Abstract
The membrane permeation in vivo of pharmaceuticals is considered to be affected by the proteins present, and this is thought primarily to be due to the bonding of pharmaceuticals with proteins by the Langmuir-type equation. In order to clarify this mechanism, intrinsic permeability constant, Pf, was theoretically derived assuming that the pharmaceuticals bound to proteins do not take part in membrane permeability and that those not bound alone would be taking part. Pf agrees with the apparent permeability constant, P, when the protein concentration is zero. As a model for pharmaceuticals, methyl orange was selected and its permeability through a cellophane membrane in the presence of bovine serum albumin was examined at pH 7.0, with reference to the appropriateness of the theoretical formula. It was thereby found that, while P changed greatly in the presence of bovine serum albumin, Pf remained constant either in the presence or absence of the albumin and agreed with the permeability constant, P°, of methyl orange alone. This fact satisfies the theoretical formula and suggests that only the pharmaceuticals not bond to proteins alone take part in the membrane permeability of pharmaceuticals in the presence of proteins.
