Relationship between the Transference of a Drug from a Transdermal Patch and the Physicochemical Properties

The transferred percentages of 13 drugs to rat skin from transdermal patches were studied to reveal the relationship to their physicochemical properties. The drugs to be tested had melting points of 13.5-234℃, lipophilic indices of 0.475-5.336,and molecular weights of 122.12-392.45. The transferred percentage of drug to intact skin was lower, the higher the melting point, lipophilic index and molecular weight. The same was true in stripped skin, where the transferred percentage of drug was markedly increased. The difference between transferred drug percentages to stripped and intact skin, which could be regarded as the regulatory contribution of the stratum corneum, tended to be larger, the lower the drug's melting point and lipophilic index.