Abstract
The skin permeability of nine steroidal drugs with a different lipophilicity across excised hairless mouse skin was evaluated by the use of an ethanol/panasate 800 (tricaprylin) (40/60) system as a lipophilic vehicle and an ethanol/water (60/40) system as a hydrophilic vehicle. Two different correlations were shown between the skin permeability and n-octanol/water partition coefficient (log P) of the steroidal drugs in the two binary vehicles, respectively : The skin permeability of the drugs was increased with an increase in the hydrophilicity of the drugs by the use of the ethanol/panasate 800 (40/60) binary vehicle, however, the ethanol/water (60/40) binary vehicle showed the contrary tendency in the skin permeability of the drugs. The above results could be explained from the concept of thermodynamic activity of the drug in the vehicle and in the skin by the use of solubility parameter. It was suggested that the solubility parameter of the skin is higher for the ethanol/panasate 800(40/60) vehicle and is lower for the ethanol/water (60/40) vehicle than those of the vehicles, since the skin may be affected by the vehicles. Therefore, it could be considered that the above tendencies are due to an increase of partition of the hydrophilic drug for the ethanol/panasate 800 (40/60) lipophilic binary vehicle and of the lipophilic drug for the ethanol/water (60/40) hydrophilic binary vehicle, to the skin.
