GESTODENE AND DESOGESTREL DO NOT HAVE A DIFFERENT INFLUENCE ON CONCENTRATION PROFILES OF ETHINYLESTRADIOL IN WOMEN TAKING ORAL-CONTRACEPTIVES - RESULTS OF ISOTOPE-DILUTION MASS-SPECTROMETRY MEASUREMENTS

Objectives: A new method for the quantitative determination of 17 alph a-ethinylestradiol-17 beta (EE2) in serum is presented here based on t he principle of isotope dilution mass spectrometry (IDMS) with [C-13]E E2 as internal standard, The technique was used to determine the conce ntration profiles of EE2 in the serum of female subjects who had tal;e n oral contraceptives with different progestin components. The method has proved to be very reliable with respect to trueness, specificity p recision and detection sensitivity and offers considerable advantages compared with the immunological methods of measurement used to date. S tudy design: Forty-seven female volunteers took two different oral con traceptives containing EE2 combined with different progestins in accor dance with a cross-over design, After the administration of 30 mu g EE 2 combined with 75 mu g gestodene (EE2/GSD) or 150 mu g desogestrel (E E2/DES), blood samples were taken from the subjects on certain days an d in certain previously specified cycles in the course of 12 h after m edication. Results and conclusions: The biometric analysis of the resu lts showed that the concentration profiles of EE2 were, in their stati stics, significantly equivalent after the administration of either of the two oral contraceptives. The sometimes contradictory results found in former studies after the administration of the different contracep tives were presumably due to the methodological shortcomings of the ra dioimmunological measurement technique. With the use of the highly acc urate and specific technique of IDMS it can now be unequivocally estab lished that the different progestins in the tested oral contraceptives have no influence on the bioavailability of EEL (area under EE2 serum concentration curves, as usually defined in pharmacokinetics).