Assessment of topical bioavailability in vivo: the importance of stratum corneum thickness.
We present a method to determine the cutaneous bioavailability and hence to evaluate the bioequivalence of topically applied drugs in vivo. The procedure uses serial tape-stripping and transepidermal water loss measurements to quantify the thickness of the removed stratum corneum (SC) and to determine the intact membrane thickness. Following tape-stripping, the drug is extracted from the tapes and assayed, e.g., by HPLC. This provides a drug concentration profile as a function of the normalized position within the SC. The data are fitted to a solution of Fick's second law of diffusion in order to calculate characteristic membrane transport parameters. Integration of the concentration profile over the entire SC thickness, that is, the 'area-under-the-curve', provides a measure of the cutaneous bioavailability and hence can be used to assess the bioequivalence of topically applied drugs.
Kalia
Y N
YN
Centre Interuniversitaire de Recherche et d'Enseignement, Parc d'Affaires International, Archamps, France. kalia@pharma1.cur-archamps.fr
Alberti
I
I
Naik
A
A
Guy
R H
RH
D000287:Administration, Topical; D000818:Animals; D001682:Biological Availability; D006801:Humans; D012867:Skin / Q000033:anatomy & histology*; D012869:Skin Absorption / Q000502:physiology*