An evaluation of bioequivalence of two 7-day 17beta-estradiol transdermal delivery systems by anatomical site.

An open-label, randomized, crossover study was conducted to assess the bioequivalence of two 7-day transdermal 17beta-estradiol delivery systems following application to the buttock in 42 postmenopausal women. The systems tested were a generic Estradiol Transdermal System (Mylan Pharmaceuticals, Inc.) and Climara (Berlex Laboratories, Inc.), the reference product. Each system was labeled to deliver 17beta-estradiol 0.1 mg/day and was applied for 7 days. Serial serum samples were assayed for estradiol, estrone, and estrone sulfate using validated assays. The bioequivalence confidence intervals for the ratio of log-transformed 17beta-estradiol Cmax values for the Estradiol Transdermal System and Climara were outside the interval of 0.80 to 1.25, indicating that the products were not bioequivalent. Application site reactions and skin irritation were more common with the Estradiol Transdermal System than with Climara. The odds of patch lifting or detachment were 6.95 times higher with the Estradiol Transdermal System than with Climara. Because these two transdermal delivery systems had been previously shown to be bioequivalent after application to the abdomen, the findings of this study suggest that bioequivalence at one anatomical site is not indicative of bioequivalence at another.