Fluorescence-Coupled Techniques for Determining Rose Bengal in Dermatological Formulations and Their Application to Ex Vivo Skin Deposition Studies

Rose Bengal (RB) is a fluorescent dye with several potential biomedical applications, particularly in dermatology. Due to RB's poor physicochemical properties, several advanced delivery systems have been developed as a potential tool to promote its permeation across the skin. Nevertheless, no validated quantitative method to analyse RB within the skin is described in the literature. Considering RB exhibits a conjugated ring system, the current investigation proposes fluorescence-based techniques beneficial for qualitatively and quantitatively determining RB delivered to the skin. Notably, the development and validation of a fluorescence-coupled HPLC method to quantify RB within the skin matrix are herein described for the first time. The method was validated based on the ICH, FDA and EMA guidelines, and the validated parameters included specificity, linearity, LOD, LLOQ, accuracy and precision, and carry-over and dilution integrity. Finally, the method was applied to evaluate RB's ex vivo permeation and deposition profiles when loaded into dermatological formulations. Concerning qualitative determination, multiphoton microscopy was used to track the RB distribution within the skin strata, and fluorescence emission spectra were investigated to evaluate RB's behaviour when interacting with different environments. The analytical method proved specific, precise, accurate and sensitive to analyse RB in the skin. In addition, qualitative side-analytical techniques were revealed to play an essential role in evaluating the performance of RB's dermatological formulation.

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.

Application of an Optimized Tape Stripping Method for the Bioequivalence Assessment of Topical Acyclovir Creams

This study indicates the application of tape stripping (TS) for bioequivalence (BE) assessment of a topical cream product containing 5% acyclovir. A TS method, previously used successfully to assess BE of topical clobetasol propionate and clotrimazole formulations, was used to assess BE of an acyclovir cream (5%) formulation as well as a diluted acyclovir formulation (1.5%) applied to the skin of healthy humans. An appropriate application time was established by conducting a dose duration study using the innovator product, Zovirax® cream. Transepidermal water loss was measured and used to normalize thicknesses between subjects. The area under the curve (AUC) from a plot of amount of acyclovir/strip vs cumulative fraction of stratum corneum (SC) removed was calculated for each application site. BE was assessed using Fieller's theorem in accordance with FDA's guidance for assessment of BE of topical corticosteroids. Adco-acyclovir cream (5%) was found to be BE to Zovirax® cream, where the mean test/reference (T/R) ratio of the AUC's was 0.96 and the bioequivalence interval using a 90% confidence interval was 0.91-1.01 with a statistical power > 95%, whereas the diluted test product fell outside the BE acceptance criteria with T/R ratio of AUC of 0.23 and a 90% CI of 0.20-0.26. This study indicates that the data resulting from the application of this TS procedure has reinforced the potential for its use to assess BE of topical drug products intended for local action, thereby obviating the necessity to undertake clinical trials in patients.

Comprehensive review on additives of topical dosage forms for drug delivery

Skin is the largest organ of the human body and plays the most important role in protecting against pathogen and foreign matter. Three important modes such as topical, regional and transdermal are widely used for delivery of various dosage forms. Among these modes, the topical dosage forms are preferred because it provides local therapeutic activity when applied to the skin or mucous membranes. Additives or pharmaceutical excipients (non-drug component of dosage form) are used as inactive ingredients in dosage form or tools for structuring dosage forms. The main use of topical dosage form additives are controling the extent of absorption, maintaining the viscosity, improving the stability as well as organoleptic property and increasing the bulk of the formulation. The overall goal of this article is to provide the clinician with information related to the topical dosage form additives and their current major applications against various diseases.