Half-life of estradiol in postmenopausal women.

Estrogen replacement is often advised for postmenopausal women to prevent menopausal symptoms, osteoporosis and heart disease. However, little information is available concerning the half-life of estradiol (E2) in postmenopausal women. This study was designed to determine the half-life and metabolism of transdermal E2. A prospective clinical study of 8 healthy postmenopausal women was performed in the Clinical Research Center of the Brigham and Women's Hospital. A transdermal E2 patch 0.10 mg was placed on the abdominal wall. Thirteen hours later, after an overnight fast, the E2 patch was removed and frequent blood sampling was performed over 6 h. Serum samples were assayed for E2, estrone (E1) and estrone sulfate (E1S). Serum samples were taken before E2 patch placement, for 30 min before patch removal, and for 6 h after patch removal. The basal E2 level of women prior to use of transdermal E2 was 19 +/- 2 pg/ml (mean +/- SE). Thirteen hours after transdermal E2 placement, steady state levels had been reached, with a mean E2 of 112 +/- 6 pg/ml. The mean half-life of E2 after removal of transdermal E2 was 161 min (range 107-221 min). There was a direct relationship between the subjects' weight and the half-life of E2 (r = 0.79, p = 0.02). Mean basal E1 levels were 23 +/- 5 pg/ml and mean E1 steady-state levels after E2 patch placement were 39 +/- 0.6 pg/ml. E1S levels rose from mean basal levels of 1.5 +/- 0.3 ng/ml to mean steady-state levels of 3.1 +/- 0.1 ng/ml after placement of the E2 patch. The apparent half-life of E2 after discontinuing a transdermal E2 patch is 2.7 h or 161 min.