Objective: The effect of site of application on 17-beta estradiol bioavailability 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 estradiol on either the buttocks or abdomen, serial plasma samples were obtained over 7 days and for the immediate 24 h after patch removal. Plasma estradiol concentrations were used to estimate pharmacokinetic parameters for the rate and extent of absorption between the two sites.
Results: Plasma estradiol concentrations were sustained at premenopausal levels over the week in most subjects. After application on the buttock, mean peak plasma concentration (Cmax) was 125.1% and mean relative bioavailability (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 system. Because the extent of absorption was significantly more for buttock than for abdomen application, this application site may provide an advantage in women who experience menopausal symptoms at the end of the week.