Formation of 7 alpha-methyl-ethinyl estradiol during treatment with tibolone.
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.
Wiegratz
Inka
I
Department of Obstetrics and Gynecology, J. W. Goethe University of Frankfurt, Frankfurt, Germany.
Sänger
Nicole
N
Kuhl
Herbert
H
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
D003276:Contraceptives, Oral; D009652:Norpregnenes; D004997:Ethinyl Estradiol; C027385:tibolone