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Methodology Issue - Variability

Methodology Issue - Variability. L.K. Pershing, Cosmetics & Toiletries, 115 (May): 43, 2000. Methodology Issue. (L.Latriano, AAPS Workshop, 1996). Skin stripping is not well controlled. There is large intra- and inter-subject variability even from adjacent sites. Methodology Issues.

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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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