Pharmacokinetics of estradiol and of estrone during repeated transdermal or oral administration of estradiol

The estradiol (CAS 50-28-2, E2) and estrone (CAS 53-16-7, E1) concentrations in blood were investigated during a 3-week twice weekly application of an E2 transdermal patch, or daily oral administration of E2 tablets. The transdermal patch (Dermestril 50, hereinafter called "Patch") contains 4 mg E2 and delivers daily 50 micrograms E2. The E2 tablets (hereinafter called "Tablet") contains 2 mg micronized E2. The study was performed on 32 healthy postmenopausal women randomly assigned to two parallel groups, each of 16 subjects, one treated with Patch and the other with Tablet. During the first transdermal Patch application, E2 reached effective concentrations of 30 pg/ml of more 12 h after application. During the following 5 applications the concentrations of E2 remained rather constant (fluctuation = 0.65). The study state was reached with the second Patch, with an average concentration (Cav) of 35 pg/ml. After removal of the last Patch, the E2 concentrations returned to the basal levels within 12 h. The E1 concentrations reached the maximum concentration (Cmax) of 48 pg/ml 41 h after the first Patch application and then remained rather constant (fluctuation = 0.28), with a Cav at steady state of 47 pg/ml. During the oral administration of the first Tablet, E2 reached the peak of 1084 pg/ml 49 min after administration and then decreased rapidly in the following 3 h. There was a progressive cumulation of E2 until steady state, which was reached after the 5th Tablets with a Cav of 418 pg/ml i.e. 12.0 times greater than during Patch, and very large pulses of E2 (fluctuation = 3.68). The E1 concentrations reached the peak of 334 pg/ml 4.28 h after the first administration. The steady was reached with the 14th daily administration. There were Large pulses of E1 (fluctuation = 1.15). The Cav was 441 pg/ml, i.e. 9.4 times greater than during Patch. In conclusion the twice weekly application of the transdermal Patch elicits rather constant and therapeutically effective blood concentrations of E2 and E1. In contrast, the daily oral administration of E2 Tablets elicits large pulses of E2 and E1, and exposes the subjects to high concentrations of E2 and of E1, which are 12.0 and 9.4 times greater, respectively, than those elicited by the Patch. Both treatments were fairly well tolerated, and no withdrawal of the medications during the study was necessary.