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Methodology Issue - Variability

This article discusses significant methodological challenges related to skin stripping techniques used in evaluating drug penetration through the stratum corneum (SC). It highlights issues such as substantial intra- and inter-subject variability, the unreliability of surface strips in assessing drug absorption, and concerns about contamination with unabsorbed drug residues. Furthermore, the article emphasizes the limitations of using stratum corneum concentrations to predict follicular drug concentrations, rendering standardized data normalization for bioavailability studies challenging.

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Methodology Issue - Variability

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  1. Methodology Issue - Variability L.K. Pershing, Cosmetics & Toiletries, 115 (May): 43, 2000

  2. Methodology Issue (L.Latriano, AAPS Workshop, 1996) • Skin stripping is not well controlled. There is largeintra- and inter-subject variability even from adjacent sites.

  3. Methodology Issues • A reliable measure to distinguish between residual surface drug and drug that has been penetrated into SC has yet to be established. • Clinical mass balance studies for most topical products show majority of drug is unabsorbed and can be recovered from skin surface. • Using first 10-20 strips has not been validated as representative of SC. • These strips may be contaminated with unabsorbed drug, calling into question relevance of data. • Even after 40 strips furrows still contain SC tissue and unabsorbed drug ( R.G. van der Molen et al. Arch.Derm.Res. 289:514,1997). • Variability in collection of biosample makes it difficult to normalize the data for evaluation of DPK.

  4. Issues - SC Surrogate For Target Site Time-dependent concentrations in skin strippings and follicles (Schaefer, H. and Redelmeir, T.E. (eds) Skin Barrier, Principles of Percutaneous Absorption, Kruger Publishers, p.198, 1996) • Stratum corneum concentrations do not predict follicular concentrations. DPK cannot be used to assess BA/BE for follicularly delivered drugs.

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