Comparative bioavailability study of two 100-μg daily 17-beta-estradiol transdermal delivery systems:: Once-a-week matrix patch and twice-a-week reservoir patch in healthy postmenopausal women

An open-label, randomized, a-period, crossover study was conducted in healthy postmenopausal women to assess the relative bioavailability of 17-beta-estradiol from a new matrix system versus a standard reservoir transdermal therapeutic system, both labeled to deliver 100 mu g of estradiol per day. The serum estradiol level was assessed immediately before patch application and at various intervals for 192 hours after patch application. Each subject participated in two 8-day treatment periods separated by a minimum 7-day washout period. The subjects were assigned randomly to 1 of the following regimens: (1) 1 matrix patch applied to the abdomen and worn for 7 consecutive days or (2) 1 reservoir patch applied to the abdomen and worn for 4 days, followed immediately by another reservoir patch worn for 3 days. Three hours after the application of both patches, the serum estradiol levels were significantly higher when compared with levels at the time the patch was applied. After 12 hours, the mean serum estradiol level in women who wore the matrix patches was 98.20 +/- 44.97 pg/mL, significantly higher than in women who wore the reservoir patch (62.20 +/- 16.21 pg/mL), The area under the serum estradiol level versus time-curve (AUC) (time, 0-168 hours) with the once-a-week matrix patch was also greater than the AUC with the reservoir patch. These results demonstrate the ability of 1 matrix patch to deliver consistent therapeutic levels of estradiol for a 7-day period. From a pharmacokinetic viewpoint, results of this study suggest that the tested matrix patch tends to be more efficient than the reservoir patch as a transdermal estradiol delivery system.