Estimation of permeability by passive diffusion through Caco-2 cell monolayers using the drugs' lipophilicity and molecular weight.

A recently developed, new theoretical absorption model for passive diffusion through biological membranes describing the dependency of membrane permeability on lipophilicity and molecular size, predicts different sigmoid-hyperbolic permeability-lipophilicity relationships for different molecular weight ranges. This model has been tested with experimental in vitro cultured epithelial cell (Caco-2) permeability data for structurally diverse drugs differing in lipophilicity, ionization state and molecular size. These data were pooled with literature values. Using this simple physicochemical approach, the permeability of a compound through Caco-2 cells by passive diffusion can be predicted from the compounds' distribution coefficient in 1-octanol/water (log D(oct)) and its molecular weight (MW). Deviations from this expected behaviour may point to the involvement of biological components in the transport process, which may require further investigations.