The determination of stratum corneum thickness An alternative approach

Abstract

The individual thickness of the stratum corneum is required to normalize drug permeation profiles in dermatopharmacokinetic studies. The thickness is often estimated using tape-striping combined with transepidermal water loss measurements. A linear transformation of Fick's first law is used to relate the progressively thinner barrier with the corresponding increase in transepidermal water loss and to estimate the thickness by linear regression. However, the data from an important subset of subjects are poorly fitted to this linear model. This is typically due to the removal of loose outer layers of stratum corneum, which do not contribute significantly to barrier function. This work proposes two alternative non-linear models. All three models were used to fit data from 31 in vivo tape-striping experiments and their outcomes and goodness-of-fit compared. The results suggest that the linear model may overestimate the stratum corneum thickness and is open to subjectivity regarding the selection of data points to be fitted. The non-linear models satisfactorily fitted all the data, including all data points. No significant differences were found between the thicknesses derived from the two non-linear models. However, the analysis of the goodness-of-fit of the models to the data suggests a preference for a baseline-corrected approach.

Assessment of Near-Infrared Densitometry for in situ Determination of the Total Stratum Corneum Thickness on Pig Skin: Influence of Storage Time

“…In vivo, the total SC thickness can be analyzed by tape stripping based on measuring the transepidermal water loss (TEWL) [22,23]. However, this method requires an additional accurate measure of the amount of SC on each tape which can be obtained by a number of techniques (weighing, NIR densitometry, protein quantification and optical methods).…”

Improved Bioequivalence Assessment of Topical Dermatological Drug Products Using Dermatopharmacokinetics

“…Ideally, as much of the drug in the SC as possible must be measured as the depth to which a drug penetrates varies in time. There is substantial evidence that the quantity of SC collected by a fixed number of tape strips is highly variable (11)(12)(13) and that often a significant fraction of the SC is not collected (13)(14)(15). Variability in tape adhesives, investigators carrying out the procedures, and site-to-site variation in cohesiveness of the SC within or between subjects all affect the quantity of SC collected on each tape strip.…”

Characterisation of Skin Barrier Function Using Bioengineering and Biophysical Techniques

“…Amino-acid-derived components of NMF in the SC were expressed in terms of amount per unit mass. The change in TEWL as a function of the amount of SC removed was modelled (29) to obtain SC thickness from both the gravimetric and imaging experiments. Extraction fluxes were calculated by dividing the amounts removed during a sampling interval by the duration of that collection period.…”