In Vivo Human Transfer of Topical Bioactive Drugs among Individuals: Estradiol*

Studies in percutaneous absorption have shown that a portion of the topical chemical, generally a few percent of the applied dose, became systemically available. This few percent dose absorbed was suffi cient for certain bioactive drugs and led to transdermal drug delivery for systemic application. During the topical drug application period, generally 24 h, mass balance has shown that the majority of the topically applied dose was still on the skin (Wester and Maibach, 1992). In essence, an excess of drug is on the skin through the complete topical dosing period.