Radioisotopic Studies on Percutaneous Absorption. II. Comparison of the Rate of Absorption through Mouse Skin of Several Water-soluble Substances from Emulsion-type Ointments

In a comparison of the percutaneous absorption of 22Na+ with that of 36Cl-, zinc-EDTA-65Zn, ferric-EDTA-59Fe, ferric-tiron-59Fe or ferric-chromotropic acid-59Fe by the"double isotopic method, "it was demonstrated that water-soluble substances added simultaneously to absorption or hydrophilic ointment were absorbed at widely different rates through hair-clipped mouse skin. These results suggest that water-soluble substances added to an emulsion-type ointment may be absorbed through the skin into the body not as emulsified particles themselves but as solution or particles ultimately free of ointment base. It was also demonstrated that percutaneous absorbability of ferric-chromotropic acid-59Fe was significantly lower than that of ferric-tiron-59Fe when a comparison of the rates of absorption of these two radioactive compounds was made indirectly by using the absorption rate of 22Na+ added simutlaneously with each 59Fe-chelate compound to the absorption ointment as a standard. Thus, it was inferred that, when other conditions are similar, the percutaneous absorbability of water-soluble substances from emulsion-type ointment through mouse skin may be decreased with an increase in molecular size.