[Bioavailability of 17 beta-estradiol after transdermal administration--dependence on the patch system].

The objective of this study was to compare the pharmacokinetics of serum estradiol concentrations after application of two different transdermal estradiol delivery systems. Ten postmenopausal women (E2 < or = 30 pg/ml; follicle-stimulating hormone > or = 30 mIE/ml) were prospectively randomized to a crossover treatment protocol separated by a 7-day wash out period. The absorption of estradiol was measured after application of a patch either containing 4.0 mg of E2 in a reservoir system or 1.8 mg of E2 in a specially designed matrix system. Although the increase of serum estradiol concentrations after application of the patches with the matrix system was slightly delayed, mean E2 levels over the whole observation period of 80 hours were significantly higher than those achieved with the reservoir system (difference of mean values: 5.1 pg/ml; p < 0.05). This observation was most striking at the end of the observation period and after removal of the patches. Yet, fluctuations of hormone concentrations were greater with the matrix system patches, and the areas under the E2 concentration-time curves were slightly but not significantly increased as compared to these of the patches with the reservoir system (3211 +/- 584 vs. 2556 +/- 249 pg/ml x h). In conclusion, both transdermal estradiol delivery systems are well suited for postmenopausal hormone substitution providing stable serum estradiol concentrations at about 50 pg/ml, with the matrix system possibly increasing the life span of the patch and thus the recommended application period.