title: Estradiol metabolism during oral and transdermal estradiol replacement therapy in postmenopausal women.
abstract: The metabolism of estradiol was investigated in postmenopausal women after 4 weeks' treatment with oral or transdermal unopposed estradiol. The urinary excretion of the metabolites was examined. With both administration routes, 2-hydroxyestrone, the main A-ring metabolite, and 16alpha-hydroxyestrone, the main D-ring metabolite, were excreted in higher amounts than estradiol and estrone. The ratio of 2-hydroxyestrone to 16alpha-hydroxyestrone remained the same for both administration routes. It has been suggested that dominance of D-ring metabolism, i.e. increase of 16alpha-hydroxyestrone production, is associated with an increased risk of breast cancer. The present study indicates that neither oral nor transdermal estradiol substitution shift this ratio to a higher level of possible risk. Oral estradiol substitution, however, in our study leads to higher metabolite concentrations which may be regarded as hazardous for women with diseases favoring D-ring metabolism.
authors.affiliation: Section of Clinical Pharmacology, University of Tuebigen, Germany.
authors.forename: T H
authors.initials: TH
authors.lastname: Lippert
authors.forename: H
authors.initials: H
authors.lastname: Seeger
authors.forename: A O
authors.initials: AO
authors.lastname: Mueck
mesh_terms: D000279:Administration, Cutaneous; D000284:Administration, Oral; D004958:Estradiol / Q000008:administration & dosage* / Q000493:pharmacokinetics* / Q000652:urine; D004970:Estrone / Q000652:urine; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D006894:Hydroxyestrones / Q000652:urine; D008875:Middle Aged; D017698:Postmenopause; D011863:Radioimmunoassay
chemical_list: D006894:Hydroxyestrones; C026702:16-hydroxyestrone; D004970:Estrone; D004958:Estradiol; C024980:2-hydroxyestrone