Comparative bioavailability study of an once-a-week matrix versus a twice-a-week reservoir transdermal estradiol delivery systems in postmenopausal women

An open-label, randomised, crossover study was conducted with in healthy postmenopausal women to compare the relative bioavailability of a matrix transdermal estradiol delivery system worn for 7 consecutive days, versus a reservoir transdermal patch worn for 4 days followed by its immediate replacement by another patch worn for further 3 consecutive days. There was a minimum 7-day washout period between the two study periods. Both systems were labelled to release approximately 50 mu g/day of estradiol. Twenty-six subjects were evaluated with regard to estradiol serum levels. Blood samples were taken immediately before and at regular intervals until 192 h after the initiation of each study treatment (patch application) and assayed for estradiol. There was no difference between the patches with regard to C-max. Based on the relative bioavailability, one matrix patch proved to be bioequivalent to two reservoir patches worn consecutively for 7 days. These results demonstrate the ability of one matrix patch to deliver consistent therapeutic levels of estradiol over a 7-day period.