on non-invasive in vivo methods. It discusses key features, advantages and limitations of their use, as well as provide expert perspectives on future directions in this field.

Equivalence assessment of creams with quali-quantitative differences in light of the EMA and FDA regulatory framework

EMA and FDA are upgrading guidelines on assessing the quality and the equivalence of topically applied drug products for developing copies of originator products and supporting post-marketing variations. For topical products having remarkably similar composition, both EMA and FDA accept the equivalence on the bases of the comparison of rheological properties and in vitro drug release constant (k) and skin permeation flux (J) values, instead of clinical studies. This work aims to evaluate the feasibility to expand this approach to variations of the composition of complex semi-solid preparations. Ibuprofen (IB) creams at two different strengths (i.e., 1 % and 10 %) were used as a model formulation. Two formulative changes were performed: (a) the addition of the humectant to simulate a minor post-marketing variation; (b) the substitution of the emulsifying system to simulate a major one. These variations impacted only in 1 % IB formulations where both the equivalences of rheological data and J-values failed. At the highest concentration, the presence of IB crystals broke down the differences in rheological patterns and lead the IB thermodynamic activity at the maximum figuring out an overlapping of the J-values. Such data suggest the combination of these studies, which are thought mainly for the development of copies, could be also applied to the management of post-marketing variations that involve product composition.

MALDI-TOF imaging analysis of benzalkonium chloride penetration in ex vivo human skin

Benzalkonium chloride (BZK), alkyldimethylbenzlamonium chloride, is a cationic surfactant that is used as an antiseptic. BZK is classified as a quaternary ammonium compound composed of molecules of several alkyl chains of differing lengths, that dictate its effectiveness towards different microbes. As a result, BZK has become one of the most used preservatives in antibacterial solutions. Despite its widespread use, it is not clear whether BZK penetrates human skin. To answer this question, BZK treated skin was analyzed using matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry imaging. Solutions containing BZK and differing excipients, including citric acid, caprylyl glycol, and vitamin E, were applied ex vivo to excised human skin using Franz diffusion cells. Treated skin was embedded in gelatin and sectioned prior to MALDI-TOF imaging. BZK penetrates through the epidermis and into the dermis, and the penetration depth was significantly altered by pH and additives in tested solutions.

Assessment of penetration and permeation of caffeine by confocal Raman spectroscopy in vivo and ex vivo by tape stripping

OBJECTIVE

Tape stripping is an often-used non-invasive destructive method to investigate the skin penetration of a substance. In recent years, however, the suitability of confocal Raman spectroscopy (CRS) as a non-invasive method of non-destructive examination of the skin has become increasingly apparent. In this study, we compared invasion and depletion penetration and permeation kinetics of a 2% caffeine solution with and without 1,2-pentanediol as a penetration enhancer measured with CRS and tape stripping.

METHODS

Porcine skin was used for tape stripping and human skin for CRS. 2% caffeine solution was applied to the skin for different incubation times. Human skin was then examined by CRS while caffeine was extracted from porcine skin and quantified via reverse-phase HPLC. Fluxes were also measured and calculated by sum of the total amounts of caffeine penetrated into the skin.

RESULTS

Without penetration enhancers, there is hardly any difference between the penetration profiles of the two measurement methods for invasion, but the curves for depletion are different. Furthermore, the calculated flux values for the invasion are almost identical, but for the depletion the tape stripping values are about twice as high as the CRS values.

CONCLUSION

The relevance of conducting invasion and depletion studies became clear and was able to show the still existing problems in the comparability of CRS and tape stripping.

Novel aspects of Raman spectroscopy in skin research

The analytical technology of Raman spectroscopy has an almost 100‐year history. During this period, many modifications and developments happened in the method like discovery of laser, improvements in optical elements and sensitivity of spectrometer and also more advanced light detection systems. Many types of the innovative techniques appeared (e.g. Transmittance Raman spectroscopy, Coherent Raman Scattering microscopy, Surface‐Enhanced Raman scattering and Confocal Raman spectroscopy/microscopy). This review article gives a short description about these different Raman techniques and their possible applications. Then, a short statistical part is coming about the appearance of Raman spectroscopy in the scientific literature from the beginnings to these days. The third part of the paper shows the main application options of the technique (especially confocal Raman spectroscopy) in skin research, including skin composition analysis, drug penetration monitoring and analysis, diagnostic utilizations in dermatology and cosmeto‐scientific applications. At the end, the possible role of artificial intelligence in Raman data analysis and the regulatory aspect of these techniques in dermatology are briefly summarized. For the future of Raman Spectroscopy, increasing clinical relevance and in vivo applications can be predicted with spreading of non‐destructive methods and appearance with the most advanced instruments with rapid analysis time.