title: Formation of 7 alpha-methyl-ethinyl estradiol during treatment with tibolone.
abstract: OBJECTIVE
  To investigate whether tibolone, which is orally used for hormone replacement therapy, is transformed to a derivative of ethinyl estradiol (EE).
  
  
  METHODS
  In 10 young women who received 2.5 mg orally administered tibolone daily between cycle day 19 and 25, blood was obtained before and 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 24 h after the last tablet intake. The concentration of 7 alpha-methyl-EE was determined by the gas chromatography with mass spectrometry method.
  
  
  RESULTS
  The results demonstrate that, during daily treatment of women with 2.5 mg tibolone, a small proportion of tibolone is transformed to 7 alpha-methyl-EE. The maximal serum concentrations of 125 +/- 40 pg/mL were in the range of the levels of EE observed during treatment with oral contraceptives containing 30 microg EE.
  
  
  CONCLUSIONS
  Caution is advisable when considering treatment with tibolone of postmenopausal women with contraindications for estrogens.
authors.affiliation: Department of Obstetrics and Gynecology, J. W. Goethe University of Frankfurt, Frankfurt, Germany.
authors.forename: Inka
authors.initials: I
authors.lastname: Wiegratz
authors.forename: Nicole
authors.initials: N
authors.lastname: Sänger
authors.forename: Herbert
authors.initials: H
authors.lastname: Kuhl
mesh_terms: D000328:Adult; D002849:Chromatography, Gas; D003276:Contraceptives, Oral / Q000008:administration & dosage*; D004334:Drug Administration Schedule; D004997:Ethinyl Estradiol / Q000097:blood* / Q000378:metabolism; D005260:Female; D006801:Humans; D009652:Norpregnenes / Q000008:administration & dosage* / Q000378:metabolism*; D011446:Prospective Studies; D018570:Risk Assessment; D012680:Sensitivity and Specificity
chemical_list: D003276:Contraceptives, Oral; D009652:Norpregnenes; D004997:Ethinyl Estradiol; C027385:tibolone