The effect of site of application on the transcutaneous absorption of 17-beta estradiol from a transdermal delivery system (Climara)

Objective: The effect of site of application on 17-beta estradiol bioavaila bility was assessed in an open-label, randomized, crossover study of a once -weekly transdermal estradiol patch (Climara). Design: After placement of a transdermal patch delivering 0.1 mg/day of est radiol on either the buttocks or abdomen, serial plasma samples were obtain ed over 7 days and for the immediate 24 h after patch removal. Plasma estra diol concentrations were used to estimate pharmacokinetic parameters for th e rate and extent of absorption between the two sites. Results: Plasma estradiol concentrations were sustained at premenopausal le vels over the week in most subjects. After application on the buttock, mean peak plasma concentration (C-max) was 125.1% and mean relative bioavailabi lity (AUC(0-168)) was 117.2% of that from the abdomen site. Conclusions: in summary, the buttocks seem to be an acceptable site for the application for this once-weekly 17-beta estradiol transdermal delivery sy stem. Because the extent of absorption was significantly more for buttock t han for abdomen application, this application site may provide an advantage in women who experience menopausal symptoms at the end of the week. (Menop ause 2000;7:364-369. (C) 2000, The North American Menopause Society.).