HALF-LIFE OF ESTRADIOL IN POSTMENOPAUSAL WOMEN

Estrogen replacement is often advised for postmenopausal women to prev ent menopausal symptoms, osteoporosis and heart disease. However, litt le information is available concerning the half-life of estradiol (E-2 ) in postmenopausal women. This study was designed to determine the ha lf-life and metabolism of transdermal E-2. A prospective clinical stud y of 8 healthy postmenopausal women was performed in the Clinical Rese arch Center of the Brigham and Women's Hospital. A transdermal E-2 pat ch 0.10 mg was placed on the abdominal wall. Thirteen hours later, aft er an overnight fast, the E-2 patch was removed and frequent blood sam pling was performed over 6 h. Serum samples were assayed for E-2, estr one (E-1) and estrone sulfate (E1S). Serum samples were taken before E -2 patch placement, for 30 min before patch removal, and for 6 h after patch removal. The basal E-2 level of women prior to use of transderm al E-2 was 19 +/- 2 pg/ml (mean +/- SE). Thirteen hours after transder mal E-2 placement, steady state levels had been reached, with a mean E -2 of 112 +/- 6 pg/ml. The mean half-life of E-2 after removal of tran sdermal E-2 was 161 min (range 107-221 min). There was a direct relati onship between the subjects' weight and the half-life of E-2 (r = 0.79 , p = 0.02). Mean basal E-1 levels were 23 +/- 5 pg/ml and mean E-1 st eady-state levels after E-2 patch placement were 39 +/- 0.6 pg/ml. E1S levels rose from mean basal levels of 1.5 +/- 0.3 ng/ml to mean stead y-state levels of 3.1 +/- 0.1 ng/ml after placement of the E-2 patch. The apparent half-life of E-2 after discontinuing a transdermal E-2 pa tch is 2.7 h or 161 min.