It has been demanded to develop a formulation for a novel external preparation having excellent transdermal absorption of a basic pharmacologically active component contained therein. It is found that the lipid solubility (logP values) of a basic pharmacologically active component and an organic acid (particularly a fatty acid) contribute significantly to the transdermal absorption of the basic pharmacologically active component in the selection of proper combinations of the basic pharmacologically active component and the organic acid. Namely, it is found that superior transdermal absorption of a basic pharmacologically active component having a lipid solubility level of 0.5 to 5 can be achieved by forming a salt of the component with a fatty acid having a lipid solubility level of -1 to 4. Thus, it becomes possible to provide a novel external preparation having excellent transdermal absorption properties.
